Artículos de revistas: "Muscles"

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Azizi, E. "Locomotor function shapes the passive mechanical properties and operating lengths of muscle". Proceedings of the Royal Society B: Biological Sciences 281, n.º 1783 (22 de mayo de 2014): 20132914. http://dx.doi.org/10.1098/rspb.2013.2914.

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Locomotor muscles often perform diverse roles, functioning as motors that produce mechanical energy, struts that produce force and brakes that dissipate mechanical energy. In many vertebrate muscles, these functions are not mutually exclusive and a single muscle often performs a range of mechanically diverse tasks. This functional diversity has obscured the relationship between a muscle's locomotor function and its mechanical properties. I use hopping in toads as a model system for comparing muscles that primarily produce mechanical energy with muscles that primarily dissipate mechanical energy. During hopping, hindlimb muscles undergo active shortening to produce mechanical energy and propel the animal into the air, whereas the forelimb muscles undergo active lengthening to dissipate mechanical energy during landing. Muscles performing distinct mechanical functions operate on different regions of the force–length curve. These findings suggest that a muscle's operating length may be shaped by potential trade-offs between force production and sarcomere stability. In addition, the passive force–length properties of hindlimb and forelimb muscles vary, suggesting that passive stiffness functions to restrict the muscle's operating length in vivo . These results inform our understanding of vertebrate muscle variation by providing a clear link between a muscle's locomotor function and its mechanical properties.

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Locke, M., B. G. Atkinson, R. M. Tanguay y E. G. Noble. "Shifts in type I fiber proportion in rat hindlimb muscle are accompanied by changes in HSP72 content". American Journal of Physiology-Cell Physiology 266, n.º 5 (1 de mayo de 1994): C1240—C1246. http://dx.doi.org/10.1152/ajpcell.1994.266.5.c1240.

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Heat-shock protein 72 (HSP72), the inducible isoform of the HSP70 family, is constitutively expressed in rat hindlimb muscles in proportion to the content of type I muscle fibers. To determine whether this relationship was maintained after fiber transformation, male Sprague-Dawley rats were treated with 3,5,3'-triiodo-DL-thyronine (T3) for 40 days or underwent surgical removal of the left gastrocnemius muscle, after which the left plantaris muscle was allowed to hypertrophy for 30 days. Hypertrophied plantaris muscles exhibited an increased number of type I fibers, type I myosin heavy-chain (MHC) protein, and HSP72 content compared with contralateral muscles. Soleus muscles from rats administered T3 exhibited an increased number of type II fibers, citrate synthase activity, and decreased HSP72 content compared with soleus muscles from controls. These results indicate that the relationship between HSP72 content and type I muscle fiber-MHC composition is maintained when muscles undergo fiber transformation and substantiate that HSP72 content in rat skeletal muscle is not directly linked to a muscle's oxidative capacity.

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ABOALASAAD, ABDELHAMID R. R., BRIGITA K. SIRKOVÁ y GOZDE GONCU-BERK. "Enhancement of muscle’s activity by woven compression bandage". Industria Textila 72, n.º 04 (1 de septiembre de 2021): 408–17. http://dx.doi.org/10.35530/it.072.04.1789.

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Electromyography (EMG) test, the recording of electrical activity in muscle, is a main tool usually used to evaluate themuscle’s activation. This study aims to discuss and analyse the effect of woven compression bandage (WCB) onmuscles’ activation. Flexor Carpi (FC), Soleus (SO), and Medial Gastrocnemius (MG) muscles were selected torepresent the wrist, ankle, and mid-calf muscles respectively, which were then evaluated by EMG electrical voltage testwith and without wearing WCB. The standardized activities used to test the FC muscle were flexion-extension andsqueezing a soft roll. While the protocol activities for MG and SO muscles were flexion-extension and walking actions.Wearing WCB significantly decreased the muscle’s activation and was associated with higher median frequency for bothSO and MG muscles during the tested activities. The EMG signals were analysed and filtered using MegaWin andMATLAB software. Root mean square (RMS) values confirmed that wearing WCB could improve the performance of FC,SO, and MG muscles and might reduce the muscle’s fatigue during the selected activities.

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Haładaj, Robert, Michał Polguj y R. Shane Tubbs. "Comparison of the Superior and Inferior Rectus Muscles in Humans: An Anatomical Study with Notes on Morphology, Anatomical Variations, and Intramuscular Innervation Patterns". BioMed Research International 2020 (30 de abril de 2020): 1–9. http://dx.doi.org/10.1155/2020/9037693.

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A comparison of the superior and inferior rectus muscles was performed to determine whether they have similar structures and innervation attributable to their participation in the same type of, although antagonistic, eye movements. The study was conducted on 70 cadaveric hemiheads, and the anatomical variations in the superior and inferior rectus muscles were assessed. Sihler’s whole mount nerve staining technique was used on 20 isolated superior and 20 isolated inferior rectus muscle specimens to visualize the intramuscular distribution of the oculomotor nerve subbranches. In two cases (~2.8%), variant muscular slips were found that connected the superior and inferior rectus muscles. In 80% of cases, muscular branches arising directly from the inferior branch of the oculomotor nerve innervated the inferior rectus muscle, while in 20% of cases, the nerve to the inferior oblique muscle pierced the inferior rectus muscle and provided its innervation. In 15 of 70 specimens (21.4%), a branch to the levator palpebrae superioris muscle pierced the superior rectus muscle. The distance between the specific rectus muscle’s insertion and the anterior-most terminations of the nerves’ subbranches with reference to the muscle’s total length ranged from 26.9% to 47.2% for the inferior rectus and from 34.8% to 46.6% for the superior rectus, respectively. The superior rectus muscle is slightly longer and its insertion is farther from the limbus of the cornea than is the inferior rectus muscle. Both muscles share a common general pattern of intramuscular nerve subbranches’ arborization, with characteristic Y-shaped ramifications that form the terminal nerve plexus located near half of the muscles’ length. Unexpected anatomical variations of the extraocular muscles may be relevant during orbital imaging or surgical procedures.

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Lieber, Richard L. y Samuel R. Ward. "Skeletal muscle design to meet functional demands". Philosophical Transactions of the Royal Society B: Biological Sciences 366, n.º 1570 (27 de mayo de 2011): 1466–76. http://dx.doi.org/10.1098/rstb.2010.0316.

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Skeletal muscles are length- and velocity-sensitive force producers, constructed of a vast array of sarcomeres. Muscles come in a variety of sizes and shapes to accomplish a wide variety of tasks. How does muscle design match task performance? In this review, we outline muscle's basic properties and strategies that are used to produce movement. Several examples are provided, primarily for human muscles, in which skeletal muscle architecture and moment arms are tailored to a particular performance requirement. In addition, the concept that muscles may have a preferred sarcomere length operating range is also introduced. Taken together, the case is made that muscles can be fine-tuned to perform specific tasks that require actuators with a wide range of properties.

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Shahin, Karima A. y R. T. Berg. "Growth and distribution of individual muscles in Double Muscled and normal cattle". Journal of Agricultural Science 105, n.º 3 (diciembre de 1985): 479–90. http://dx.doi.org/10.1017/s0021859600059347.

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SUMMARYEighteen Double Muscled (DM), 18 Beef Synthetic and 18 Hereford bulls, serially slaughtered from approximately 250 to 800 kg live weight, were used to examine the influence of maturity type and Double Muscling on individual muscle growth patterns and distribution.Breed types differed significantly in the relative growth rate of five of the 95 muscles. Individual muscles grew and developed at relatively different rates with muscles associated with locomotion being early developing followed by those associated with structure or posture and finally those which respond to sexual maturation or luxury muscles which were late developing. Individual muscle growth patterns revealed an increasing disto-proximal gradient along the limbs and an increasing caudo-cranial gradient along the whole body. However, within any anatomical region considerable variations with well defined growth gradients were found for individual muscles. In the proximal region of both limbs increasing medio-lateral growth gradients were apparent.At the same total side muscle, breed types differed significantly in adjusted mean weights of 33 of the 95 muscles. When comparison was made at the same total side muscle, DM showed a range of hypertrophy of + 28% to -28% when compared with the more normal breed types.Muscular hypertrophy followed a disto-proximal gradient along the limbs and an inner–outer gradient across the muscle layers with the superficial and bulkiest muscles being the most hypertrophied. At the same total side muscle, DM had heavier expensive or luxury muscles than normal cattle.

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Bergmeister, Konstantin D., Martin Aman, Silvia Muceli, Ivan Vujaklija, Krisztina Manzano-Szalai, Ewald Unger, Ruth A. Byrne et al. "Peripheral nerve transfers change target muscle structure and function". Science Advances 5, n.º 1 (enero de 2019): eaau2956. http://dx.doi.org/10.1126/sciadv.aau2956.

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Selective nerve transfers surgically rewire motor neurons and are used in extremity reconstruction to restore muscle function or to facilitate intuitive prosthetic control. We investigated the neurophysiological effects of rewiring motor axons originating from spinal motor neuron pools into target muscles with lower innervation ratio in a rat model. Following reinnervation, the target muscle’s force regenerated almost completely, with the motor unit population increasing to 116% in functional and 172% in histological assessments with subsequently smaller muscle units. Muscle fiber type populations transformed into the donor nerve’s original muscles. We thus demonstrate that axons of alternative spinal origin can hyper-reinnervate target muscles without loss of muscle force regeneration, but with a donor-specific shift in muscle fiber type. These results explain the excellent clinical outcomes following nerve transfers in neuromuscular reconstruction. They indicate that reinnervated muscles can provide an accurate bioscreen to display neural information of lost body parts for high-fidelity prosthetic control.

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Afnan, Zavata, Arshad Nawaz Malik, Saira Jahan y Arshad Ali. "Association of muscles length and strength with balance and functional status among children with diplegic spastic cerebral palsy". Journal of the Pakistan Medical Association 73, n.º 2 (15 de enero de 2023): 253–57. http://dx.doi.org/10.47391/jpma.5174.

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Objective: To determine the correlation of muscle length and muscle strength with balance and functional status among children with diplegic spastic cerebral palsy. Method: The cross-sectional study was conducted from February to July 2021 at the Physical Therapy Department of Chal Foundation and Fatima Physiotherapy Centre, Swabi, Pakistan, and comprised children aged 4-12 years with diplegic spastic cerebral palsy. The strength of back and lower limb muscles was assessed through manual muscles testing. Lower limb muscle’s length, indicating tightness, was assessed using goniometer. Paediatric balance scale and gross motor function measure scale-88 were used to assess balance and gross motor function. Data was analysed using SPSS 23. Results: Of the 83 subjects, 47(56.6%) were boys and 36(43.4%) were girls. The overall mean age was 7.31±2.02 years, mean weight was 19.71±5.45kg, mean height was 105.5±14cm and mean body mass index was 17.32±1.64 kg/m2. There was a positive and significant correlation of all the lower limb muscles’ strength with balance (p<0.01) and functional status (p<0.01). The correlation between the tightness of muscles and balance was significant and negative for all lower limb muscles (p<0.005). The correlation between the muscles’ tightness and functional status was negative and significant for all lower limb muscles (p<0.005). Conclusion: Good muscle strength and appropriate flexibility of lower limb muscles enhanced functional status and good balance in children with diplegic spastic cerebral palsy. Key Words: Balance, Cerebral palsy, Diplegic cerebral palsy, Functional status, Muscle length, Muscle strength.

