Journal articles on the topic 'Muscle mechanics'
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Sugi, Haruo. "Muscle mechanics." Journal of Biomechanics 40 (January 2007): S2. http://dx.doi.org/10.1016/s0021-9290(07)70002-7.
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FITTS, ROBERT H., and JEFFREY J. WIDRICK. "Muscle Mechanics." Exercise and Sport Sciences Reviews 24 (1996): 427???474. http://dx.doi.org/10.1249/00003677-199600240-00016.
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Hwang, Willy, Jason C. Carvalho, Isaac Tarlovsky, and Aladin M. Boriek. "Passive mechanics of canine internal abdominal muscles." Journal of Applied Physiology 98, no. 5 (May 2005): 1829–35. http://dx.doi.org/10.1152/japplphysiol.00910.2003.
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The internal abdominal muscles are biaxially loaded in vivo, and therefore length-tension relations along and transverse to the directions of the muscle fibers are important in understanding their mechanical properties. We hypothesized that 1) internal oblique and transversus abdominis form an internal abdominal composite muscle with altered compliance than that of either muscle individually, and 2) anisotropy, different compliances in orthogonal directions, of internal abdominal composite muscle is less pronounced than that of its individual muscles. To test these hypotheses, in vitro mechanical testing was performed on 5 × 5 cm squares of transversus abdominis, internal oblique, and the two muscles together as a composite. These tissues were harvested from the left lateral side of abdominal muscles of eleven mongrel dogs (15–23 kg) and placed in a bath of oxygenated Krebs solution. Each tissue strip was attached to a biaxial mechanical testing device. Each muscle was passively lengthened and shortened along muscle fibers, transverse to fibers, or simultaneously along and transverse to muscle fibers. Both transversus abdominis and internal oblique muscles demonstrated less extensibility in the direction transverse to muscle fibers than along fibers. Biaxial loading caused a stiffening effect that was greater in the direction along the fibers than transverse to the fibers. Furthermore, the abdominal muscle composite was less compliant than either muscle alone in the direction of the muscle fibers. Taken together, our data suggested that the internal abdominal composite tissue has complex mechanical properties that are dependent on the mechanical properties of internal oblique and transversus abdominis muscles.
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Bilston, Lynne E., Bart Bolsterlee, Antoine Nordez, and Shantanu Sinha. "Contemporary image-based methods for measuring passive mechanical properties of skeletal muscles in vivo." Journal of Applied Physiology 126, no. 5 (May 1, 2019): 1454–64. http://dx.doi.org/10.1152/japplphysiol.00672.2018.
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Skeletal muscles’ primary function in the body is mechanical: to move and stabilize the skeleton. As such, their mechanical behavior is a key aspect of their physiology. Recent developments in medical imaging technology have enabled quantitative studies of passive muscle mechanics, ranging from measurements of intrinsic muscle mechanical properties, such as elasticity and viscosity, to three-dimensional muscle architecture and dynamic muscle deformation and kinematics. In this review we summarize the principles and applications of contemporary imaging methods that have been used to study the passive mechanical behavior of skeletal muscles. Elastography measurements can provide in vivo maps of passive muscle mechanical parameters, and both MRI and ultrasound methods are available (magnetic resonance elastography and ultrasound shear wave elastography, respectively). Both have been shown to differentiate between healthy muscle and muscles affected by a broad range of clinical conditions. Detailed muscle architecture can now be depicted using diffusion tensor imaging, which not only is particularly useful for computational modeling of muscle but also has potential in assessing architectural changes in muscle disorders. More dynamic information about muscle mechanics can be obtained using a range of dynamic MRI methods, which characterize the detailed internal muscle deformations during motion. There are several MRI techniques available (e.g., phase-contrast MRI, displacement-encoded MRI, and “tagged” MRI), each of which can be collected in synchrony with muscle motion and postprocessed to quantify muscle deformation. Together, these modern imaging techniques can characterize muscle motion, deformation, mechanical properties, and architecture, providing complementary insights into skeletal muscle function.
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Lopez, Michael A., Sherina Bontiff, Mary Adeyeye, Aziz I. Shaibani, Matthew S. Alexander, Shari Wynd, and Aladin M. Boriek. "Mechanics of dystrophin deficient skeletal muscles in very young mice and effects of age." American Journal of Physiology-Cell Physiology 321, no. 2 (August 1, 2021): C230—C246. http://dx.doi.org/10.1152/ajpcell.00155.2019.
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The MDX mouse is an animal model of Duchenne muscular dystrophy, a human disease marked by an absence of the cytoskeletal protein, dystrophin. We hypothesized that 1) dystrophin serves a complex mechanical role in skeletal muscles by contributing to passive compliance, viscoelastic properties, and contractile force production and 2) age is a modulator of passive mechanics of skeletal muscles of the MDX mouse. Using an in vitro biaxial mechanical testing apparatus, we measured passive length-tension relationships in the muscle fiber direction as well as transverse to the fibers, viscoelastic stress-relaxation curves, and isometric contractile properties. To avoid confounding secondary effects of muscle necrosis, inflammation, and fibrosis, we used very young 3-wk-old mice whose muscles reflected the prefibrotic and prenecrotic state. Compared with controls, 1) muscle extensibility and compliance were greater in both along fiber direction and transverse to fiber direction in MDX mice and 2) the relaxed elastic modulus was greater in dystrophin-deficient diaphragms. Furthermore, isometric contractile muscle stress was reduced in the presence and absence of transverse fiber passive stress. We also examined the effect of age on the diaphragm length-tension relationships and found that diaphragm muscles from 9-mo-old MDX mice were significantly less compliant and less extensible than those of muscles from very young MDX mice. Our data suggest that the age of the MDX mouse is a determinant of the passive mechanics of the diaphragm; in the prefibrotic/prenecrotic stage, muscle extensibility and compliance, as well as viscoelasticity, and muscle contractility are altered by loss of dystrophin.
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Jannapureddy, Suneal R., Nisha D. Patel, Willy Hwang, and Aladin M. Boriek. "Selected Contribution: Merosin deficiency leads to alterations in passive and active skeletal muscle mechanics." Journal of Applied Physiology 94, no. 6 (June 1, 2003): 2524–33. http://dx.doi.org/10.1152/japplphysiol.01078.2002.
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The role of extracellular elements on the mechanical properties of skeletal muscles is unknown. Merosin is an essential extracellular matrix protein that forms a mechanical junction between the sarcolemma and collagen. Therefore, it is possible that merosin plays a role in force transmission between muscle fibers and collagen. We hypothesized that deficiency in merosin may alter passive muscle stiffness, viscoelastic properties, and contractile muscle force in skeletal muscles. We used the dy/dy mouse, a merosin-deficient mouse model, to examine changes in passive and active muscle mechanics. After mice were anesthetized and the diaphragm or the biceps femoris hindlimb muscle was excised, passive length-tension relationships, stress-relaxation curves, or isometric contractile properties were determined with an in vitro biaxial mechanical testing apparatus. Compared with controls, extensibility was smaller in the muscle fiber direction and the transverse fiber direction of the mutant mice. The relaxed elastic modulus was smaller in merosin-deficient diaphragms compared with controls. Interestingly, maximal muscle tetanic stress was depressed in muscles from the mutant mice during uniaxial loading but not during biaxial loading. However, presence of transverse passive stretch increases maximal contractile stress in both the mutant and normal mice. Our data suggest that merosin contributes to muscle passive stiffness, viscoelasticity, and contractility and that the mechanism by which force is transmitted between adjacent myofibers via merosin possibly in shear.
