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Journal articles on the topic 'Muscle activation'
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1
Guadagnin, Eleonora, Davi Mázala, and Yi-Wen Chen. "STAT3 in Skeletal Muscle Function and Disorders." International Journal of Molecular Sciences 19, no. 8 (August 2, 2018): 2265. http://dx.doi.org/10.3390/ijms19082265.
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Signal transducer and activator of transcription 3 (STAT3) signaling plays critical roles in regulating skeletal muscle mass, repair, and diseases. In this review, we discuss the upstream activators of STAT3 in skeletal muscles, with a focus on interleukin 6 (IL6) and transforming growth factor beta 1 (TGF-β1). We will also discuss the double-edged effect of STAT3 activation in the muscles, including the role of STAT3 signaling in muscle hypertrophy induced by exercise training or muscle wasting in cachectic diseases and muscular dystrophies. STAT3 is a critical regulator of satellite cell self-renewal after muscle injury. STAT3 knock out affects satellite cell myogenic progression by impairing proliferation and inducing premature differentiation. Recent studies in STAT3 signaling demonstrated its direct role in controlling myogenic capacity of myoblasts and satellite cells, as well as the potential benefit in using STAT3 inhibitors to treat muscle diseases. However, prolonged STAT3 activation in muscles has been shown to be responsible for muscle wasting by activating protein degradation pathways. It is important to balance the extent of STAT3 activation and the duration and location (cell types) of the STAT3 signaling when developing therapeutic interventions. STAT3 signaling in other tissues and organs that can directly or indirectly affects skeletal muscle health are also discussed.
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Homayounpour, Mohammad, Jonathan D. Mortensen, and Andrew S. Merryweather. "Auditory Warnings Invoking Startle Response Cause Faster and More Intense Neck Muscle Contractions Prior to Head Impacts." Proceedings of the Human Factors and Ergonomics Society Annual Meeting 63, no. 1 (November 2019): 802–6. http://dx.doi.org/10.1177/1071181319631320.
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High-pressure level and sudden sound, especially during an elevated state of alertness can elicit a startle response. Startle response can induce sudden, intense muscle activations. Some studies have shown that increasing neck muscle activation during impact situations can reduce the risk of concussion and neck injury. This research aimed to study muscle coactivation patterns, contraction latency and the level of muscle activation in startle response compared to the voluntary response. To achieve this goal, a testbed capable of applying impacts to the head in four directions was created. Auditory (115 dB) startle stimulus was delivered and muscle activation measured using sEMG on neck muscles during startle and voluntary responses. We investigated a 1000 ms time period starting at the time that the sound is played to the time at impact. Results indicate that the first muscle activation in startle response is 2.1 times higher, 5.9 times faster and involved more muscles than in a voluntary response.
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Hagio, Shota, and Motoki Kouzaki. "The flexible recruitment of muscle synergies depends on the required force-generating capability." Journal of Neurophysiology 112, no. 2 (July 15, 2014): 316–27. http://dx.doi.org/10.1152/jn.00109.2014.
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To simplify redundant motor control, the central nervous system (CNS) may modularly organize and recruit groups of muscles as “muscle synergies.” However, smooth and efficient movements are expected to require not only low-dimensional organization, but also flexibility in the recruitment or combination of synergies, depending on force-generating capability of individual muscles. In this study, we examined how the CNS controls activations of muscle synergies as changing joint angles. Subjects performed multidirectional isometric force generations around right ankle and extracted the muscle synergies using nonnegative matrix factorization across various knee and hip joint angles. As a result, muscle synergies were selectively recruited with merging or decomposition as changing the joint angles. Moreover, the activation profiles, including activation levels and the direction indicating the peak, of muscle synergies across force directions depended on the joint angles. Therefore, we suggested that the CNS selects appropriate muscle synergies and controls their activation patterns based on the force-generating capability of muscles with merging or decomposing descending neural inputs.