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Acevedo, Luz M., Ana I. Raya, Rafael Ríos, Escolástico Aguilera-Tejero y José-Luis L. Rivero. "Obesity-induced discrepancy between contractile and metabolic phenotypes in slow- and fast-twitch skeletal muscles of female obese Zucker rats". Journal of Applied Physiology 123, n.º 1 (1 de julio de 2017): 249–59. http://dx.doi.org/10.1152/japplphysiol.00282.2017.

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A clear picture of skeletal muscle adaptations to obesity and related comorbidities remains elusive. This study describes fiber-type characteristics (size, proportions, and oxidative enzyme activity) in two typical hindlimb muscles with opposite structure and function in an animal model of genetic obesity. Lesser fiber diameter, fiber-type composition, and histochemical succinic dehydrogenase activity (an oxidative marker) of muscle fiber types were assessed in slow (soleus)- and fast (tibialis cranialis)-twitch muscles of obese Zucker rats and compared with age (16 wk)- and sex (females)-matched lean Zucker rats ( n = 16/group). Muscle mass and lesser fiber diameter were lower in both muscle types of obese compared with lean animals even though body weights were increased in the obese cohort. A faster fiber-type phenotype also occurred in slow- and fast-twitch muscles of obese rats compared with lean rats. These adaptations were accompanied by a significant increment in histochemical succinic dehydrogenase activity of slow-twitch fibers in the soleus muscle and fast-twitch fiber types in the tibialis cranialis muscle. Obesity significantly increased plasma levels of proinflammatory cytokines but did not significantly affect protein levels of peroxisome proliferator-activated receptors PPARγ or PGC1α in either muscle. These data demonstrate that, in female Zucker rats, obesity induces a reduction of muscle mass in which skeletal muscles show a diminished fiber size and a faster and more oxidative phenotype. It was noteworthy that this discrepancy in muscle's contractile and metabolic features was of comparable nature and extent in muscles with different fiber-type composition and antagonist functions. NEW & NOTEWORTHY This study demonstrates a discrepancy between morphological (reduced muscle mass), contractile (shift toward a faster phenotype), and metabolic (increased mitochondrial oxidative enzyme activity) characteristics in skeletal muscles of female Zucker fatty rats. It is noteworthy that this inconsistency was comparable (in nature and extent) in muscles with different structure and function.

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SHAHIN, KARIMA A. y R. T. BERG. "GROWTH AND DISTRIBUTION OF MUSCLE IN DOUBLE MUSCLED AND NORMAL CATTLE". Canadian Journal of Animal Science 65, n.º 2 (1 de junio de 1985): 307–18. http://dx.doi.org/10.4141/cjas85-037.

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Eighteen Double Muscled (DM), 18 Beef Synthetic (SY) and 18 Hereford (HE) bulls, serially slaughtered from approximately 250 to 800 kg liveweight, were used to determine the influence of maturity type and "double muscling" upon muscle growth patterns and distribution. The left side of each carcass was dissected into major carcass tissues and the weights of individual muscles were obtained and grouped into nine standard anatomical groups. Relative to total side msucle (TSM), breed types tended to have similar growth coefficients for all muscle groups except muscles surrounding the spinal column where HE tended to have a higher growth coefficient than either DM or SY. As TSM increased, the proportion of muscle found in proximal hindlimb, distal hindlimb and distal forelimb decreased (b < 1; P < 0.05), the proportion of muscle in abdominal wall and proximal forelimb remained relatively constant (b = 1; P > 0.05) and the proportion of muscle in thorax to forelimb, neck to forelimb and intrinsic muscles of neck and thorax increased (b > 1; P < 0.05). At the same TSM, compared with the other breed types, DM tended to have more of their muscle in the hip and stifle region but less in the distal parts of both limbs and in neck and thorax. The hyperdevelopment of the large superficial muscles of the proximal part (thigh) and the hypodevelopment of the distal part in the hindlimb give the DM animal the typical 'bottle thigh' appearance. Key words: Bulls (young), muscle growth, muscle distribution, Double Muscled, cattle

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Azizi, Emanuel y Emily M. Abbott. "Anticipatory motor patterns limit muscle stretch during landing in toads". Biology Letters 9, n.º 1 (23 de febrero de 2013): 20121045. http://dx.doi.org/10.1098/rsbl.2012.1045.

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To safely land after a jump or hop, muscles must be actively stretched to dissipate mechanical energy. Muscles that dissipate energy can be damaged if stretched to long lengths. The likelihood of damage may be mitigated by the nervous system, if anticipatory activation of muscles prior to impact alters the muscle's operating length. Anticipatory motor recruitment is well established in landing studies and motor patterns have been shown to be modulated based on the perceived magnitude of the impact. In this study, we examine whether motor recruitment in anticipation of landing can serve a protective function by limiting maximum muscle length during a landing event. We use the anconeus muscle of toads, a landing muscle whose recruitment is modulated in anticipation of landing. We combine in vivo measurements of muscle length during landing with in vitro characterization of the force–length curve to determine the muscle's operating length. We show that muscle shortening prior to impact increases with increasing hop distance. This initial increase in muscle shortening functions to accommodate the larger stretches required when landing after long hops. These predictive motor strategies may function to reduce stretch-induced muscle damage by constraining maximum muscle length, despite variation in the magnitude of impact.

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Evans, C. G., S. Rosen, I. Kupfermann, K. R. Weiss y E. C. Cropper. "Characterization of a radula opener neuromuscular system in Aplysia". Journal of Neurophysiology 76, n.º 2 (1 de agosto de 1996): 1267–81. http://dx.doi.org/10.1152/jn.1996.76.2.1267.

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1. Several lines of evidence suggest that the I7-I10 muscle group contributes to the radula opening phase of behavior in Aplysia; 1) extracellular stimulation of these muscles in reduced preparations causes the halves of the radula to separate, 2) synaptic activity can be recorded from muscles I7-I10 in intact animals when the radula is opening, and 3) motor neurons innervating I7-I10 are activated out of phase with retractor/closer motor neurons during cycles of buccal activity driven by the cerebral-to-buccal interneuron 2 (CBI-2). 2. All of the opener muscles are innervated by the B48 neurons, a bilaterally symmetrical pair of cholinergic motor neurons. B48 neurons produce excitatory junction potentials (EJPs) in opener muscle fibers that summate to produce muscle contractions. Contraction size is determined by the size of depolarization in muscle fibers and/or by action potentials that are triggered by summation of B48-evoked EJPs. 3. In addition to input from B48 neurons, opener muscles also receive excitatory input from the cholinergic multiaction neurons B4/B5. EJPs evoked by stimulation of neurons B4/B5 are 1/10 the size of B48-evoked EJPs. Consequently, changes in muscle tension produced by B4/B5 activity are relatively small. In contrast to B48 neurons, neurons B4/B5 are likely to be active during the closing/retraction phase of behavior. During cycles of buccal activity driven by neuron CBI-2, neurons B4/B5 fire in phase with closer/retractor motor neurons. Thus opener muscles may develop a modest amount of tension during the closing/retraction phase of behavior as a result of synaptic input from neurons B4/B5. 4. Opener muscles may also develop tension during closing/retraction simply by virtue of the fact that they have been stretched. When isolated opener muscles are lengthened, depolarizations are recorded from individual muscle fibers, and muscle tension increases. With sufficient changes in fiber length, action potentials are elicited. These action potentials produce twitchlike muscle contractions that become rhythmic with maintained stretch. Stretch-activated depolarizations are generally first apparent when muscle length is increased by 1 mm. Length changes of 4-5 mm are generally necessary to elicit twitchlike muscle contractions. Changes of 1-2 mm in muscle length are observed when the opener muscle's antagonist, the accessory radula closer, is activated in reduced preparations. 5. Stretch may also modulate B48-induced contractions of the opener muscles. When muscle length is increased, B48-elicited contractions of the I7 muscle are larger. These increases in contraction amplitude are accompanied by decreases in contraction latency. 6. We conclude that muscles I7-I10 contract vigorously in response to strong excitatory input from neuron B48 and contribute to radula opening. Stretch may potentiate this activity. Thus, if radula closer muscles contract vigorously and pull on the opener muscles, the opener muscles will respond by contracting more vigorously themselves. This may be a mechanism for maintaining amplitude relationships between antagonistic muscles. Additionally, it is likely that the opener muscles will develop at least a modest amount of tension during closure/retraction of the radula. Part of this activation may derive from the weak excitatory input that the muscles receive from neurons B4/B5. Another part may derive from the stretch. One function of this co-contraction may be to act as a brake on closure, bringing this phase of feeding behavior to a smooth halt.

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Ullauri, Jessica Beltran, Yasuhiro Akiyama, Shogo Okamoto y Yoji Yamada. "Biomechanical Analysis of Gait Compensation Strategies as a Result of Muscle Restriction". Applied Sciences 11, n.º 18 (8 de septiembre de 2021): 8344. http://dx.doi.org/10.3390/app11188344.

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The loss of muscle mass with aging and consequent muscle weakness results in compensatory gait motions. Although these compensatory motions increase the cost of walking, they appear to be an attempt by the elderly to maintain safe ambulation. However, the relationship between the affected muscles and compensatory motions in the gait cycle is unclear. This study examined gait compensation in young subjects whose muscles were weakened with Muscle Activity Restriction Taping Technique, which restricts the muscle’s belly by tightening the lower limb(s). The study included different walking speeds (regular/slow) and restrictions (calf muscles/both calf and thigh muscles). It revealed that there was an active kinematic compensation chain, in which the non-restricted or less-restricted joints compensated for the affected joint to prevent foot drop, knee hyperextension in the terminal stance phase, and knee hyperflexion in the loading response phase, and to maintain the step length. Furthermore, joints could compensate for themselves when the muscles acting on the other joints were unable to assist, as observed on an ankle joint that compensated for itself to prevent foot drop when the knee and hip flexor muscles were restricted. Moreover, the observed compensation strategies agreed with a previously reported simulation on the gait compensations appearing along with muscle weakness. This study includes a comparison of these compensation strategies with those reported for the elderly. The results of this study provide an understanding of the mechanisms of gait compensation against limitations of gait ability.