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Wakeling, James M., Ollie M. Blake, Iris Wong, Manku Rana, and Sabrina S. M. Lee. "Movement mechanics as a determinate of muscle structure, recruitment and coordination." Philosophical Transactions of the Royal Society B: Biological Sciences 366, no. 1570 (May 27, 2011): 1554–64. http://dx.doi.org/10.1098/rstb.2010.0294.
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During muscle contractions, the muscle fascicles may shorten at a rate different from the muscle-tendon unit, and the ratio of these velocities is its gearing. Appropriate gearing allows fascicles to reduce their shortening velocities and allows them to operate at effective shortening velocities across a range of movements. Gearing of the muscle fascicles within the muscle belly is the result of rotations of the fascicles and bulging of the belly. Variable gearing can also occur as a result of tendon length changes that can be caused by changes in the relative timing of muscle activity for different mechanical tasks. Recruitment patterns of slow and fast fibres are crucial for achieving optimal muscle performance, and coordination between muscles is related to whole limb performance. Poor coordination leads to inefficiencies and loss of power, and optimal coordination is required for high power outputs and high mechanical efficiencies from the limb. This paper summarizes key studies in these areas of neuromuscular mechanics and results from studies where we have tested these phenomena on a cycle ergometer are presented to highlight novel insights. The studies show how muscle structure and neural activation interact to generate smooth and effective motion of the body.
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Miyanishi, Shouji, and Tadashi Kashima. "Trajectory Formation in Human Arm Movements Based on Joint Motor Model Demonstrating Muscle Characteristics(Musculo-Skeletal Mechanics)." Proceedings of the Asian Pacific Conference on Biomechanics : emerging science and technology in biomechanics 2004.1 (2004): 149–50. http://dx.doi.org/10.1299/jsmeapbio.2004.1.149.
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Wang, Simon, and Stuart M. McGill. "Links between the Mechanics of Ventilation and Spine Stability." Journal of Applied Biomechanics 24, no. 2 (May 2008): 166–74. http://dx.doi.org/10.1123/jab.24.2.166.
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Spine stability is ensured through isometric coactivation of the torso muscles; however, these same muscles are used cyclically to assist ventilation. Our objective was to investigate this apparent paradoxical role (isometric contraction for stability or rhythmic contraction for ventilation) of some selected torso muscles that are involved in both ventilation and support of the spine. Eight, asymptomatic, male subjects provided data on low back moments, motion, muscle activation, and hand force. These data were input to an anatomically detailed, biologically driven model from which spine load and a lumbar spine stability index was obtained. Results revealed that subjects entrained their torso stabilization muscles to breathe during demanding ventilation tasks. Increases in lung volume and back extensor muscle activation coincided with increases in spine stability, whereas declines in spine stability were observed during periods of low lung inflation volume and simultaneously low levels of torso muscle activation. As a case study, aberrant ventilation motor patterns (poor muscle entrainment), seen in one subject, compromised spine stability. Those interested in rehabilitation of patients with lung compromise and concomitant back troubles would be assisted with knowledge of the mechanical links between ventilation during tasks that impose spine loading.
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Olesen, Annesofie T., Bente R. Jensen, Toni L. Uhlendorf, Randy W. Cohen, Guus C. Baan, and Huub Maas. "Muscle-specific changes in length-force characteristics of the calf muscles in the spastic Han-Wistar rat." Journal of Applied Physiology 117, no. 9 (November 1, 2014): 989–97. http://dx.doi.org/10.1152/japplphysiol.00587.2014.
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The purpose of the present study was to investigate muscle mechanical properties and mechanical interaction between muscles in the lower hindlimb of the spastic mutant rat. Length-force characteristics of gastrocnemius (GA), soleus (SO), and plantaris (PL) were assessed in anesthetized spastic and normally developed Han-Wistar rats. In addition, the extent of epimuscular myofascial force transmission between synergistic GA, SO, and PL, as well as between the calf muscles and antagonistic tibialis anterior (TA), was investigated. Active length-force curves of spastic GA and PL were narrower with a reduced maximal active force. In contrast, active length-force characteristics of spastic SO were similar to those of controls. In reference position (90° ankle and knee angle), higher resistance to ankle dorsiflexion and increased passive stiffness was found for the spastic calf muscle group. At optimum length, passive stiffness and passive force of spastic GA were decreased, whereas those of spastic SO were increased. No mechanical interaction between the calf muscles and TA was found. As GA was lengthened, force from SO and PL declined despite a constant muscle-tendon unit length of SO and PL. However, the extent of this interaction was not different in spastic rats. In conclusion, the effects of spasticity on length-force characteristics were muscle specific. The changes observed for GA and PL muscles are consistent with the changes in limb mechanics reported for human patients. Our results indicate that altered mechanics in spastic rats cannot be attributed to differences in mechanical interaction, but originate from individual muscular structures.
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Wakeling, James M., Katrin Uehli, and Antra I. Rozitis. "Muscle fibre recruitment can respond to the mechanics of the muscle contraction." Journal of The Royal Society Interface 3, no. 9 (February 10, 2006): 533–44. http://dx.doi.org/10.1098/rsif.2006.0113.
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This study investigates the motor unit recruitment patterns between and within muscles of the triceps surae during cycling on a stationary ergometer at a range of pedal speeds and resistances. Muscle activity was measured from the soleus (SOL), medial gastrocnemius (MG) and lateral gastrocnemius (LG) using surface electromyography (EMG) and quantified using wavelet and principal component analysis. Muscle fascicle strain rates were quantified using ultrasonography, and the muscle–tendon unit lengths were calculated from the segmental kinematics. The EMG intensities showed that the body uses the SOL relatively more for the higher-force, lower-velocity contractions than the MG and LG. The EMG spectra showed a shift to higher frequencies at faster muscle fascicle strain rates for MG: these shifts were independent of the level of muscle activity, the locomotor load and the muscle fascicle strain. These results indicated that a selective recruitment of the faster motor units occurred within the MG muscle in response to the increasing muscle fascicle strain rates. This preferential recruitment of the faster fibres for the faster tasks indicates that in some circumstances motor unit recruitment during locomotion can match the contractile properties of the muscle fibres to the mechanical demands of the contraction.
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Nichols, T. Richard. "Distributed force feedback in the spinal cord and the regulation of limb mechanics." Journal of Neurophysiology 119, no. 3 (March 1, 2018): 1186–200. http://dx.doi.org/10.1152/jn.00216.2017.