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Birdwell, J. Alexander, Levi J. Hargrove, Todd A. Kuiken, and Richard F. ff Weir. "Activation of individual extrinsic thumb muscles and compartments of extrinsic finger muscles." Journal of Neurophysiology 110, no. 6 (September 15, 2013): 1385–92. http://dx.doi.org/10.1152/jn.00748.2012.
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Mechanical and neurological couplings exist between musculotendon units of the human hand and digits. Studies have begun to understand how these muscles interact when accomplishing everyday tasks, but there are still unanswered questions regarding the control limitations of individual muscles. Using intramuscular electromyographic (EMG) electrodes, this study examined subjects' ability to individually initiate and sustain three levels of normalized muscular activity in the index and middle finger muscle compartments of extensor digitorum communis (EDC), flexor digitorum profundus (FDP), and flexor digitorum superficialis (FDS), as well as the extrinsic thumb muscles abductor pollicis longus (APL), extensor pollicis brevis (EPB), extensor pollicis longus (EPL), and flexor pollicis longus (FPL). The index and middle finger compartments each sustained activations with significantly different levels of coactivity from the other finger muscle compartments. The middle finger compartment of EDC was the exception. Only two extrinsic thumb muscles, EPL and FPL, were capable of sustaining individual activations from the other thumb muscles, at all tested activity levels. Activation of APL was achieved at 20 and 30% MVC activity levels with significantly different levels of coactivity. Activation of EPB elicited coactivity levels from EPL and APL that were not significantly different. These results suggest that most finger muscle compartments receive unique motor commands, but of the four thumb muscles, only EPL and FPL were capable of individually activating. This work is encouraging for the neural control of prosthetic limbs because these muscles and compartments may potentially serve as additional user inputs to command prostheses.
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Lee, Sang Wook, Dan Qiu, Heidi C. Fischer, Megan O. Conrad, and Derek G. Kamper. "Modulation of finger muscle activation patterns across postures is coordinated across all muscle groups." Journal of Neurophysiology 124, no. 2 (August 1, 2020): 330–41. http://dx.doi.org/10.1152/jn.00088.2020.
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We examined how hand muscles adapt to changing external (force direction) and internal (posture) conditions. Muscle activations, particularly of the extrinsic extensors, were significantly affected by postural changes of the interphalangeal, but not metacarpophalangeal, joints. Joint impedance was modulated so that the effects of the signal-dependent motor noise on the force output were reduced. Comparisons with theoretical solutions showed that the chosen activation patterns occupied a small portion of the possible solution space, minimizing the maximum activation of any one muscle.
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Knarr, Brian A., Darcy S. Reisman, Stuart A. Binder-Macleod, and Jill S. Higginson. "Changes in Predicted Muscle Coordination with Subject-Specific Muscle Parameters for Individuals after Stroke." Stroke Research and Treatment 2014 (2014): 1–7. http://dx.doi.org/10.1155/2014/321747.
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Muscle weakness is commonly seen in individuals after stroke, characterized by lower forces during a maximal volitional contraction. Accurate quantification of muscle weakness is paramount when evaluating individual performance and response to after stroke rehabilitation. The objective of this study was to examine the effect of subject-specific muscle force and activation deficits on predicted muscle coordination when using musculoskeletal models for individuals after stroke. Maximum force generating ability and central activation ratio of the paretic plantar flexors, dorsiflexors, and quadriceps muscle groups were obtained using burst superimposition for four individuals after stroke with a range of walking speeds. Two models were created per subject: one with generic and one with subject-specific activation and maximum isometric force parameters. The inclusion of subject-specific muscle data resulted in changes in the model-predicted muscle forces and activations which agree with previously reported compensation patterns and match more closely the timing of electromyography for the plantar flexor and hamstring muscles. This was the first study to create musculoskeletal simulations of individuals after stroke with subject-specific muscle force and activation data. The results of this study suggest that subject-specific muscle force and activation data enhance the ability of musculoskeletal simulations to accurately predict muscle coordination in individuals after stroke.