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del-Ama, Antonio, Aikaterini Koutsou, Elisabeth Bravo-Esteban, Julio Gómez-Soriano, Stefano Piazza, Ángel Gil-Agudo, José Pons y Juan Moreno. "A comparison of customized strategies to manage muscle fatigue in isometric artificially elicited muscle contractions for incomplete SCI subjects". Journal of Automatic Control 21, n.º 1 (2013): 19–25. http://dx.doi.org/10.2298/jac1301019a.

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Muscle fatigue due to functional electrical stimulation still prevents its widespread use as a gait rehabilitation tool for spinal cord injured subjects. Although there is an active research towards optimization of pulse parameters to delay muscle fatigue, changes in stimulated muscle's performance during repeated contractions due to fatigue have not been yet determined. In this work, a study conducted in two phases with a sample of incomplete spinal cord injured patients is presented. In the first phase, a fatigue protocol based on submaximal isometric contractions allowed to obtain an objective criterion for estimation of fatigue of knee muscles from initial changes in muscle performance. The criterion is incorporated in the fatigue protocol in the second phase of the study, to compare two novel customized fatigue management strategies. Results showed that knee flexor muscles develop less force and lower fatigue than extensor muscles. Muscle fatigue management strategies based on customized modulations of stimulation frequency are valid to delay muscle fatigue.

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Houle-Leroy, Philippe, Helga Guderley, John G. Swallow y Theodore Garland. "Artificial selection for high activity favors mighty mini-muscles in house mice". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 284, n.º 2 (1 de febrero de 2003): R433—R443. http://dx.doi.org/10.1152/ajpregu.00179.2002.

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After 14 generations of selection for voluntary wheel running, mice from the four replicate selected lines ran, on average, twice as many revolutions per day as those from the four unselected control lines. To examine whether the selected lines followed distinct strategies in the correlated responses of the size and metabolic capacities of the hindlimb muscles, we examined mice from selected lines, housed for 8 wk in cages with access to running wheels that were either free to rotate (“wheel access” group) or locked (“sedentary”). Thirteen of twenty individuals in one selected line (line 6) and two of twenty in another (line 3) showed a marked reduction (∼50%) in total hindlimb muscle mass, consistent with the previously described expression of a small-muscle phenotype. Individuals with these “mini-muscles” were not significantly smaller in total body mass compared with line-mates with normal-sized muscles. Access to free wheels did not affect the relative mass of the mini-muscles, but did result in typical mammalian training effects for mitochondrial enzyme activities. Individuals with mini-muscles showed a higher mass-specific muscle aerobic capacity as revealed by the maximal in vitro rates of citrate synthase and cytochrome c oxidase. Moreover, these mice showed the highest activities of hexokinase and carnitine palmitoyl transferase. Females with mini-muscles showed the highest levels of phosphofructokinase, and males with mini-muscles the highest levels of pyruvate dehydrogenase. As shown by total muscle enzyme contents, the increase in mass-specific aerobic capacity almost completely compensated for the reduction caused by the “loss” of muscle mass. Moreover, the mini-muscle mice exhibited the lowest contents of lactate dehydrogenase and glycogen phosphorylase. Interestingly, metabolic capacities of mini-muscled mice resemble those of muscles after endurance training. Overall, our results demonstrate that during selection for voluntary wheel running, distinct adaptive paths that differentially exploit the genetic variation in morphological and physiological traits have been followed.

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Lapier, T. K., H. W. Burton, R. Almon y F. Cerny. "Alterations in intramuscular connective tissue after limb casting affect contraction-induced muscle injury". Journal of Applied Physiology 78, n.º 3 (1 de marzo de 1995): 1065–69. http://dx.doi.org/10.1152/jappl.1995.78.3.1065.

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This study examined the effect of alterations in rat intramuscular connective tissue (CT), secondary to limb immobilization, on the muscle's susceptibility to contraction-induced injury. Hindlimbs were casted for 3 wk with the extensor digitorum longus muscle fixed in a shortened (IM-SP) or lengthened position (IM-LP). An age-matched control group remained uncasted. Extensor digitorum longus muscles were injured in vivo by using a motorized foot pedal that repeatedly flexed and extended the foot while the muscle was electrically stimulated during plantar flexion. Four hours postinjury, maximum isometric tetanic force (Po) was measured in vitro and was used as a functional index of muscle injury. Muscles were fixed, sectioned, and stained for later analysis. Intramuscular CT concentration, expressed as the ratio of CT area to muscle fiber area, was significantly higher in both IM-SP (0.153 +/- 0.003) and IM-LP (0.174 +/- 0.003) groups compared with controls (0.104 +/- 0.003). Po values of injured muscles both IM-LP and IM-SP were higher than the injured controls' Po of 9.41 +/- 0.63 N/cm2 (P < 0.05). Injured IM-LP muscle forces were significantly higher than those of IM-SP. This study demonstrated that limb immobilization increases intramuscular CT concentration, which is accompanied by attenuation of muscle injury. We conclude that remodeling of intramuscular CT affects the muscle's resistance to contraction-induced injury.

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Bickel, C. Scott, Jill M. Slade, Gordon L. Warren y Gary A. Dudley. "Fatigability and Variable-Frequency Train Stimulation of Human Skeletal Muscles". Physical Therapy 83, n.º 4 (1 de abril de 2003): 366–73. http://dx.doi.org/10.1093/ptj/83.4.366.

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Abstract Background and Purpose. The quadriceps femoris (QF) and tibialis anterior (TA) muscles are often activated through the use of electrical stimulation by physical therapists. These 2 muscles are fundamentally different in regard to their fiber-type composition. Whether protocols developed using a given muscle can be applied to another muscle has seldom been questioned, even if they differ in fiber type. The purpose of this study was to test the hypothesis that torque augmentation during variable-frequency train (VFT) stimulation as compared with constant-frequency train (CFT) stimulation in the fatigued state would not differ between these muscles, even though the TA muscle has 50% relatively more slow fibers than the QF muscle relative to each muscle's overall composition. Subjects. Ten recreationally active men with no history of lower-extremity pathology participated in the study (mean age=25 years, SD=4, range=19–31; mean height=179 cm, SD=5, range=170–188; mean body mass=80 kg, SD=15, range=63–111). Methods. The subjects' TA and QF muscles were stimulated with CFTs (six 200-microsecond square waves separated by 70 milliseconds) or VFTs (first interpulse interval=5 milliseconds) that evoked an isometric contraction. Results. After potentiation, the torque-time integral and peak torque were not different for the VFT and CFT stimulation. Rise time was longer for the TA muscle than for the QF muscle and for CFT stimulation versus VFT stimulation (both approximately 40%). After 180 CFTs (50% duty cycle), peak torque decreased 56% overall, with no differences between muscles. Enhancement of the torque-time integral (25%) by VFT stimulation was not different between fatigued QF and TA muscles. Torque augmentation was due to the VFT stimulation evoking 27% greater peak torque and less slowing of rise time than the CFT stimulation (15% versus 30%). Discussion and Conclusion. The results indicate that the QF muscle may not necessarily fatigue more than the TA muscle. The results suggest that VFTs augment the force of fatigued, human skeletal muscle irrespective of fiber type.

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Megeney, L. A., P. D. Neufer, G. L. Dohm, M. H. Tan, C. A. Blewett, G. C. Elder y A. Bonen. "Effects of muscle activity and fiber composition on glucose transport and GLUT-4". American Journal of Physiology-Endocrinology and Metabolism 264, n.º 4 (1 de abril de 1993): E583—E593. http://dx.doi.org/10.1152/ajpendo.1993.264.4.e583.

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We examined glucose uptake and GLUT-4 in rat muscles [soleus (Sol), plantaris (PL), extensor digitorum longus (EDL), tibialis anterior, and the red and white gastrocnemius (WG)]. In the normally innervated perfused rat hindlimb muscles the proportion of oxidative fibers was highly correlated with the muscle's insulin-stimulated 3-O-methyl-D-glucose (3-MG) uptake (R2 = 0.78) and GLUT-4 content (r = 0.94). Insulin-stimulated 3-MG uptake and GLUT-4 were also highly correlated (R2 = 0.996). In 3-day denervated muscles, insulin-stimulated 3-MG uptake was reduced in all six muscles (-41 to -14.6%, P < 0.05), and GLUT-4 content was also reduced (-87.5 to -34.9%), except in the WG and EDL (P > 0.05). A very high correlation was observed between the decrements in GLUT-4 (%) and the decrements in 3-MG uptake (%; r = 0.99). The relatively greater loss in muscle activity (%) due to denervation in the Sol compared with the PL coincided with the reductions (%) in GLUT-4 and 3-MG uptake. These studies demonstrate that glucose uptake and GLUT-4 are regulated by insulin-independent means, namely the oxidative capacity of the muscle and the normal activity level of the muscle.

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Suriyut, Janyaruk, Satoru Muro, Phichaya Baramee, Masayo Harada y Keiichi Akita. "Various significant connections of the male pelvic floor muscles with special reference to the anal and urethral sphincter muscles". Anatomical Science International 95, n.º 3 (23 de diciembre de 2019): 305–12. http://dx.doi.org/10.1007/s12565-019-00521-2.

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AbstractThe male pelvic floor is a complex structure formed by several muscles. The levator ani muscle and the perineal muscles are important components of the pelvic floor. The perineal muscles comprise the external anal sphincter, bulbospongiosus, superficial transverse perineal muscles, and ischiocavernosus. Although the connections of the muscles of the pelvic floor have been reported recently, the anatomical details of each muscle remain unclear. In this study, we examined the male pelvic floor to clarify the connection between the muscles related to function. Fifteen male pelvises were used for microscopic dissection, and three male pelvises were used for histological examination. On the lateral aspect, the perineal muscles were connected to each other. Bundles of the levator ani muscle extended to connect to the perineal muscles. In addition, the extended muscle bundle from the levator ani muscle and the perineal muscles surround the external urethral sphincter. On the medial aspect, the levator ani muscle and the external anal sphincter form the anterior and posterior muscular slings of the anal canal. The connection between the perineal muscles and levator ani muscle indicates a possible close relationship between the functions of the urethra and anus.

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20

Fice, Jason B., Gunter P. Siegmund y Jean-Sébastien Blouin. "Neck muscle biomechanics and neural control". Journal of Neurophysiology 120, n.º 1 (1 de julio de 2018): 361–71. http://dx.doi.org/10.1152/jn.00512.2017.