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This review is an update on the role of force feedback from Golgi tendon organs in the regulation of limb mechanics during voluntary movement. Current ideas about the role of force feedback are based on modular circuits linking idealized systems of agonists, synergists, and antagonistic muscles. In contrast, force feedback is widely distributed across the muscles of a limb and cannot be understood based on these circuit motifs. Similarly, muscle architecture cannot be understood in terms of idealized systems, since muscles cross multiple joints and axes of rotation and further influence remote joints through inertial coupling. It is hypothesized that distributed force feedback better represents the complex mechanical interactions of muscles, including the stresses in the musculoskeletal network born by muscle articulations, myofascial force transmission, and inertial coupling. Together with the strains of muscle fascicles measured by length feedback from muscle spindle receptors, this integrated proprioceptive feedback represents the mechanical state of the musculoskeletal system. Within the spinal cord, force feedback has excitatory and inhibitory components that coexist in various combinations based on motor task and integrated with length feedback at the premotoneuronal and motoneuronal levels. It is concluded that, in agreement with other investigators, autogenic, excitatory force feedback contributes to propulsion and weight support. It is further concluded that coexistent inhibitory force feedback, together with length feedback, functions to manage interjoint coordination and the mechanical properties of the limb in the face of destabilizing inertial forces and positive force feedback, as required by the accelerations and changing directions of both predator and prey.
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De Troyer, André, and Theodore A. Wilson. "Effect of acute inflation on the mechanics of the inspiratory muscles." Journal of Applied Physiology 107, no. 1 (July 2009): 315–23. http://dx.doi.org/10.1152/japplphysiol.91472.2008.
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When the lung is inflated acutely, the capacity of the diaphragm to generate pressure, in particular pleural pressure (Ppl), is impaired because the muscle during contraction is shorter and generates less force. At very high lung volumes, the pressure-generating capacity of the diaphragm may be further reduced by an increase in the muscle radius of curvature. Lung inflation similarly impairs the pressure-generating capacity of the inspiratory intercostal muscles, both the parasternal intercostals and the external intercostals. In contrast to the diaphragm, however, this adverse effect is largely related to the orientation and motion of the ribs, rather than the ability of the muscles to generate force. During combined activation of the two sets of muscles, the change in Ppl is larger than during isolated diaphragm activation, and this added load on the diaphragm reduces the shortening of the muscle and increases muscle force. In addition, activation of the diaphragm suppresses the cranial displacement of the passive diaphragm that occurs during isolated intercostal contraction and increases the respiratory effect of the intercostals. As a result, the change in Ppl generated during combined diaphragm-intercostal activation is greater than the sum of the pressures generated during separate muscle activation. Although this synergistic interaction becomes particularly prominent at high lung volumes, lung inflation, either bilateral or unilateral, places a substantial stress on the inspiratory muscle pump.
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Marcucci, Lorenzo, Tetsuya Shimokawa, Mitsuhiro Iwaki, and Toshio Yanagida. "1P-113 Brownian motor in muscle mechanics(Muscle, The 47th Annual Meeting of the Biophysical Society of Japan)." Seibutsu Butsuri 49, supplement (2009): S81. http://dx.doi.org/10.2142/biophys.49.s81_2.
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Kleinteich, Thomas, Alexander Haas, and Adam P. Summers. "Caecilian jaw-closing mechanics: integrating two muscle systems." Journal of The Royal Society Interface 5, no. 29 (May 15, 2008): 1491–504. http://dx.doi.org/10.1098/rsif.2008.0155.
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Caecilians (Lissamphibia: Gymnophiona) are unique among vertebrates in having two sets of jaw-closing muscles, one on either side of the jaw joint. Using data from high-resolution X-ray radiation computed tomography scans, we modelled the effect of these two muscle groups ( mm. levatores mandibulae and m. interhyoideus posterior ) on bite force over a range of gape angles, employing a simplified lever arm mechanism that takes into account muscle cross-sectional area and fibre angle. Measurements of lever arm lengths, muscle fibre orientations and physiological cross-sectional area of cranial muscles were available from three caecilian species: Ichthyophis cf. kohtaoensis ; Siphonops annulatus ; and Typhlonectes natans . The maximal gape of caecilians is restricted by a critical gape angle above which the mm. levatores mandibulae will open the jaw and destabilize the mandibular joint. The presence of destabilizing forces in the caecilian jaw mechanism may be compensated for by a mandibular joint in that the fossa is wrapped around the condyle to resist dislocation. The caecilian skull is streptostylic; the quadrate–squamosal complex moves with respect to the rest of the skull. This increases the leverage of the jaw-closing muscles. We also demonstrate that the unusual jaw joint requires streptostyly because there is a dorsolateral movement of the quadrate–squamosal complex when the jaw closes. The combination of the two jaw-closing systems results in high bite forces over a wide range of gape angles, an important advantage for generalist feeders such as caecilians. The relative sizes and leverage mechanics of the two closing systems allow one to exert more force when the other has a poor mechanical advantage. This effect is seen in all three species we examined. In the aquatic T. natans , with its less well-roofed skull, there is a larger contribution of the mm. levatores mandibulae to total bite force than in the terrestrial I . cf. kohtaoensis and S. annulatus .
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Roberts, T. J., M. S. Chen, and C. R. Taylor. "Energetics of bipedal running. II. Limb design and running mechanics." Journal of Experimental Biology 201, no. 19 (October 1, 1998): 2753–62. http://dx.doi.org/10.1242/jeb.201.19.2753.
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Compared with quadrupeds, bipedal runners of the same weight have longer legs, take longer steps and can presumably use slower, more economical muscle fibers. One might predict that bipedal running is less expensive, but it is not. We hypothesized that bipeds recruit a larger volume of muscle to support their weight, eliminating the potential economy of longer legs and slower steps. To test our hypothesis, we calculated the relative volume of muscle needed to support body weight over a stride in small dogs (Canis familiaris) and wild turkeys (Meleagris gallopavo) of the same weight. First, we confirmed that turkeys and dogs use approximately the same amount of energy to run at the same speed, and found that turkeys take 1. 8-fold longer steps. Higher muscle forces and/or longer muscle fibers would require a greater volume of active muscle, since muscle volume is proportional to the product of force and fascicle length. We measured both mean fascicle length and mean mechanical advantage for limb extensor muscles. Turkeys generated approximately the same total muscle force to support their weight during running and used muscle fascicles that are on average 2.1 times as long as in dogs, thus requiring a 2.5-fold greater active muscle volume. The greater volume appears to offset the economy of slower rates of force generation, supporting our hypothesis and providing a simple explanation for why it costs the same to run on two and four legs.
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Josephson, Robert. "Comparative Perspectives on Muscle Mechanics." Medicine & Science in Sports & Exercise 39, Supplement (May 2007): 45. http://dx.doi.org/10.1249/01.mss.0000272400.22399.f8.
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Coirault, C., B. Riou, N. Pery-Man, I. Suard, and Y. Lecarpentier. "Mechanics of human quadriceps muscle." Journal of Applied Physiology 77, no. 4 (October 1, 1994): 1769–75. http://dx.doi.org/10.1152/jappl.1994.77.4.1769.