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Spudić, Darjan, Darjan Smajla, Michael David Burnard, and Nejc Šarabon. "Muscle Activation Sequence in Flywheel Squats." International Journal of Environmental Research and Public Health 18, no. 6 (March 19, 2021): 3168. http://dx.doi.org/10.3390/ijerph18063168.
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Background: Muscle coordination is important for rational and effective planning of therapeutic and exercise interventions using equipment that mimics functional movements. Our study was the first to assess muscle coordination during flywheel (FW) squats. Methods: Time-of-peak electromyographic activation order was assessed separately for 8, 4, and 3 leg muscles under four FW loads. A sequential rank agreement permutations tests (SRA) were conducted to assess activation order and Kendall’s tau was used to assess the concordance of activation order across subjects, loads and expected order of activation. Results: SRA revealed a latent muscle activation order at loads 0.05, 0.075, and 0.1, but not at 0.025 kg·m2. Kendall’s tau showed moderate-to-strong concordance between the expected (proximal-to-distal) and the observed muscle activation order only at a load 0.025 kg·m2, regardless of the number of muscles analyzed. Muscle activation order was highly concordant between loads 0.05, 0.075, and 0.1 kg·m2. Conclusions: The results show a specific role of each muscle during the FW squat that is load-dependent. While the lowest load follows the proximal-to-distal principle of muscle activation, higher loads lead to a reorganization of the underlying muscle coordination mechanisms. They require a specific and stable muscle coordination pattern that is not proximal-to-distal.
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Liu, Yali, Ligang Qiang, Qiuzhi Song, Mingsheng Zhao, and Xinyu Guan. "Effects of Backpack Loads on Leg Muscle Activation during Slope Walking." Applied Sciences 10, no. 14 (July 16, 2020): 4890. http://dx.doi.org/10.3390/app10144890.
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Hikers and soldiers usually walk up and down slopes with a load carriage, causing injuries of the musculoskeletal system, especially during a prolonged load journey. The slope walking has been reported to lead to higher leg extensor muscle activities and joint moments. However, most of the studies investigated muscle activities or joint moments during slope walking without load carriage or only investigated the joint moment changes and muscle activities with load carriages during level walking. Whether the muscle activation such as the signal amplitude is influenced by the mixed factor of loads and grades and whether the influence of the degrees of loads and grades on different muscles are equal have not yet been investigated. To explore the effects of backpack loads on leg muscle activation during slope walking, ten young male participants walked at 1.11 m/s on a treadmill with different backpack loads (load masses: 0, 10, 20, and 30 kg) during slope walking (grade: 0, 3, 5, and 10°). Leg muscles, including the gluteus maximus (GM), rectus femoris (RF), hamstrings (HA), anterior tibialis (AT), and medial gastrocnemius (GA), were recorded during walking. The hip, knee, and ankle extensor muscle activations increased during the slope walking, and the hip muscles increased most among hip, knee, and ankle muscles (GM and HA increased by 46% to 207% and 110% to 226%, respectively, during walking steeper than 10° across all load masses (GM: p = 1.32 × 10−8 and HA: p = 2.33 × 10−16)). Muscle activation increased pronouncedly with loads, and the knee extensor muscles increased greater than the hip and ankle muscles (RF increased by 104% to 172% with a load mass greater than 30 kg across all grades (RF: p = 8.86 × 10−7)). The results in our study imply that the hip and knee muscles play an important role during slope walking with loads. The hip and knee extension movements during slope walking should be considerably assisted to lower the muscle activations, which will be useful for designing assistant devices, such as exoskeleton robots, to enhance hikers’ and soldiers’ walking abilities.
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Oliver, Gretchen D., Audrey Stone, and Jessica Washington. "Hamstring and Gluteal Muscle Activation During the Assessment of Dynamic Movements." International Journal of Athletic Therapy and Training 21, no. 4 (July 2016): 30–33. http://dx.doi.org/10.1123/ijatt.2015-0050.