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The mechanics, morphometry, and geometry of our joints, segments, and muscles are fundamental biomechanical properties intrinsic to human neural control. The goal of our study was to investigate whether the biomechanical actions of individual neck muscles predict their neural control. Specifically, we compared the moment direction and variability produced by electrical stimulation of a neck muscle (biomechanics) to the preferred activation direction and variability (neural control). Subjects sat upright with their head fixed to a six-axis load cell and their torso restrained. Indwelling wire electrodes were placed into the sternocleidomastoid (SCM), splenius capitis (SPL), and semispinalis capitis (SSC) muscles. The electrically stimulated direction was defined as the moment direction produced when a current (2–19 mA) was passed through each muscle’s electrodes. Preferred activation direction was defined as the vector sum of the spatial tuning curve built from root mean squared electromyogram when subjects produced isometric moments at 7.5% and 15% of their maximum voluntary contraction (MVC) in 26 three-dimensional directions. The spatial tuning curves at 15% MVC were well defined (unimodal, P < 0.05), and their preferred directions were 23°, 39°, and 21° different from their electrically stimulated directions for the SCM, SPL, and SSC, respectively ( P < 0.05). Intrasubject variability was smaller in electrically stimulated moment directions compared with voluntary preferred directions, and intrasubject variability decreased with increased activation levels. Our findings show that the neural control of neck muscles is not based solely on optimizing individual muscle biomechanics but, as activation increases, biomechanical constraints in part dictate the activation of synergistic neck muscles. NEW & NOTEWORTHY Biomechanics are an intrinsic part of human neural control. In this study, we found that the biomechanics of individual neck muscles cannot fully predict their neural control. Consequently, physiologically based computational neck muscle controllers cannot calculate muscle activation schemes based on the isolated biomechanics of muscles. Furthermore, by measuring biomechanics we showed that the intrasubject variability of the neural control was lower for electrical vs. voluntary activation of the neck muscles.

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21

Bonen, A., M. G. Clark y E. J. Henriksen. "Experimental approaches in muscle metabolism: hindlimb perfusion and isolated muscle incubations". American Journal of Physiology-Endocrinology and Metabolism 266, n.º 1 (1 de enero de 1994): E1—E16. http://dx.doi.org/10.1152/ajpendo.1994.266.1.e1.

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The perfusion of rat hindlimb muscles and the isolated in vitro muscle preparation are usually the preferred methods for investigating muscle metabolism. In light of recent concerns about the incubated muscle preparation, we have examined the problems, the advantages, and the viability of these two experimental techniques, with focus on glucose metabolism. A major advantage of the hindlimb perfusion system is that it maintains its metabolic viability very well, and perfusions in resting muscles can be achieved successfully with cell-free media. However, variations in the perfused rat hindlimb procedures result in considerable differences in perfusate flow among muscles, making quantitative comparisons among perfusion procedures difficult. Metabolic viability has been identified as a problem in some isolated in vitro muscle preparations. We have provided criteria to avoid muscle hypoxia. Minimum levels of insulin seem to be a key requirement to maintaining the muscle's viability, and essential amino acids are required to retard an increase in the basal rate of glucose and amino acid uptake. Under such conditions metabolic viability can be maintained during prolonged incubations (9-30 h). Both the isolated in vitro muscle preparation and the hindlimb perfusion preparation are viable models for the study of muscle metabolism.

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22

Full, R. J., D. R. Stokes, A. N. Ahn y R. K. Josephson. "Energy absorption during running by leg muscles in a cockroach". Journal of Experimental Biology 201, n.º 7 (1 de abril de 1998): 997–1012. http://dx.doi.org/10.1242/jeb.201.7.997.

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Biologists have traditionally focused on a muscle's ability to generate power. By determining muscle length, strain and activation pattern in the cockroach Blaberus discoidalis, we discovered leg extensor muscles that operate as active dampers that only absorb energy during running. Data from running animals were compared with measurements of force and power production of isolated muscles studied over a range of stimulus conditions and muscle length changes.We studied the trochanter-femoral extensor muscles 137 and 179, homologous leg muscles of the mesothoracic and metathoracic legs, respectively. Because each of these muscles is innervated by a single excitatory motor axon, the activation pattern of the muscle could be defined precisely. Work loop studies using sinusoidal strains at 8 Hz showed these trochanter-femoral extensor muscles to be quite capable actuators, able to generate a maximum of 19-25 W kg-1 (at 25 degreesC). The optimal conditions for power output were four stimuli per cycle (interstimulus interval 11 ms), a strain of approximately 4 %, and a stimulation phase such that the onset of the stimulus burst came approximately half-way through the lengthening phase of the cycle. High-speed video analysis indicated that the actual muscle strain during running was 12 % in the mesothoracic muscles and 16 % in the metathoracic ones. Myographic recordings during running showed on average 3-4 muscle action potentials per cycle, with the timing of the action potentials such that the burst usually began shortly after the onset of shortening. Imposing upon the muscle in vitro the strain, stimulus number and stimulus phase characteristic of running generated work loops in which energy was absorbed (-25 W kg-1) rather than produced. Simulations exploring a wide parameter space revealed that the dominant parameter that determines function during running is the magnitude of strain. Strains required for the maximum power output by the trochanter-femoral extensor muscles simply do not occur during constant, average-speed running. Joint angle ranges of the coxa-trochanter-femur joint during running were 3-4 times greater than the changes necessary to produce maximum power output. None of the simulated patterns of stimulation or phase resulted in power production when strain magnitude was greater than 5 %. The trochanter-femoral extensor muscles 137/179 of a cockroach running at its preferred speed of 20 cm s-1 do not operate under conditions which maximize either power output or efficiency. In vitro measurements, however, demonstrate that these muscles absorb energy, probably to provide control of leg flexion and to aid in its reversal.

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23

Velten, Brandy P. y Kenneth C. Welch. "Myosin heavy-chain isoforms in the flight and leg muscles of hummingbirds and zebra finches". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 306, n.º 11 (1 de junio de 2014): R845—R851. http://dx.doi.org/10.1152/ajpregu.00041.2014.

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Myosin heavy chain (MHC) isoform complement is intimately related to a muscle's contractile properties, yet relatively little is known about avian MHC isoforms or how they may vary with fiber type and/or the contractile properties of a muscle. The rapid shortening of muscles necessary to power flight at the high wingbeat frequencies of ruby-throated hummingbirds and zebra finches (25–60 Hz), along with the varied morphology and use of the hummingbird hindlimb, provides a unique opportunity to understand how contractile and morphological properties of avian muscle may be reflected in MHC expression. Isoforms of the hummingbird and zebra finch flight and hindlimb muscles were electrophoretically separated and compared with those of other avian species representing different contractile properties and fiber types. The flight muscles of the study species operate at drastically different contraction rates and are composed of different histochemically defined fiber types, yet each exhibited the same, single MHC isoform corresponding to the chicken adult fast isoform. Thus, despite quantitative differences in the contractile demands of flight muscles across species, this isoform appears necessary for meeting the performance demands of avian powered flight. Variation in flight muscle contractile performance across species may be due to differences in the structural composition of this conserved isoform and/or variation within other mechanically linked proteins. The leg muscles were more varied in their MHC isoform composition across both muscles and species. The disparity in hindlimb MHC expression between hummingbirds and the other species highlights previously observed differences in fiber type composition and thrust production during take-off.

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24

Frueh, Bartley R., Paul Gregorevic, David A. Williams y Gordon S. Lynch. "Specific Force of the Rat Extraocular Muscles, Levator and Superior Rectus, Measured In Situ". Journal of Neurophysiology 85, n.º 3 (1 de marzo de 2001): 1027–32. http://dx.doi.org/10.1152/jn.2001.85.3.1027.

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Extraocular muscles are characterized by their faster rates of contraction and their higher resistance to fatigue relative to limb skeletal muscles. Another often reported characteristic of extraocular muscles is that they generate lower specific forces ( sP o, force per muscle cross-sectional area, kN/m2) than limb skeletal muscles. To investigate this perplexing issue, the isometric contractile properties of the levator palpebrae superioris (levator) and superior rectus muscles of the rat were examined in situ with nerve and blood supply intact. The extraocular muscles were attached to a force transducer, and the cranial nerves exposed for direct stimulation. After determination of optimal muscle length ( L o) and stimulation voltage, a full frequency-force relationship was established for each muscle. Maximum isometric tetanic force ( P o) for the levator and superior rectus muscles was 177 ± 13 and 280 ± 10 mN (mean ± SE), respectively. For the calculation of specific force, a number of rat levator and superior rectus muscles were stored in a 20% nitric acid-based solution to isolate individual muscle fibers. Muscle fiber lengths ( L f) were expressed as a percentage of overall muscle length, allowing a mean L f to L o ratio to be used in the estimation of muscle cross-sectional area. Mean L f: L owas determined to be 0.38 for the levator muscle and 0.45 for the superior rectus muscle. The sP o for the rat levator and superior rectus muscles measured in situ was 275 and 280 kN/m2, respectively. These values are within the range of sP o values commonly reported for rat skeletal muscles. Furthermore P o and sP o for the rat levator and superior rectus muscles measured in situ were significantly higher ( P < 0.001) than P oand sP o for these muscles measured in vitro. The results indicate that the force output of intact extraocular muscles differs greatly depending on the mode of testing. Although in vitro evaluation of extraocular muscle contractility will continue to reveal important information about this group of understudied muscles, the lower sP o values of these preparations should be recognized as being significantly less than their true potential. We conclude that extraocular muscles are not intrinsically weaker than skeletal muscles.

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25

Dakin, Christopher J., John Timothy Inglis, Romeo Chua y Jean-Sébastien Blouin. "Muscle-specific modulation of vestibular reflexes with increased locomotor velocity and cadence". Journal of Neurophysiology 110, n.º 1 (1 de julio de 2013): 86–94. http://dx.doi.org/10.1152/jn.00843.2012.

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Vestibular information is one of the many sensory signals used to stabilize the body during locomotion. When locomotor velocity increases, the influence of these signals appears to wane. It is unclear whether vestibular signals are globally attenuated with velocity or are influenced by factors such as whether a muscle is contributing to balance control. Here we investigate how vestibular sensory signals influence muscles of the leg during locomotion and what causes their attenuation with increasing locomotor velocity. We hypothesized that 1) vestibular signals influence the activity of all muscles engaged in the maintenance of medio-lateral stability during locomotion and 2) increases in both cadence and velocity would be associated with attenuation of these signals. We used a stochastic vestibular stimulus and recorded electromyographic signals from muscles of the ankle, knee, and hip. Participants walked using two cadences (52 and 78 steps/min) and two walking velocities (0.4 and 0.8 m/s). We observed phase-dependent modulation of vestibular influence over ongoing muscle activity in all recorded muscles. Within a stride, reversals of the muscle responses were observed in the biceps femoris, tibialis anterior, and rectus femoris. Vestibular-muscle coupling decreases with increases in both cadence and walking velocity. These results show that the observed vestibular suppression is muscle- and phase dependent. We suggest that the phase- and muscle-specific influence of vestibular signals on locomotor activity is organized according to each muscle's functional role in body stabilization during locomotion.