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Mechanics of human quadriceps muscle strips (vastus lateralis; n = 10) were investigated over the whole load continuum. Mechanical experiments were performed at 29 degrees C and in both twitch and tetanus modes. For a given level of isotonic total load (P) and over a large part of the contraction phase, instantaneous velocity (V) was shown to be a unique function of instantaneous length (L), regardless of time and initial length. By considering this time- and initial length-independent mechanical property between instantaneous L and instantaneous V over the whole P continuum, a three-dimensional P-V-L relationship was constructed. Any variations in stimulation conditions modified the time-independent P-V-L diagram. Such modifications in the P-V-L relationship were characteristics of changes in contractile performance. Moreover, characteristics of the P-V relationship were investigated in both twitch and tetanus modes. The curvature of the P-V hyperbola was significantly higher in tetanus at 30 Hz than in twitch mode (P < 0.001). In conclusion, our study indicates that, in human quadriceps muscles, contractility can be defined as the time- and initial length-invariant part of a three-dimensional P-V-L relationship. Moreover, our data are consistent with an increase in economy of force generation in tetanus contractions compared with that in twitches.
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Gagey, O., and E. Hue. "Mechanics of the Deltoid Muscle." Clinical Orthopaedics and Related Research 375 (June 2000): 250–57. http://dx.doi.org/10.1097/00003086-200006000-00030.
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Caiozzo, Vincent J., and Stuart Green. "Breakout Session 1: Muscle Mechanics." Clinical Orthopaedics and Related Research 403 (October 2002): S77—S80. http://dx.doi.org/10.1097/00003086-200210001-00009.
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Hof, A. L. "Muscle mechanics and neuromuscular control." Journal of Biomechanics 36, no. 7 (July 2003): 1031–38. http://dx.doi.org/10.1016/s0021-9290(03)00036-8.
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Barry, D. T., and N. M. Cole. "Fluid mechanics of muscle vibrations." Biophysical Journal 53, no. 6 (June 1988): 899–905. http://dx.doi.org/10.1016/s0006-3495(88)83171-0.
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Rahemi, Hadi, Nilima Nigam, and James M. Wakeling. "The effect of intramuscular fat on skeletal muscle mechanics: implications for the elderly and obese." Journal of The Royal Society Interface 12, no. 109 (August 2015): 20150365. http://dx.doi.org/10.1098/rsif.2015.0365.
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Skeletal muscle accumulates intramuscular fat through age and obesity. Muscle quality, a measure of muscle strength per unit size, decreases in these conditions. It is not clear how fat influences this loss in performance. Changes to structural parameters (e.g. fibre pennation and connective tissue properties) affect the muscle quality. This study investigated the mechanisms that lead to deterioration in muscle performance due to changes in intramuscular fat, pennation and aponeurosis stiffness. A finite-element model of the human gastrocnemius was developed as a fibre-reinforced composite biomaterial containing contractile fibres within the base material. The base-material properties were modified to include intramuscular fat in five different ways. All these models with fat generated lower fibre stress and muscle quality than their lean counterparts. This effect is due to the higher stiffness of the tissue in the fatty models. The fibre deformations influence their interactions with the aponeuroses, and these change with fatty inclusions. Muscles with more compliant aponeuroses generated lower forces. The muscle quality was further reduced for muscles with lower pennation. This study shows that whole-muscle force is dependent on its base-material properties and changes to the base material due to fatty inclusions result in reductions to force and muscle quality.
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Rome, L. C. "Influence of temperature on muscle recruitment and muscle function in vivo." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 259, no. 2 (August 1, 1990): R210—R222. http://dx.doi.org/10.1152/ajpregu.1990.259.2.r210.
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Temperature has a large influence on the maximum velocity of shortening (Vmax) and maximum power output of muscle (Q10 = 1.5-3). In some animals, maximum performance and maximum sustainable performance show large temperature sensitivities, because these parameters are dependent solely on mechanical power output of the muscles. The mechanics of locomotion (sarcomere length excursions and muscle-shortening velocities, V) at a given speed, however, are precisely the same at all temperatures. Animals compensate for the diminished power output of their muscles at low temperatures by compressing their recruitment order into a narrower range of locomotor speeds, that is, recruiting more muscle fibers and faster fiber types at a given speed. By examining V/Vmax, I calculate that fish at 10 degrees C must recruit 1.53-fold greater fiber cross section than at 20 degrees C. V/Vmax also appears to be an important design constraint in muscle. It sets the lowest V and the highest V over which a muscle can be used effectively. Because the Vmax of carp slow red muscle has a Q10 of 1.6 between 10 and 20 degrees C, the slow aerobic fibers can be used over a 1.6-fold greater range of swim speeds at the warmer temperature. In some species of fish, Vmax can be increased during thermal acclimation, enabling animals to swim at higher speeds.
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Robertson, Benjamin D., and Gregory S. Sawicki. "Unconstrained muscle-tendon workloops indicate resonance tuning as a mechanism for elastic limb behavior during terrestrial locomotion." Proceedings of the National Academy of Sciences 112, no. 43 (October 12, 2015): E5891—E5898. http://dx.doi.org/10.1073/pnas.1500702112.
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In terrestrial locomotion, there is a missing link between observed spring-like limb mechanics and the physiological systems driving their emergence. Previous modeling and experimental studies of bouncing gait (e.g., walking, running, hopping) identified muscle-tendon interactions that cycle large amounts of energy in series tendon as a source of elastic limb behavior. The neural, biomechanical, and environmental origins of these tuned mechanics, however, have remained elusive. To examine the dynamic interplay between these factors, we developed an experimental platform comprised of a feedback-controlled servo-motor coupled to a biological muscle-tendon. Our novel motor controller mimicked in vivo inertial/gravitational loading experienced by muscles during terrestrial locomotion, and rhythmic patterns of muscle activation were applied via stimulation of intact nerve. This approach was based on classical workloop studies, but avoided predetermined patterns of muscle strain and activation—constraints not imposed during real-world locomotion. Our unconstrained approach to position control allowed observation of emergent muscle-tendon mechanics resulting from dynamic interaction of neural control, active muscle, and system material/inertial properties. This study demonstrated that, despite the complex nonlinear nature of musculotendon systems, cyclic muscle contractions at the passive natural frequency of the underlying biomechanical system yielded maximal forces and fractions of mechanical work recovered from previously stored elastic energy in series-compliant tissues. By matching movement frequency to the natural frequency of the passive biomechanical system (i.e., resonance tuning), muscle-tendon interactions resulting in spring-like behavior emerged naturally, without closed-loop neural control. This conceptual framework may explain the basis for elastic limb behavior during terrestrial locomotion.
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Gerthoffer, William T. "Actin cytoskeletal dynamics in smooth muscle contraction." Canadian Journal of Physiology and Pharmacology 83, no. 10 (October 1, 2005): 851–56. http://dx.doi.org/10.1139/y05-088.