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26

Dolan, Martine, Michael Patetta, Sonia Pradhan, Danil Rybalko, Aimee Bobko, Lewis Shi, Benjamin Goldberg, Farid Amirouche y Jason Koh. "Muscle Fiber Contribution to Rotator Cuff Moment Arms During Abduction for Intact Rotator Cuff, Complete Supraspinatus Tear, Superior Capsular Reconstruction, and Reverse Shoulder Arthroplasty. (225)". Orthopaedic Journal of Sports Medicine 9, n.º 10_suppl5 (1 de octubre de 2021): 2325967121S0033. http://dx.doi.org/10.1177/2325967121s00333.

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Objectives: The Rotator Cuff (RC) is formed from the subscapularis, supraspinatus, infraspinatus, and teres minor muscles and their tendinous extensions. The 4 RC tendons insert on the humeral head such that they contribute to the dynamic stability of the glenohumeral joint along with their rotational actions on the shoulder. The moment arm can be used to demonstrate the work effort potential that a specific muscle is contributing to a musculoskeletal joint rotation. The objective of this study was to break out RC muscles into multiple fibers, providing more clarity as to how individual fibers contribute to a muscle’s overall moment arm during abduction. The aims of this study are: 1.) to illustrate within each RC muscle how multiple muscle fiber lines of action work together to produce abduction in an intact shoulder 2.) to estimate the moment arm changes that take place when the intact rotator cuff goes through surgical repair with either SCR or RSA after complete supraspinatus tear. We hypothesized that the rotator cuff muscles work differently and in combination at the fiber level to bring about a resultant movement that can be assessed through the proposed method of moment arm calculation for intact RC, complete supraspinatus tear, SCR and RSA. Methods: Five fresh cadaveric shoulder specimens were used in an apparatus where each muscle was maintained in tension with the line of action towards its origin on the scapula (Figure 1). An Optotrack camera kept track of digitized points along both the origin and insertion of the rotator cuff muscles as the shoulder was abducted. Using these digitized points, multiple lines of action were created across the breadth of each muscle. Each muscle force action line was then used to calculate moment arm values during 0-90º abduction (Figure 2). Results: Moment arms calculated for multiple fiber lines spanning the tendon attachment site displayed the variance of fiber contribution and function within each muscle during abduction. Our results indicate that rather than providing a return to anatomical shoulder muscle function, RSA and SCR models produce moment arms that vary between muscles, with some contributing more to abduction and some contributing less. Highlighted below are the infraspinatus results for moment arms of individual fiber lines of action (Figure 3) and calculated mean moment arms (Figure 4) over abduction.ANOVA testing demonstrated a significant difference (p<0.001) when analyzing moment arms of intact, complete supraspinatus tear, SCR, and RSA models in teres minor and infraspinatus. There was no significant difference in moment arm values between the models in the subscapularis (p=0.148). Highlighted in Table 1 are the ANOVA testing results for infraspinatus. Conclusions: Our biomechanical analysis demonstrated sufficient sensitivity to detect differences in moment arms of the four rotator cuff muscles across a variety of models, suggesting changes to even one muscle of the shoulder will have significant implications on the function of other shoulder muscles. Furthermore, our analysis of fiber divisions within the same muscle illustrates the complex nature of the shoulder muscles themselves, and future studies should aim to better explore and model their function. The calculated percent differences from intact beautifully illustrated this complexity, as corrective RSA and SCR procedures provided better resemblance of intact anatomy within some rotator cuff muscles while creating a larger percent difference in other muscle groups. By breaking out RC muscles into multiple fibers, more clarity can be gained as to how individual fibers contribute to a muscle’s overall moment arm during abduction. This may further aid surgical decision-making, specifically for RSA where there is continued debate about whether to reconstruct portions of the RC. Given that the supraspinatus tendon is the most frequently torn tendon in the rotator cuff, especially for athletes who apply repetitive stress to the tendon, the results of this study may help inform post-operative rehabilitation by illustrating how abduction and stability are achieved after SCR and RSA.

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27

Gillis, G. B. "Neuromuscular control of anguilliform locomotion: patterns of red and white muscle activity during swimming in the american eel anguilla rostrata". Journal of Experimental Biology 201, n.º 23 (1 de diciembre de 1998): 3245–56. http://dx.doi.org/10.1242/jeb.201.23.3245.

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Two areas that have received substantial attention in investigations of muscle activity during fish swimming are (1) patterns of fiber type recruitment with swimming speed and (2) the timing of muscle activation in relation to muscle strain. Currently, very little is known about either of these areas in eels, which represent an extreme body form among fishes and utilize a mode of locomotion found at one end of the undulatory spectrum(anguilliform locomotion). To assess how this swimming mode and body form influence the neuromuscular control of swimming, I recorded electromyographic data from red and white muscle at four positions, 0.3L,0.45L, 0.6L and 0.75L, where L is body length, in eels (Anguilla rostrata)simultaneously video-taped (250 fields s-1) swimming at three speeds, 0.5,0.75 and 1.0 L s-1. As in other fish, exclusively red muscle is used at slow swimming speeds and white muscle is additionally recruited at higher swimming speeds. However, this study also revealed a novel posterior-to-anterior pattern of muscle recruitment with increasing swimming speed. At slow speeds, anteriorly located muscles are never active, muscle strain is negligible and forward thrust must be generated by posterior muscles. As speed increases, more anterior muscles are additionally recruited. Electromyogram (EMG) burst durations typically occupy between 0.2 and 0.3 undulatory cycles, irrespective of speed or position. EMG burst intensity increases significantly with swimming speed. The onset of EMG activity typically occurred near the end of muscle lengthening, whereas the offset of EMG activity occurred during shortening(typically before the muscle's return to resting length). There was a significant shift in red muscle onset times such that anterior muscles were typically active later in their strain cycle than posterior muscles. When red muscle activity patterns across various fish taxa are compared,differences in propulsive wavelength among species are related to differences in muscle activity, providing insight into the underlying neuromuscular bases of differences among undulatory swimming modes.

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28

Sink, H. y P. M. Whitington. "Early ablation of target muscles modulates the arborisation pattern of an identified embryonic Drosophila motor axon". Development 113, n.º 2 (1 de octubre de 1991): 701–7. http://dx.doi.org/10.1242/dev.113.2.701.

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The Drosophila RP3 motor axon establishes a stereotypic arborisation along the adjoining edges of muscles 6 and 7 by the end of embryogenesis. The present study has examined the role of the target muscles in determining this axonal arborisation pattern. Target muscles were surgically ablated prior to the arrival of the RP3 axon. Following further development of the embryo in culture medium, the morphology of target-deprived RP3 motor axons was assayed by intracellular injection with the dye Lucifer Yellow. Axonal arborisations were formed on a variety of non-target muscles when muscles 6 and 7 were removed and these contacts were maintained into stage 16. The pattern of axonal arborisations over non-target muscles varied between preparations in terms of the number of muscles contacted, and the distribution of arborisations on individual muscles. Following removal of muscle 6, the RP3 motor axon frequently contacted muscle 7, and axonal arborisations were present along the distal edge of the muscle. In the absence of muscle 7, the RP3 axon often did not contact muscle 6 and when muscle 6 was contacted, the arborisation of RP3 was poorly developed. Axonal processes were retained on non-target muscles when only one target muscle was present. Therefore, the establishment of a stereotypic arborisation by the RP3 motor axon is apparently dependent on growth cone contact with both target muscles.

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29

Vernooij, Carlijn A., Raymond F. Reynolds y Martin Lakie. "Physiological tremor reveals how thixotropy adapts skeletal muscle for posture and movement". Royal Society Open Science 3, n.º 5 (mayo de 2016): 160065. http://dx.doi.org/10.1098/rsos.160065.

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People and animals can move freely, but they must also be able to stay still. How do skeletal muscles economically produce both movement and posture? Humans are well known to have motor units with relatively homogeneous mechanical properties. Thixotropic muscle properties can provide a solution by providing a temporary stiffening of all skeletal muscles in postural conditions. This stiffening is alleviated almost instantly when muscles start to move. In this paper, we probe this behaviour. We monitor both the neural input to a muscle, measured here as extensor muscle electromyography (EMG), and its output, measured as tremor (finger acceleration). Both signals were analysed continuously as the subject made smooth transitions between posture and movement. The results showed that there were marked changes in tremor which systematically increased in size and decreased in frequency as the subject moved faster. By contrast, the EMG changed little and reflected muscle force requirement rather than movement speed. The altered tremor reflects naturally occurring thixotropic changes in muscle behaviour. Our results suggest that physiological tremor provides useful and hitherto unrecognized insights into skeletal muscle's role in posture and movement.

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30

Czerwinski, S. M., T. G. Kurowski, T. M. O'Neill y R. C. Hickson. "Initiating regular exercise protects against muscle atrophy from glucocorticoids". Journal of Applied Physiology 63, n.º 4 (1 de octubre de 1987): 1504–10. http://dx.doi.org/10.1152/jappl.1987.63.4.1504.

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This study was undertaken to examine whether exercise can prevent glucocorticoid-induced muscle atrophy in previously untrained individuals and to evaluate whether the time of hormone administration is a determinant in the muscle's response to glucocorticoids. Female rats were divided into five groups: 1) a sedentary group that received cortisol acetate (CA, 100 mg/kg body wt); 2) a sedentary group that received the dosing vehicle (1% aqueous carboxymethyl cellulose); 3) an exercise group that received CA immediately after each exercise session; 4) an exercise group that received CA 90 min after each exercise session; and 5) an exercise group that received the vehicle. Steroid treatment and exercise (28.7 m/min for 90 min/day) were performed for 11 consecutive days. Initiation of training prevented muscle mass loss by 60% in plantaris (P) muscles and by 25% in gastrocnemius (G) muscles. Time of steroid injection was not related to the muscle sparing response. In the glucocorticoid-treated exercised rats, the activities of citrate synthase, a training marker, increased 60% in P and 37% in G. Thus the exercise appeared to cause a greater recruitment of P muscles. These data support the hypothesis that entering into an exercise program can be effective in retarding glucocorticoid-induced muscle atrophy. The degree of atrophy prevention, however, may be related to the extent that specific muscles are recruited during exercise.

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31

Potekhina, Yu P., Е. М. Timanin y А. Е. Kantinov. "Viscoelastic properties of tissues and changes in them after osteopathic correction". Russian Osteopathic Journal, n.º 1-2 (8 de agosto de 2018): 38–45. http://dx.doi.org/10.32885/2220-0975-2018-1-2-38-45.