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Smooth muscles develop isometric force over a very wide range of cell lengths. The molecular mechanisms of this phenomenon are undefined, but are described as reflecting "mechanical plasticity" of smooth muscle cells. Plasticity is defined here as a persistent change in cell structure or function in response to a change in the environment. Important environmental stimuli that trigger muscle plasticity include chemical (e.g., neurotransmitters, autacoids, and cytokines) and external mechanical signals (e.g., applied stress and strain). Both kinds of signals are probably transduced by ionic and protein kinase signaling cascades to alter gene expression patterns and changes in the cytoskeleton and contractile system. Defining the signaling mechanisms and effector proteins mediating phenotypic and mechanical plasticity of smooth muscles is a major goal in muscle cell biology. Some of the signaling cascades likely to be important include calcium-dependent protein kinases, small GTPases (Rho, Rac, cdc42), Rho kinase, protein kinase C (PKC), Src family tyrosine kinases, mitogen-activated protein (MAP) kinases, and p21 activated protein kinases (PAK). There are many potential targets for these signaling cascades including nuclear processes, metabolic pathways, and structural components of the cytoskeleton. There is growing appreciation of the dynamic nature of the actin cytoskeleton in smooth muscles and the necessity for actin remodeling to occur during contraction. The actin cytoskeleton serves many functions that are probably critical for muscle plasticity including generation and transmission of force vectors, determination of cell shape, and assembly of signal transduction machinery. Evidence is presented showing that actin filaments are dynamic and that actin-associated proteins comprising the contractile element and actin attachment sites are necessary for smooth muscle contraction.Key words: integrin, muscle mechanics, paxillin, Rho, HSP27.
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Cheng, C. H., T. Y. Chen, Y. W. Kuo, and J. L. Wang. "The Mechanics of Cervical Muscle Recruitment on Cervical Spine Stability —A Biomechanical in Vitro Study using Porcine Model." Journal of Mechanics 24, no. 1 (March 2008): 63–68. http://dx.doi.org/10.1017/s1727719100001568.
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ABSTRACTCervical muscles are crucial in providing the stability of the cervical spine. Many in vitro studies have investigated the relationship between muscle force and stability directly. However, the effects of different muscle dysfunctions or muscle recruitments on cervical spine stability are not yet clear and therefore, worthy of study. A spine testing apparatus with muscle force replication activated by pneumatic cylinders was developed to find the effect of muscles on spinal stability. Seven porcine cervical spines (C2-T1) were used. Three pairs of cervical muscles, including neck flexors (sternocleidomastoid, SCM) and neck extensors (splenius capitis, SPL; semispinalis capitis, SSC), were simulated. The experimental tests included: 1. no muscle recruitment, 2. full muscle recruitments, 3. SCM dysfunction, 4. SPL dysfunction, and 5. SSC dysfunction. The external pure moment in sagittal plane was applied from 0 Nm to 2 Nm to examine the stability/flexibility of specimens. The spinal stability was evaluated by the neutral zone (NZ), the range of motion (ROM), the reduced NZ (R_NZ), and the reduced ROM (R_ROM). Loading responses of C7-T1 disc were also measured. The results of this study showed: The activation of cervical muscles decreased the NZ and ROM. The degree of decrease among different muscle dysfunctions, however, was not significantly different. The SPL dysfunction induced larger anterior shear force, while the SCM dysfunction exclusively induced extension moment. In conclusion, the muscle forces could stabilize the cervical spine, but significant decrease in spinal stability was not found among dysfunctions of different muscles. The SCM and SPL dysfunction may result in abnormal stress at the C7-T1 disc.
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GAO, YINGXIN, ANTHONY M. WAAS, and ALAN S. WINEMAN. "MECHANICS OF INJURY TO MUSCLE FIBERS." Journal of Mechanics in Medicine and Biology 07, no. 04 (December 2007): 381–94. http://dx.doi.org/10.1142/s021951940700242x.
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An advanced shear lag model is developed to analyze the stress-shielding effect in injured muscle fiber by introducing the activation strain. The model considers three muscle fibers connected by the endomysium with the middle muscle fiber injured. Stress shielding describes the function of the lateral transmission of force in protecting the injured muscle fibers from being further injured by transferring force in the injured muscle fiber to its adjacent muscle fibers. Parameter studies demonstrate that the mechanical and geometrical properties of muscle fibers and the endomysium as well as the degree of injury can affect the stress-shielding effect. In conclusion, the model successfully demonstrates and captures, at least in a qualitative manner, the lateral transmission of force between an injured and a normal muscle fiber.
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Packer, C. S., and N. L. Stephens. "Mechanics of caudal artery relaxation in control and hypertensive rats." Canadian Journal of Physiology and Pharmacology 63, no. 3 (March 1, 1985): 209–13. http://dx.doi.org/10.1139/y85-039.
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Alterations of smooth muscle function can just as easily stem from mechanical alterations in its ability to relax as from alteration in contraction. Since a failure of arterial smooth muscle to relax may contribute to the development of hypertension, we felt it necessary to study the relaxation process in greater depth. The effect of load on the time course of relaxation of rat caudal artery smooth muscle was analyzed either by comparing afterloaded contractions against various loads or by imposing abrupt alterations in load. Unlike mammalian striated muscles in which relaxation was reported sensitive to loading conditions, relaxation in the smooth muscle of the rat caudal artery (n = 17) was found to be largely independent of loading conditions. This type of relaxation has been termed "inactivation-dependent" relaxation; it is typical of muscle tissue in which the calcium sequestering apparatus is poorly developed. Our results suggest that calcium resequestration, or some biochemical process downstream to it, is the rate-limiting step during relaxation in arterial smooth muscle and that this is not qualitatively different for hypertensive arterial smooth muscle. These analytic techniques were used in the study of relaxation of hypertensive vessels. Quantitative analysis of the relaxation curves showed that both isometric and isotonic relaxation time was prolonged in hypertensive arterial smooth muscle. Prolonged isotonic relaxation indicates that hypertensive arteries remain narrowed for prolonged periods compared with normotensive vessels. Such narrowed vessels may be a factor in the increased total peripheral resistance seen in genetic hypertension.
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De Troyer, A., G. A. Farkas, and V. Ninane. "Mechanics of the parasternal intercostals during occluded breaths in dogs." Journal of Applied Physiology 64, no. 4 (April 1, 1988): 1546–53. http://dx.doi.org/10.1152/jappl.1988.64.4.1546.
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The electrical activity and the respiratory changes in length of the third parasternal intercostal muscle were measured during single-breath airway occlusion in 12 anesthetized, spontaneously breathing dogs in the supine posture. During occluded breaths in the intact animal, the parasternal intercostal was electrically active and shortened while pleural pressure fell. In contrast, after section of the third intercostal nerve at the chondrocostal junction and abolition of parasternal electrical activity, the muscle always lengthened. This inspiratory muscle lengthening must be related to the fall in pleural pressure; it was, however, approximately 50% less than the amount of muscle lengthening produced, for the same fall in pleural pressure, by isolated stimulation of the phrenic nerves. These results indicate that 1) the parasternal inspiratory shortening that occurs during occluded breaths in the dog results primarily from the muscle inspiratory contraction per se, and 2) other muscles of the rib cage, however, contribute to this parasternal shortening by acting on the ribs or the sternum. The present studies also demonstrate the important fact that the parasternal inspiratory contraction in the dog is really agonistic in nature.