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Introduction. Objective measurement of the muscle tone, especially on speciﬁ c areas, represents a serious clinical issue. The most objective and well-known method for studying muscular function is electromyography. A non-invasive assessment of muscle tone and rigidity is possible by using Myoton digital palpation device. However, these methods have a range of disadvantages, which disable them to be widely used for dynamic evaluation of muscles’ viscoelastic properties during treatment, including after osteopathic correction.Goal of research - to evaluate the viscoelastic properties of tissues using palpation and instrumental techniques before and after osteopathic correction.Materials and methods. 14 students (7 practicing sports and 7 not practicing sports) aged 18-23 without problems with the musculoskeletal system were examined. Osteopathic diagnostics and measurement of viscoelastic properties of muscles before and after osteopathic correction were performed by vibrational viscoelastometry.The results. The elasticity in sportsmen’s muscles is higher compared to the elasticity of muscles of those who do not practice sports (p=0,04). Viscosity comparison did not show any difference (p=0,6). In the non-practicing sports group, the osteopathic treatment decreased muscle elasticity (p=0,000002), that may indicate their relaxation. At the same time, the viscosity was practically unchanged (p=0,45). In the sports-practicing group the elasticity and the viscosity of the muscles increased after the osteopathic correction session (p=0,0000002 and p=0,001, respectively). In the same group, two weeks after the ﬁ rst session, muscle elasticity decreased (p=0,02) and the viscosity increased (p=0,03). These changes may be considered as favorable. After the second session of osteopathic correction, the elasticity decreased even more (p=0,04), which means that muscles became relaxed.Conclusions. Therefore, reported results showed that the viscoelastometry method had a real potential for an objective evaluation of the skeletal muscles’ condition and the effects of osteopathic treatment. Modiﬁ cations in the viscoelastic properties of the tissues demonstrate that the effects of osteopathic treatment are ambiguous and depend on the initial muscle’s condition.

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32

Semariasih, Ni Komang Dewi, Ni Luh Nopi Andayani y I. Made Muliarta. "THE CORELATION BETWEEN GRIP MUSCLES’ STRENTGH AND A LEVEL OF FUNCTIONAL ABILITY AMONG THE ELDERLY WOMEN IN TISTA KERAMBITAN, TABANAN". Majalah Ilmiah Fisioterapi Indonesia 7, n.º 2 (15 de mayo de 2019): 40. http://dx.doi.org/10.24843/mifi.2019.v07.i02.p11.

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The aging process affects the skeletal muscle structure and disability of the musculoskeletal system which resulted in limited and slowed motion. One characteristic of the aging process is a decrease in muscle strength. Muscle strength affects almost all daily activity. Decreased muscle strength can lead to limitations in daily activities, independence and quality of life. This study aims to determine the relationship between handgrip muscles’ strength and level of functional ability among elderly women in Tista, Kerambitan Tabanan. To assess the strength of the relationship and assess the direction of the relationship between the variables. The research design was used cross sectional study with Simple Random Sampling and got 73 samples. The strength of handgrip muscles was measured using Hand-grip dynamometer, while the functional independence level was assessed by Intermediate Activity Daily Living (IADL) questionnaire interview. Result of research by using Spearman correlation test got value P = 0,000 (P <0,05) and Coefficient correlation value equal to 0,489 indicate that there is a significant correlation between handgrip muscles’ strength with functional ability independence level, this relation is positive and medium. In conculsion that handgrip muscles’s strength and level of functional ability are positively correlated and medium. The stronger the muscle strength of the handgrip, the higher the level of functional ability independence and vice versa. Therefore, handgrip muscle’s strength can be used in identifying disabilities in the elderly. Keywords: elderly, handgrip muscles’ strength, functional capabilities, disability.

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33

Sulbarán, Guidenn, Lorenzo Alamo, Antonio Pinto, Gustavo Márquez, Franklin Méndez, Raúl Padrón y Roger Craig. "An invertebrate smooth muscle with striated muscle myosin filaments". Proceedings of the National Academy of Sciences 112, n.º 42 (6 de octubre de 2015): E5660—E5668. http://dx.doi.org/10.1073/pnas.1513439112.

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Muscle tissues are classically divided into two major types, depending on the presence or absence of striations. In striated muscles, the actin filaments are anchored at Z-lines and the myosin and actin filaments are in register, whereas in smooth muscles, the actin filaments are attached to dense bodies and the myosin and actin filaments are out of register. The structure of the filaments in smooth muscles is also different from that in striated muscles. Here we have studied the structure of myosin filaments from the smooth muscles of the human parasite Schistosoma mansoni. We find, surprisingly, that they are indistinguishable from those in an arthropod striated muscle. This structural similarity is supported by sequence comparison between the schistosome myosin II heavy chain and known striated muscle myosins. In contrast, the actin filaments of schistosomes are similar to those of smooth muscles, lacking troponin-dependent regulation. We conclude that schistosome muscles are hybrids, containing striated muscle-like myosin filaments and smooth muscle-like actin filaments in a smooth muscle architecture. This surprising finding has broad significance for understanding how muscles are built and how they evolved, and challenges the paradigm that smooth and striated muscles always have distinctly different components.

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34

Vignaud, A., C. Hourde, F. Medja, O. Agbulut, G. Butler-Browne y A. Ferry. "Impaired Skeletal Muscle Repair after Ischemia-Reperfusion Injury in Mice". Journal of Biomedicine and Biotechnology 2010 (2010): 1–10. http://dx.doi.org/10.1155/2010/724914.

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Ischemia/reperfusion (IR) injury can induce skeletal muscle fibre death and subsequent regeneration. By 14 days, absolute and specific maximal forces and fatigue resistance in ischemic/reperfused soleus muscles were still reduced (−89%, −81%, and −75%, resp.) as compared to control muscles (P<.05). The decrease of these parameters in ischemic/reperfused muscle was much greater than that of myotoxic injured muscles (−12%, −11%, and −19%;P<.05). In addition, at 14 days ischemic/reperfused muscle structure was still abnormal, showing small muscle fibres expressing neonatal myosin heavy chain and large necrotic muscle fibres that were not observed in myotoxin treated muscles. By 56 days, in contrast to myotoxin treated muscles, specific maximal force and muscle weight of the ischemic/reperfused muscles did not fully recover (P<.05). This differential recovery between ischemic/reperfused and myotoxin treated muscles was not related to the differences in the initial cell death, loss of satellite cells after injury, expression of growth factors (IGF1, IGF2..), or capillary density in regenerating muscles. In conclusion, our results demonstrate that IR injury in mice induces long term detrimental effects in skeletal muscles and that the recovery following IR injury was delayed for yet unknown reasons as compared to myotoxic injury.

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35

Tiwari, Rashi, Michael A. Meller, Karl B. Wajcs, Caris Moses, Ismael Reveles y Ephrahim Garcia. "Hydraulic artificial muscles". Journal of Intelligent Material Systems and Structures 23, n.º 3 (febrero de 2012): 301–12. http://dx.doi.org/10.1177/1045389x12438627.

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This article presents hydraulic artificial muscles as a viable alternative to pneumatic artificial muscles. Despite the actuation mechanism being similar to its pneumatic counterpart, hydraulic artificial muscles have not been widely studied. Hydraulic artificial muscles offer all the same advantages of pneumatic artificial muscles, such as compliance, light weight, low maintenance, and low cost, when compared to traditional fluidic cylinder actuators. Muscle characterization in isometric and isobaric conditions are discussed and compared to pneumatic artificial muscles. A quasi-static model incorporating the effect of mesh angle, friction, and muscle volume change throughout actuation is presented. This article also discusses the use of hydraulic artificial muscles for low-pressure hydraulic mesoscale robotic leg.

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Porter, J. D., J. A. Rafael, R. J. Ragusa, J. K. Brueckner, J. I. Trickett y K. E. Davies. "The sparing of extraocular muscle in dystrophinopathy is lost in mice lacking utrophin and dystrophin". Journal of Cell Science 111, n.º 13 (1 de julio de 1998): 1801–11. http://dx.doi.org/10.1242/jcs.111.13.1801.

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The extraocular muscles are one of few skeletal muscles that are structurally and functionally intact in Duchenne muscular dystrophy. Little is known about the mechanisms responsible for differential sparing or targeting of muscle groups in neuromuscular disease. One hypothesis is that constitutive or adaptive properties of the unique extraocular muscle phenotype may underlie their protection in dystrophinopathy. We assessed the status of extraocular muscles in the mdx mouse model of muscular dystrophy. Mice showed mild pathology in accessory extraocular muscles, but no signs of pathology were evident in the principal extraocular muscles at any age. By immunoblotting, the extraocular muscles of mdx mice exhibited increased levels of a dystrophin analog, dystrophin-related protein or utrophin. These data suggest, but do not provide mechanistic evidence, that utrophin mediates eye muscle protection. To examine a potential causal relationship, knockout mouse models were used to determine whether eye muscle sparing could be reversed. Mice lacking expression of utrophin alone, like the dystrophin-deficient mdx mouse, showed no pathological alterations in extraocular muscle. However, mice deficient in both utrophin and dystrophin exhibited severe changes in both the accessory and principal extraocular muscles, with the eye muscles affected more adversely than other skeletal muscles. Selected extraocular muscle fiber types still remained spared, suggesting the operation of an alternative mechanism for muscle sparing in these fiber types. We propose that an endogenous upregulation of utrophin is mechanistic in protecting extraocular muscle in dystrophinopathy. Moreover, data lend support to the hypothesis that interventions designed to increase utrophin levels may ameliorate the pathology in other skeletal muscles in Duchenne muscular dystrophy.

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Oas, Sandy T., Anton L. Bryantsev y Richard M. Cripps. "Arrest is a regulator of fiber-specific alternative splicing in the indirect flight muscles of Drosophila". Journal of Cell Biology 206, n.º 7 (22 de septiembre de 2014): 895–908. http://dx.doi.org/10.1083/jcb.201405058.

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Drosophila melanogaster flight muscles are distinct from other skeletal muscles, such as jump muscles, and express several uniquely spliced muscle-associated transcripts. We sought to identify factors mediating splicing differences between the flight and jump muscle fiber types. We found that the ribonucleic acid–binding protein Arrest (Aret) is expressed in flight muscles: in founder cells, Aret accumulates in a novel intranuclear compartment that we termed the Bruno body, and after the onset of muscle differentiation, Aret disperses in the nucleus. Down-regulation of the aret gene led to ultrastructural changes and functional impairment of flight muscles, and transcripts of structural genes expressed in the flight muscles became spliced in a manner characteristic of jump muscles. Aret also potently promoted flight muscle splicing patterns when ectopically expressed in jump muscles or tissue culture cells. Genetically, aret is located downstream of exd (extradenticle), hth (homothorax), and salm (spalt major), transcription factors that control fiber identity. Our observations provide insight into a transcriptional and splicing regulatory network for muscle fiber specification.