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Farris, Dominic James, Benjamin D. Robertson, and Gregory S. Sawicki. "Elastic ankle exoskeletons reduce soleus muscle force but not work in human hopping." Journal of Applied Physiology 115, no. 5 (September 1, 2013): 579–85. http://dx.doi.org/10.1152/japplphysiol.00253.2013.
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Inspired by elastic energy storage and return in tendons of human leg muscle-tendon units (MTU), exoskeletons often place a spring in parallel with an MTU to assist the MTU. However, this might perturb the normally efficient MTU mechanics and actually increase active muscle mechanical work. This study tested the effects of elastic parallel assistance on MTU mechanics. Participants hopped with and without spring-loaded ankle exoskeletons that assisted plantar flexion. An inverse dynamics analysis, combined with in vivo ultrasound imaging of soleus fascicles and surface electromyography, was used to determine muscle-tendon mechanics and activations. Whole body net metabolic power was obtained from indirect calorimetry. When hopping with spring-loaded exoskeletons, soleus activation was reduced (30–70%) and so was the magnitude of soleus force (peak force reduced by 30%) and the average rate of soleus force generation (by 50%). Although forces were lower, average positive fascicle power remained unchanged, owing to increased fascicle excursion (+4–5 mm). Net metabolic power was reduced with exoskeleton assistance (19%). These findings highlighted that parallel assistance to a muscle with appreciable series elasticity may have some negative consequences, and that the metabolic cost associated with generating force may be more pronounced than the cost of doing work for these muscles.
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Hu, Xiao, Wendy M. Murray, and Eric J. Perreault. "Muscle short-range stiffness can be used to estimate the endpoint stiffness of the human arm." Journal of Neurophysiology 105, no. 4 (April 2011): 1633–41. http://dx.doi.org/10.1152/jn.00537.2010.
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The mechanical properties of the human arm are regulated to maintain stability across many tasks. The static mechanics of the arm can be characterized by estimates of endpoint stiffness, considered especially relevant for the maintenance of posture. At a fixed posture, endpoint stiffness can be regulated by changes in muscle activation, but which activation-dependent muscle properties contribute to this global measure of limb mechanics remains unclear. We evaluated the role of muscle properties in the regulation of endpoint stiffness by incorporating scalable models of muscle stiffness into a three-dimensional musculoskeletal model of the human arm. Two classes of muscle models were tested: one characterizing short-range stiffness and two estimating stiffness from the slope of the force-length curve. All models were compared with previously collected experimental data describing how endpoint stiffness varies with changes in voluntary force. Importantly, muscle properties were not fit to the experimental data but scaled only by the geometry of individual muscles in the model. We found that force-dependent variations in endpoint stiffness were accurately described by the short-range stiffness of active arm muscles. Over the wide range of evaluated arm postures and voluntary forces, the musculoskeletal model incorporating short-range stiffness accounted for 98 ± 2, 91 ± 4, and 82 ± 12% of the variance in stiffness orientation, shape, and area, respectively, across all simulated subjects. In contrast, estimates based on muscle force-length curves were less accurate in all measures, especially stiffness area. These results suggest that muscle short-range stiffness is a major contributor to endpoint stiffness of the human arm. Furthermore, the developed model provides an important tool for assessing how the nervous system may regulate endpoint stiffness via changes in muscle activation.
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Merlo, A., and S. Cohen. "Mechanics and neuropeptide responses of feline pylorus and gastric muscle in vitro." American Journal of Physiology-Gastrointestinal and Liver Physiology 256, no. 5 (May 1, 1989): G862—G867. http://dx.doi.org/10.1152/ajpgi.1989.256.5.g862.
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Mechanical properties and neuropeptide responses were compared for feline pyloric and gastric muscle under isometric conditions in vitro. Total tension in antral circular muscle (0.699 +/- 0.003 kg/cm2) was less than in corpus circular (1.597 +/- 0.007 kg/cm2) or longitudinal muscle from the lesser and greater curvatures (1.256 +/- 0.009 and 1.253 +/- 0.007 kg/cm2, n greater than or equal to 55, P less than 0.05). The components of tension at optimal length were similar for all gastric muscles (P greater than 0.1). The pylorus maintained less total tension (0.335 +/- 0.003 kg/cm2) and a greater component of resting tension (75.6%) than gastric muscle (P less than 0.01). Substance P, cholecystokinin-8 (CCK-8), and neurotensin varied in potency and efficacy in circular muscle of the antrum, corpus, and inferior portion of the pyloric ring. Longitudinal muscle and the superior portion of pylorus responded poorly if at all to neuropeptides. Substance P- but not CCK-8- or neurotensin-induced contractions of gastric muscle were reduced by tetrodotoxin (TTX) and atropine (P less than 0.05). Substance P-induced pyloric contractions were TTX sensitive (P less than 0.05) but were unaffected by atropine. We concluded that 1) length-tension properties of gastric muscle are similar and distinct from the pylorus and that 2) neuropeptide efficacy varies regionally within the feline stomach and within the pylorus.
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Poppele, RE, and DC Quick. "Effect of intrafusal muscle mechanics on mammalian muscle spindle sensitivity." Journal of Neuroscience 5, no. 7 (July 1, 1985): 1881–85. http://dx.doi.org/10.1523/jneurosci.05-07-01881.1985.
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Merlo, A., and S. Cohen. "Neuropeptide responses and mechanics of the proximal and distal feline colon in vitro." American Journal of Physiology-Gastrointestinal and Liver Physiology 255, no. 6 (December 1, 1988): G787—G793. http://dx.doi.org/10.1152/ajpgi.1988.255.6.g787.
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Mechanical properties and responses to neuropeptides were compared for proximal and distal feline colonic muscle. Proximal longitudinal (PL), proximal circular (PC), distal longitudinal (DL), and distal circular (DC) muscles were studied in vitro under isometric conditions. Total tension in DL [1.636 +/- 0.009 (SE) kg/cm2] was greater than in DC (0.699 +/- 0.004 kg/cm2) or PC (0.710 +/- 0.005 kg/cm2, P less than 0.05). Longitudinal muscle developed proportionately more active tension than circular muscle at each region (80.9% in DL vs. 54.1% in DC and 77.1% in PL vs. 52.3% in PC, P less than 0.01). Neuropeptides varied in potency and efficacy. Cholecystokinin octapeptide (CCK-8) was the most potent and efficacious in PL and substance P was the most efficacious in PC muscle (P less than 0.05). Substance P was more efficacious whereas CCK-8 and neurotensin were less efficacious in PC than PL muscle (P less than 0.01). DL muscle did not respond to CCK-8. DC muscle did not respond to CCK-8 or neurotensin. Isometric contractions to each neuropeptide were insensitive to tetrodotoxin. We conclude that 1) mechanical properties of circular and longitudinal colonic muscle differ and 2) responses to neuropeptides depend on anatomic region and intrinsic properties.