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38

Donovan, C. M. y J. A. Faulkner. "Plasticity of skeletal muscle: regenerating fibers adapt more rapidly than surviving fibers". Journal of Applied Physiology 62, n.º 6 (1 de junio de 1987): 2507–11. http://dx.doi.org/10.1152/jappl.1987.62.6.2507.

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The properties of mammalian skeletal muscle demonstrate a high degree of structural and functional plasticity as evidenced by their adaptability to an atypical site after cross-transplantation and to atypical innervation after cross-innervation. We tested the hypothesis that, regardless of fiber type, skeletal muscles composed of regenerating fibers adapt more readily than muscles composed of surviving fibers when placed in an atypical site with atypical innervation. Fast muscles of rats were autografted into the site of slow muscles or vice versa with the donor muscle innervated by the motor nerve to the recipient site. Surviving fibers in donor muscles were obtained by grafting with vasculature intact (vascularized muscle graft), and regenerating fibers were obtained by grafting with vasculature severed (free muscle graft). Our hypothesis was supported because 60 days after grafting, transposed muscles with surviving fibers demonstrated only a slight change from the contractile properties and fiber typing of donor muscles, whereas transplanted muscles with regenerating fibers demonstrated almost complete change to those of the muscle formerly in the atypical site.

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Zieliński, Grzegorz, Anna Matysik-Woźniak, Anna Pankowska, Radosław Pietura, Robert Rejdak y Kamil Jonak. "High Myopia and Thickness of Extraocular and Masticatory Muscles—7T MRI, Preliminary Study". Journal of Clinical Medicine 12, n.º 12 (20 de junio de 2023): 4166. http://dx.doi.org/10.3390/jcm12124166.

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(1) Background: Myopia is one of the most common refractive errors in the world. The aim of this study was to evaluate the transverse dimensions of selected masticatory muscles (temporalis muscle and masseter muscle) versus the transverse dimensions of selected extraocular muscles (superior rectus, inferior rectus, medial rectus and lateral rectus) in emmetropic and high myopic subjects. (2) Methods: Twenty-seven individuals were included in the analysis, resulting in 24 eyeballs of patients with high myopia and 30 eyeballs of emmetropic subjects. A 7 Tesla resonance was used to analyze the described muscles. (3) Results: Statistical analysis showed differences in all analyzed extraocular muscles and all analyzed masticatory muscles between emmetropic subjects and high myopic subjects. In the high myopic subject group, statistical analysis showed four correlations. The three negative correlations were between the lateral rectus muscle and an axial length eyeball, refractive error and an axial length eyeball, and the inferior rectus muscle and visual acuity. The positive correlation was between the lateral rectus muscle and the medial rectus muscle. (4) Conclusions: The high myopic subjects are characterized by a larger cross-sectional area of extraocular muscles and masticatory muscles compared to the emmetropic subjects. Correlations were observed between the thickness of the extraocular muscles and the masticatory muscles. The lateral rectus muscle was related to the length of the eyeball. The phenomenon requires further study.

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40

Brookham, Rebecca L., Linda McLean y Clark R. Dickerson. "Construct Validity of Muscle Force Tests of the Rotator Cuff Muscles: An Electromyographic Investigation". Physical Therapy 90, n.º 4 (1 de abril de 2010): 572–80. http://dx.doi.org/10.2522/ptj.20090024.

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Background Manual muscle tests (MMTs) are used in clinical settings to evaluate the function and strength (force-generating capacity) of a specific muscle in a position at which the muscle is believed to be most isolated from other synergists and antagonists. Despite frequent use of MMTs, few electromyographic evaluations exist to confirm the ability of MMTs to isolate rotator cuff muscles. Objective This study examined rotator cuff isolation during 29 shoulder muscle force tests (9 clinical and 20 generic tests). Design An experimental design was used in this study. Participants and Measurements Electromyographic data were recorded from 4 rotator cuff muscles and 10 additional shoulder muscles of 12 male participants. Maximal isolation ratios (mean specific rotator cuff muscle activation to mean activation of the other 13 recorded muscles) defined which of these tests most isolated the rotator cuff muscles. Results Three rotator cuff muscles were maximally isolated (obtained highest isolation ratios) within their respective clinical test groups (lateral rotator test group for the infraspinatus and teres minor muscles and abduction test group for the supraspinatus muscle). The subscapularis muscle was maximally isolated equally as effectively within the generic ulnar force and clinical medial rotation groups. Similarly, the supraspinatus and teres minor muscles were isolated equally as effectively in some generic test groups as they were in their respective clinical test groups. Limitations Postural artifact in the wire electrodes caused exclusion of some channels from calculations. The grouping of muscle force tests based on test criteria (clinical or generic tests and muscle action) may have influenced which groups most isolated the muscle of interest. Conclusions The results confirmed the appropriateness of 9 commonly used clinical tests for isolating rotator cuff muscles, but suggested that several other muscle force tests were equally appropriate for isolating these muscles.

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van Eijden, T. M. G. J. y S. J. J. Turkawski. "Morphology and Physiology of Masticatory Muscle Motor Units". Critical Reviews in Oral Biology & Medicine 12, n.º 1 (enero de 2001): 76–91. http://dx.doi.org/10.1177/10454411010120010601.

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Motor unit territories in masticatory muscles appear to be smaller than territories in limb muscles, and this would suggest a more localized organization of motor control in masticatory muscles. Motor unit cross-sectional areas show a wide range of values, which explains the large variability of motor unit force output. The proportion of motor unit muscle fibers containing more than one myosin heavy-chain (MHC) isoform is considerably larger in masticatory muscles than in limb and trunk muscles. This explains the continuous range of contraction speeds found in masticatory muscle motor units. Hence, in masticatory muscles, a finer gradation of force and contraction speeds is possible than in limb and in trunk muscles. The proportion of slow-type motor units is relatively large in deep and anterior masticatory muscle regions, whereas more fast-type units are more common in the superficial and posterior muscle regions. Muscle portions with a high proportion of slow-type motor units are better equipped for a finer control of muscle force and a larger resistance to fatigue during chewing and biting than muscle portions with a high proportion of fast units. For the force modulation, masticatory muscles rely mostly on recruitment gradation at low force levels and on rate gradation at high force levels. Henneman's principle of an orderly recruitment of motor units has also been reported for various masticatory muscles. The presence of localized motor unit territories and task-specific motor unit activity facilitates differential control of separate muscle portions. This gives the masticatory muscles the capacity of producing a large diversity of mechanical actions. In this review, the properties of masticatory muscle motor units are discussed.

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Sun, Yunfeng, Caterina Fede, Xiaoxiao Zhao, Alessandra Del Felice, Carmelo Pirri y Carla Stecco. "Quantity and Distribution of Muscle Spindles in Animal and Human Muscles". International Journal of Molecular Sciences 25, n.º 13 (3 de julio de 2024): 7320. http://dx.doi.org/10.3390/ijms25137320.

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Muscle spindles have unique anatomical characteristics that can be directly affected by the surrounding tissues under physiological and pathological conditions. Understanding their spatial distribution and density in different muscles is imperative to unravel the complexity of motor function. In the present study, the distribution and number/density of muscle spindles in human and animal muscles were reviewed. We identified 56 articles focusing on muscle spindle distribution; 13 articles focused on human muscles and 43 focused on animal muscles. The results demonstrate that spindles are located at the nerve entry points and along distributed vessels and they relate to the intramuscular connective tissue. Muscles’ deep layers and middle segments are the main topographic distribution areas. Eleven articles on humans and thirty-three articles on animals (totaling forty-four articles) focusing on muscle spindle quantity and density were identified. Hand and head muscles, such as the pronator teres/medial pterygoid muscle/masseter/flexor digitorum, were most commonly studied in the human studies. For animals, whole-body musculature was studied. The present study summarized the spindle quantity in 77 human and 189 animal muscles. We identified well-studied muscles and any as-yet unfound data. The current data fail to clarify the relationship between quantity/density and muscle characteristics. The intricate distribution of the muscle spindles and their density and quantity throughout the body present some unique patterns or correlations, according to the current data. However, it remains unclear whether muscles with fine motor control have more muscle spindles since the study standards are inconsistent and data on numerous muscles are missing. This study provides a comprehensive and exhaustive approach for clinicians and researchers to determine muscle spindle status.

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Fernandes, J. y K. VijayRaghavan. "The development of indirect flight muscle innervation in Drosophila melanogaster". Development 118, n.º 1 (1 de mayo de 1993): 215–27. http://dx.doi.org/10.1242/dev.118.1.215.

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We have examined the development of innervation to the indirect flight muscles of Drosophila. During metamorphosis, the larval intersegmental nerve of the mesothorax is remodelled to innervate the dorsal longitudinal muscles and two of the dorsoventral muscles. Another modified larval nerve innervates the remaining dorsoventral muscle. The dorsal longitudinal muscles develop using modified larval muscles as templates while dorsoventral muscles develop without the use of such templates. The development of innervation to the two groups of indirect flight muscles differs in spatial and temporal patterns, which may reflect the different ways in which these muscles develop. The identification of myoblasts associated with thoracic nerves during larval life and the association of migrating myoblasts with nerves during metamorphosis indicate the existence of nerve-muscle interactions during indirect flight muscle development. In addition, the developing pattern of axonal branching suggests a role for the target muscles in respecifying neuromuscular junctions during metamorphosis.

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Yahya, Imadeldin, Dorit Hockman, Beate Brand-Saberi y Gabriela Morosan-Puopolo. "New Insights into the Diversity of Branchiomeric Muscle Development: Genetic Programs and Differentiation". Biology 11, n.º 8 (22 de agosto de 2022): 1245. http://dx.doi.org/10.3390/biology11081245.

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Branchiomeric skeletal muscles are a subset of head muscles originating from skeletal muscle progenitor cells in the mesodermal core of pharyngeal arches. These muscles are involved in facial expression, mastication, and function of the larynx and pharynx. Branchiomeric muscles have been the focus of many studies over the years due to their distinct developmental programs and common origin with the heart muscle. A prerequisite for investigating these muscles’ properties and therapeutic potential is understanding their genetic program and differentiation. In contrast to our understanding of how branchiomeric muscles are formed, less is known about their differentiation. This review focuses on the differentiation of branchiomeric muscles in mouse embryos. Furthermore, the relationship between branchiomeric muscle progenitor and neural crest cells in the pharyngeal arches of chicken embryos is also discussed. Additionally, we summarize recent studies into the genetic networks that distinguish between first arch-derived muscles and other pharyngeal arch muscles.