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Ghadiali, Samir N., J. Douglas Swarts, and William J. Doyle. "Effect of Tensor Veli Palatini Muscle Paralysis on Eustachian Tube Mechanics." Annals of Otology, Rhinology & Laryngology 112, no. 8 (August 2003): 704–11. http://dx.doi.org/10.1177/000348940311200810.
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Several physiological functions, such as regulating middle ear (ME) pressure and clearing ME fluid into the nasopharynx, require an opening of the collapsed eustachian tube (ET). The ability to perform these functions has been related to several mechanical properties of the ET: opening pressure (Popen), compliance (ETC), and hysteresis (η). These global properties may be influenced by the mechanics of the surrounding tissue and/or the mucosa-air interface. In this study, we investigated the influence of tissue mechanics by paralyzing the right tensor veli palatini (TVP) muscle in 12 cynomolgus monkeys via botulinum toxin injection. A previously developed modified forced-response protocol was used to measure Popen, ETC, and η under normal conditions and after muscle paralysis. The loss of muscle tone and/or stiffness resulted in a significant decrease in Popen (p < .01) and a significant increase in ETC (p < .01). In addition, muscle paralysis reduced the viscoelastic properties of the TVP muscle and therefore resulted in a significant decrease in η (p < .05). A comparison with previous measurements on the influence of surface tension mechanics indicates that the ET's compliance is primarily determined by tissue elastic properties. The ET hysteresis, however, is equally affected by viscoelastic tissue properties and surface tension hysteretic properties. Knowledge of how these physical components affect the global mechanical environment may lead to improved treatments for ET dysfunction that target the underlying mechanical abnormality.
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Okazawa, M., P. Pare, and J. Road. "Tracheal smooth muscle mechanics in vivo." Journal of Applied Physiology 68, no. 1 (January 1, 1990): 209–19. http://dx.doi.org/10.1152/jappl.1990.68.1.209.
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We applied the technique of sonomicrometry to directly measure length changes of the trachealis muscle in vivo. Pairs of small 1-mm piezoelectric transducers were placed in parallel with the muscle fibers in the posterior tracheal wall in seven anesthetized dogs. Length changes were recorded during mechanical ventilation and during complete pressure-volume curves of the lung. The trachealis muscle showed spontaneous fluctuations in base-line length that disappeared after vagotomy. Before vagotomy passive pressure-length curves showed marked hysteresis and length changed by 18.5 +/- 13.2% (SD) resting length at functional residual capacity (LFRC) from FRC to total lung capacity (TLC) and by 28.2 +/- 16.2% LFRC from FRC to residual volume (RV). After vagotomy hysteresis decreased considerably and length now changed by 10.4 +/- 3.7% LFRC from FRC to TLC and by 32.5 +/- 14.6% LFRC from FRC to RV. Bilateral supramaximal vagal stimulation produced a mean maximal active shortening of 28.8 +/- 14.2% resting length at any lung volume (LR) and shortening decreased at lengths above FRC. The mean maximal velocity of shortening was 4.2 +/- 3.9% LR.S-1. We conclude that sonomicrometry may be used to record smooth muscle length in vivo. Vagal tone strongly influences passive length change. In vivo active shortening and velocity of shortening are less than in vitro, implying that there are significant loads impeding shortening in vivo.
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Bojsen-Møller, Jens. "Muscle Tendon Mechanics Investigated by Ultrasonography." Medicine & Science in Sports & Exercise 40, Supplement (May 2008): 50. http://dx.doi.org/10.1249/01.mss.0000321051.19142.f5.
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Tunik, Bernard D. "Cardiac Muscle Mechanics. Richard A. Meiss." Quarterly Review of Biology 64, no. 2 (June 1989): 248. http://dx.doi.org/10.1086/416349.
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van Eijden, T. M. G. J., and J. H. Koolstra. "A model for mylohyoid muscle mechanics." Journal of Biomechanics 31, no. 11 (November 1998): 1017–24. http://dx.doi.org/10.1016/s0021-9290(98)00111-0.
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de Tombe, Pieter P., and Henk E. D. J. ter Keurs. "Cardiac muscle mechanics: Sarcomere length matters." Journal of Molecular and Cellular Cardiology 91 (February 2016): 148–50. http://dx.doi.org/10.1016/j.yjmcc.2015.12.006.
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Cooper, Donald S. "Leopold réthi and laryngeal muscle mechanics." Journal of Voice 5, no. 4 (January 1991): 354–59. http://dx.doi.org/10.1016/s0892-1997(05)80068-2.
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Johansson, B. "Current problems in smooth muscle mechanics." Experientia 41, no. 8 (August 1985): 1017–20. http://dx.doi.org/10.1007/bf01952124.
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Lieber, Richard L., and Sue C. Bodine-Fowler. "Skeletal Muscle Mechanics: Implications for Rehabilitation." Physical Therapy 73, no. 12 (December 1, 1993): 844–56. http://dx.doi.org/10.1093/ptj/73.12.844.
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Capasso, J. M., P. Li, and P. Anversa. "Myocardial mechanics predict hemodynamic performance during normal function and alcohol-induced dysfunction in rats." American Journal of Physiology-Heart and Circulatory Physiology 261, no. 6 (December 1, 1991): H1880—H1888. http://dx.doi.org/10.1152/ajpheart.1991.261.6.h1880.
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To determine whether mechanical evaluation of muscle tissue removed from the myocardium can be employed as a direct indicator of cardiac contractile performance in situ, isometric and isotonic parameters of muscle mechanics in vitro were correlated with in vivo global functional characteristics of the same heart. Twelve-month-old animals maintained on standard food and water were employed as representative of normal cardiac function. Animals of identical age with left ventricular (LV) dysfunction induced by oral alcohol (30%) ingestion from 4 to 12 mo were utilized to represent depressed cardiac performance. Accordingly, 24 h after the establishment of the hemodynamic profile for a control or experimental heart, the LV posterior papillary muscle was removed from the same heart and examined isometrically and isotonically. Least squares regression analysis was employed to establish a correlation coefficient and P values between various in vitro and in vivo parameters. Hemodynamic measurements were performed under chloral hydrate anesthesia and LV pump performance was evaluated with respect to aortic and ventricular pressures and the rates of rise and decay of the LV pressure trace. Papillary muscles were evaluated with respect to timing parameters of the isometric and isotonic twitch, the first derivative of isometric tension development, and the speed of muscle shortening at increasing physiologic loads. LV peak rate of pressure rise and decay were then correlated with the various isometric and isotonic properties. Myocardial mechanics and hemodynamics revealed depressed function in the papillary muscles and hearts from alcoholic rats. Moreover, significant correlations were found between the LV rate of pressure change (peak +dP/dt and -dP/dt) and both isometric and isotonic twitch measurements.(ABSTRACT TRUNCATED AT 250 WORDS)
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Higham, Timothy E., Andrew A. Biewener, and Scott L. Delp. "Mechanics, modulation and modelling: how muscles actuate and control movement." Philosophical Transactions of the Royal Society B: Biological Sciences 366, no. 1570 (May 27, 2011): 1463–65. http://dx.doi.org/10.1098/rstb.2010.0354.