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Locke, Marius y Stephanie A. Salerno. "Ovariectomy alters lengthening contraction induced heat shock protein expression". Applied Physiology, Nutrition, and Metabolism 45, n.º 5 (mayo de 2020): 530–38. http://dx.doi.org/10.1139/apnm-2019-0212.

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Estrogen appears to play a role in minimizing skeletal muscle damage as well as regulating the expression of the protective heat shock proteins (HSPs). To clarify the relationship between estrogen, muscle HSP content, and muscle damage, tibialis anterior (TA) muscles from ovary-intact (OVI; n = 12) and ovariectomized (OVX; 3 weeks, n = 12) female Sprague–Dawley rats were subjected to either 20 or 40 lengthening contractions (LCs). Twenty-four hours after stimulation, TA muscles were removed, processed, and assessed for HSP25 and HSP72 content as well as muscle (damage) morphology. No differences in muscle contractile properties were observed in TA muscles between OVI and OVX animals for peak torque during the LCs. In unstressed TA muscles, the basal expression of HSP72 expression was decreased in OVX animals (P < 0.05) while HSP25 content remained unchanged. Following 20 LCs, HSP25 content was elevated (P < 0.05) in TA muscles from OVX animals but unchanged in muscles from OVI animals. Following 40 LCs, HSP25 content was elevated (P < 0.01) in TA muscles from both OVI and OVX animals while HSP72 content was elevated only in TA muscles from OVI animals (P < 0.05). Taken together, these data suggest the loss of ovarian hormones, such as estrogen, may impair the skeletal muscle cellular stress response thereby rendering muscles more susceptible to certain types of contraction induced damage. Novelty Ovariectomy alters muscle HSP72 content. Muscle contractile measures are maintained following ovariectomy.

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Abuwarda, Khaled y Abdel-Rahman Akl. "Changes in Electromyographic Activity of the Dominant Arm Muscles during Forehand Stroke Phases in Wheelchair Tennis". Sensors 23, n.º 20 (21 de octubre de 2023): 8623. http://dx.doi.org/10.3390/s23208623.

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The aim of this study was to determine the muscle activations of the dominant arm during the forehand stroke of wheelchair tennis. Five players participated in the present study (age: 32.6 ± 9.9 years; body mass: 63.8 ± 3.12 kg; height: 164.4 ± 1.7 cm). The electrical muscle activity of six dominant arm muscles was recorded using an sEMG system. A significant effect of the muscle’s activity was observed, and it was shown that the muscle activation was significantly higher in the execution phase compared to the preparation phase in the anterior deltoid and biceps brachii (34.98 ± 10.23% and 29.13 ± 8.27%, p < 0.001); the posterior deltoid, triceps brachii, flexor carpi radialis, and extensor carpi radialis were higher in the follow-through phase than in the execution phase (16.43 ± 11.72%, 16.96 ± 12.19%, 36.23 ± 21.47% and 19.13 ± 12.55%, p < 0.01). In conclusion, it was determined that the muscle activations of the dominant arm muscles demonstrate variances throughout the phases of the forehand stroke. Furthermore, the application of electromyographic analysis to the primary arm muscles has been beneficial in understanding the muscular activity of the shoulder, elbow, and wrist throughout the various phases of the forehand stroke in wheelchair tennis.

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Wilmink, Ronnie J. H. y T. Richard Nichols. "Distribution of Heterogenic Reflexes Among the Quadriceps and Triceps Surae Muscles of the Cat Hind Limb". Journal of Neurophysiology 90, n.º 4 (octubre de 2003): 2310–24. http://dx.doi.org/10.1152/jn.00833.2002.

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Neural signals from proprioceptors in muscles provide length and force-related linkages among muscles of the limbs. The functions of this network of heterogenic reflexes remain unclear. New data are reported here on the distribution and magnitudes of neural feedback among quadriceps and triceps surae muscles in the decerebrate cat. The purpose of this paper was to distinguish whether inhibitory-force feedback is directed against muscles by virtue of the motor-unit composition or articulation of the muscle. These studies were carried out using controlled stretches and measurements of the resulting force responses of individual quadriceps and triceps surae muscles. Responses were evoked over a wide range of background force levels. In agreement with earlier electrophysiological studies, excitatory length feedback strongly linked the vastus muscles, but excitatory reflexes between each vastus and rectus femoris muscles were weak. We also observed a substantial excitatory linkage from the vastus muscles to the soleus muscle. In contrast, force-related inhibition was absent in the heterogenic reflexes among the vastus muscles but strong and bidirectional between each vastus muscle and the rectus femoris muscle and between triceps surae and quadriceps muscles. We conclude that short-latency feedback in the hindlimb is organized according to muscle articulation. Length feedback within muscle groups regulates joint stiffness while interjoint length feedback may compensate for the effects of nonuniform inertial properties of the limb. Force feedback is organized to regulate coupling between joints and, along with length feedback, determine the mechanical properties of the endpoint.

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Baltusnikas, Juozas, Audrius Kilikevicius, Tomas Venckunas, Andrej Fokin, Arimantas Lionikas y Aivaras Ratkevicius. "Regenerated soleus muscle shows reduced creatine kinase efflux after contractile activity in vitro". Applied Physiology, Nutrition, and Metabolism 40, n.º 2 (febrero de 2015): 129–33. http://dx.doi.org/10.1139/apnm-2014-0274.

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Regenerated skeletal muscles show less muscle damage after strenuous muscle exercise. The aim of the studies was to investigate if the regeneration is associated with reduced muscle creatine kinase (CK) efflux immediately after the exercise. Cryolesion was applied to the soleus muscle of 3-month-old C57BL/6J male mice. Then total CK efflux was assessed in vitro in the regenerated muscles without exercise or after 100 eccentric contractions. The same measurements were performed in the control muscles, which were not exposed to cryolesion. Regenerated muscles generated weaker (P < 0.05) twitches, but stronger (P < 0.05) 150-Hz and 300-Hz tetani with prolonged (P < 0.01) contraction times compared with the control muscles. There was no difference between regenerated and control muscles in the total CK efflux without exercise, but only control muscles showed an increase (P < 0.001) in the CK efflux after the exercise. Our results suggest that muscle regeneration is associated with modulation of contractile properties and improvement in muscle resistance to damage after eccentric exercise.

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Bondarenko, Stanislav, Dmytro Sereda y Olena Karpinska. "THE STUDY OF THE WORK OF THE MUSCLES RESPONSIBLE FOR THE FUNCTIONALITY OF THE HIP JOINT AFTER TOTAL HIP ARTHROPLASTY USING DIFFERENT SURGICAL APPROACHES". ORTHOPAEDICS TRAUMATOLOGY and PROSTHETICS, n.º 2 (9 de julio de 2024): 24–32. http://dx.doi.org/10.15674/0030-59872024224-32.

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Muscles that can be damaged during endoprosthesis are indicated. Objective. To study the features of muscle work to ensure walking function after hip arthroplasty depending on the surgical approach. Methods. The basis of the simulation is the basic OpenSim Gate2392 model. Six models were created that predicted the condition of the muscles of the lower limb in normal conditions, during coxarthrosis and after 6 and 12 months. after surgery with lateral and anterior approaches. The results. For lateral access in 6 months. after the operation, the adductor muscles responsible for stabilizing the pelvis in the single-support phase of the step and during the transfer of the foot do not work enough, while the hip flexor muscles (in the model, the rectus femoris muscle) take over the responsibility for the step, but with overvoltage. On the contrary, with the front approach, we observe a weakening of the flexor muscles, which leads to overstrain of the gluteal muscles and hip stabilizer muscles. After 12 months, the muscle strength normalizes for most of them to 90–95 % of the norm, a 2–3 times increase in the torque of the hip flexor muscles and hip stabilizer muscles is observed. Taking a normal step causes muscle strain. During the anterior approach, the foot is transferred during the phase, that is, when most of the muscles are involved. The rectus femoris muscle, which is the strongest of the muscles discussed in the paper, does the main work of moving the foot. In the case of possible damage to the rectus muscle during anterior access, even after a year there is a violation of its work — excessive overexertion and involvement of the reserves of other muscles. Conclusions. Mathematical modeling of the work of muscles that may be damaged during hip arthroplasty surgery, conditional muscle strength for 6 months. after the operation, they are not able to develop the necessary torque to take a normal step. For muscle strength, which in the model corresponded to 12 months,the muscles are able to perform a normal function regardless of surgical access, but their overstrain is observed.

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Melnyk, O. O. y M. V. Melnyk. "Біоморфологічні особливості м’язів, діючих на плечовий суглоб, деяких представників ряду горобцеподібних – Ordо Passeriformes". Scientific Messenger of LNU of Veterinary Medicine and Biotechnologies 19, n.º 77 (7 de marzo de 2017): 55–59. http://dx.doi.org/10.15421/nvlvet7713.

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Biomorphological features of muscles that act on the shoulder joint of some representatives of orderPasseriformes are represented in the article. As shoulder joint of birds has many axes, not only the muscles of the shoulder joint provide the movements in it, but some of the muscles of the shoulder girdle and elbow joint. It should be noted that the main flight muscles of birds are the shoulder girdle muscles, including the chest (m. pectoralis) and supra-coracoid muscles. Some muscles of an elbow joint, including m. coracoradialis and m. scapuli triceps, are equally important. However, the amount of muscles that somehow act on the shoulder joint of the investigated birds' species is different, the degree of muscle development in these species is also different. In order to understand the degree of development, particularly mechanisms of differentiation and development of muscle structures, a comprehensive study of the muscles of the shoulder girdle, shoulder and elbow joints was conducted. The material for the research was obtained from the funds of the Department of animal anatomy named after acad. V.G. Kasyanenko of National University of Life and Environmental Sciences of Ukraine, where the studies of muscular structures of the shoulder joint of some representatives of order Passeriformes, including raven (Corvus corax), rook (Corvus fragilegus), waxwings (Bombycilla garrulous), were conducted. Research of muscles of the shoulder joint, shoulder girdle and elbow joint of birds was performed on fresh or fixed in 10% formalin solution cadavers. After describing and defining of fixation points of the muscles, they were dissected to determine the location of the muscle fibers. In addition, in order to determine the degree of development of muscles and muscle groups, each muscle was weighed. During the research, muscles were drawn or pictured to complement the work with illustrative material. There was no larger or smaller muscle neither in muscle group of shoulder, nor elbow joint that should be significantly for each case. There is no clear stability in the development of muscle groups of these joints. At the same time, muscle group of elbow joint is more developed than the muscle group of shoulder joint. All these mentioned features of structure and differentiation of muscles, which act on the shoulder joint of birds, are caused by physical exertion, posed by adaptation to a different type, speed and duration of flight.

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