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Animal movement is often complex, unsteady and variable. The critical role of muscles in animal movement has captivated scientists for over 300 years. Despite this, emerging techniques and ideas are still shaping and advancing the field. For example, sonomicrometry and ultrasound techniques have enhanced our ability to quantify muscle length changes under in vivo conditions. Robotics and musculoskeletal models have benefited from improved computational tools and have enhanced our ability to understand muscle function in relation to movement by allowing one to simulate muscle–tendon dynamics under realistic conditions. The past decade, in particular, has seen a rapid advancement in technology and shifts in paradigms related to muscle function. In addition, there has been an increased focus on muscle function in relation to the complex locomotor behaviours, rather than relatively simple (and steady) behaviours. Thus, this Theme Issue will explore integrative aspects of muscle function in relation to diverse locomotor behaviours such as swimming, jumping, hopping, running, flying, moving over obstacles and transitioning between environments. Studies of walking and running have particular relevance to clinical aspects of human movement and sport. This Theme Issue includes contributions from scientists working on diverse taxa, ranging from humans to insects. In addition to contributions addressing locomotion in various taxa, several manuscripts will focus on recent advances in neuromuscular control and modulation during complex behaviours. Finally, some of the contributions address recent advances in biomechanical modelling and powered prostheses. We hope that our comprehensive and integrative Theme Issue will form the foundation for future work in the fields of neuromuscular mechanics and locomotion.
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Bozler, E. "Mechanics of tonus fibers of frog muscle." American Journal of Physiology-Cell Physiology 253, no. 4 (October 1, 1987): C599—C606. http://dx.doi.org/10.1152/ajpcell.1987.253.4.c599.
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Contractions with two phases of relaxation are induced by brief strong stimulation in some frog muscles. The first phase with rapid relaxation is produced by the twitch fibers; the second phase, which is very slow and is only present after strong stimulation, represents the relaxation of the tonus fibers. At moderate loads, half time of isotonic relaxation of these fibers is as long as 30 min at 2 degrees C, but the rate varies with the load and depends on the condition of the frogs. With regard to the rate of relaxation, the tonus fibers resemble molluscan catch muscles. In tonus fibers, rapid isotonic and isometric relaxation can be induced by a small extension; shortening opposes this effect. These responses are like the length responses previously found in various types of striated muscle. They go in the same direction as the well-known metabolic effects of length changes (Fenn effect). After a large extension by an increase in load there is no active shortening when the load is returned to the previous value. This and other observations show that the slowness of relaxation is not due to sustained activity, but is determined by the strength of the contractile bonds formed during contraction. Because activity during relaxation is very low, it is unlikely that length responses are caused by a modification of the cross-bridge cycle. It is suggested that length changes act through a mechanism that is separate from that initiating contraction, but alters the speed of relaxation by making the cross bridges weaker or stronger.
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Konow, Nicolai, and Thomas J. Roberts. "The series elastic shock absorber: tendon elasticity modulates energy dissipation by muscle during burst deceleration." Proceedings of the Royal Society B: Biological Sciences 282, no. 1804 (April 7, 2015): 20142800. http://dx.doi.org/10.1098/rspb.2014.2800.
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During downhill running, manoeuvring, negotiation of obstacles and landings from a jump, mechanical energy is dissipated via active lengthening of limb muscles. Tendon compliance provides a ‘shock-absorber’ mechanism that rapidly absorbs mechanical energy and releases it more slowly as the recoil of the tendon does work to stretch muscle fascicles. By lowering the rate of muscular energy dissipation, tendon compliance likely reduces the risk of muscle injury that can result from rapid and forceful muscle lengthening. Here, we examine how muscle–tendon mechanics are modulated in response to changes in demand for energy dissipation. We measured lateral gastrocnemius (LG) muscle activity, force and fascicle length, as well as leg joint kinematics and ground-reaction force, as turkeys performed drop-landings from three heights (0.5–1.5 m centre-of-mass elevation). Negative work by the LG muscle–tendon unit during landing increased with drop height, mainly owing to greater muscle recruitment and force as drop height increased. Although muscle strain did not increase with landing height, ankle flexion increased owing to increased tendon strain at higher muscle forces. Measurements of the length–tension relationship of the muscle indicated that the muscle reached peak force at shorter and likely safer operating lengths as drop height increased. Our results indicate that tendon compliance is important to the modulation of energy dissipation by active muscle with changes in demand and may provide a mechanism for rapid adjustment of function during deceleration tasks of unpredictable intensity.
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AN, K. N., R. L. LINSCHEID, and P. W. BRAND. "Correlation of Physiological Cross-Sectional Areas of Muscle and Tendon." Journal of Hand Surgery 16, no. 1 (February 1991): 66–67. http://dx.doi.org/10.1016/0266-7681(91)90130-g.
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Muscle physiological cross-sectional area, as defined and measured by dividing the volume of the muscle by its fibre length, is proportional to the maximum strength of the muscle. It is one of the important parameters when considering muscle mechanics in sports science and, clinically in tendon transfer procedures. This study reports that tendon cross-sectional area correlated well with the physiological cross-sectional area of associated muscles.
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Lecarpentier, Edouard R., Victor A. Claes, Oumar Timbely, Abdelilah Arsalane, Jacques A. Wipff, Jean-Louis M. Hébert, Francine Y. Michel, and Yves C. Lecarpentier. "Mechanics and energetics of myosin molecular motors from nonpregnant human myometrium." Journal of Applied Physiology 111, no. 4 (October 2011): 1096–105. http://dx.doi.org/10.1152/japplphysiol.00414.2011.
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Mechanical properties of spontaneously contracting isolated nonpregnant human myometrium (NPHM) were investigated throughout the whole continuum of load from zero load up to isometry. This made it possible to assess the three-dimensional tension-velocity-length (T-V-L) relationship characterizing the level of contractility and to determine crossbridge (CB) kinetics of myosin molecular motors. Seventy-seven muscle strips were obtained from hysterectomy in 42 nonpregnant patients. Contraction and relaxation parameters were measured during spontaneous mechanical activity. The isotonic tension-peak velocity (T-V) relationship was hyperbolic in 30 cases and nonhyperbolic in 47 cases. When the T-V relationship was hyperbolic, the Huxley formalism could be used to calculate CB kinetics and CB unitary force. At the whole muscle level and for a given isotonic load level, part of the V-L phase plane showed a common pathway, so that a given instantaneous length corresponded to only one possible instantaneous velocity, independent of time and initial length. At the molecular level, rate constants for CB attachment and detachment were dramatically low, ∼100 times lower than those of striated muscles, and ∼5 to 10 times lower than those of other smooth muscles. The CB unitary force was ∼1.4 ± 0.1 pN. NPHM shared similar basic contractile properties with striated muscles, reflected in the three-dimensional T-V-L relationship characterizing the contractile level. Low CB attachment and detachment rate constants made it possible to generate normal CB unitary force and normal muscle tension in NPHM, even though it contracted extremely slowly compared with other muscles.