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Recently, sports medicine professionals have shown interest in using dynamic movement assessments to help identify biomechanical risk factors for musculoskeletal injury. Thus the purpose of this study was to propose two movements (single leg step down and single leg lateral hop) that could predict injury and determine if these proposed movements elicited muscle activation of the hamstrings and gluteals. Surface electromyography was employed and muscle activations of the hamstrings and gluteus medius muscles were classified as strong during both the single leg step down (SLSD) and single leg lateral hop (SLLH). Both the hamstrings and gluteus medius muscles are associated with musculoskeletal injury. The SLSD and SLLH cause significantly high muscle activation of both these muscle groups and should be considered for use in dynamic movement assessments.
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Borzelli, Daniele, Stefano Pastorelli, Andrea d’Avella, and Laura Gastaldi. "Virtual Stiffness: A Novel Biomechanical Approach to Estimate Limb Stiffness of a Multi-Muscle and Multi-Joint System." Sensors 23, no. 2 (January 6, 2023): 673. http://dx.doi.org/10.3390/s23020673.
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In recent years, different groups have developed algorithms to control the stiffness of a robotic device through the electromyographic activity collected from a human operator. However, the approaches proposed so far require an initial calibration, have a complex subject-specific muscle model, or consider the activity of only a few pairs of antagonist muscles. This study described and tested an approach based on a biomechanical model to estimate the limb stiffness of a multi-joint, multi-muscle system from muscle activations. The “virtual stiffness” method approximates the generated stiffness as the stiffness due to the component of the muscle-activation vector that does not generate any endpoint force. Such a component is calculated by projecting the vector of muscle activations, estimated from the electromyographic signals, onto the null space of the linear mapping of muscle activations onto the endpoint force. The proposed method was tested by using an upper-limb model made of two joints and six Hill-type muscles and data collected during an isometric force-generation task performed with the upper limb. The null-space projection of the muscle-activation vector approximated the major axis of the stiffness ellipse or ellipsoid. The model provides a good approximation of the voluntary stiffening performed by participants that could be directly implemented in wearable myoelectric controlled devices that estimate, in real-time, the endpoint forces, or endpoint movement, from the mapping between muscle activation and force, without any additional calibrations.
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Arnold, Edith M., and Scott L. Delp. "Fibre operating lengths of human lower limb muscles during walking." Philosophical Transactions of the Royal Society B: Biological Sciences 366, no. 1570 (May 27, 2011): 1530–39. http://dx.doi.org/10.1098/rstb.2010.0345.
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Muscles actuate movement by generating forces. The forces generated by muscles are highly dependent on their fibre lengths, yet it is difficult to measure the lengths over which muscle fibres operate during movement. We combined experimental measurements of joint angles and muscle activation patterns during walking with a musculoskeletal model that captures the relationships between muscle fibre lengths, joint angles and muscle activations for muscles of the lower limb. We used this musculoskeletal model to produce a simulation of muscle–tendon dynamics during walking and calculated fibre operating lengths (i.e. the length of muscle fibres relative to their optimal fibre length) for 17 lower limb muscles. Our results indicate that when musculotendon compliance is low, the muscle fibre operating length is determined predominantly by the joint angles and muscle moment arms. If musculotendon compliance is high, muscle fibre operating length is more dependent on activation level and force–length–velocity effects. We found that muscles operate on multiple limbs of the force–length curve (i.e. ascending, plateau and descending limbs) during the gait cycle, but are active within a smaller portion of their total operating range.
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Marchetti, Paulo Henrique, Josinaldo Jarbas da Silva, Brad Jon Schoenfeld, Priscyla Silva Monteiro Nardi, Silvio Luis Pecoraro, Julia Maria D’Andréa Greve, and Erin Hartigan. "Muscle Activation Differs between Three Different Knee Joint-Angle Positions during a Maximal Isometric Back Squat Exercise." Journal of Sports Medicine 2016 (2016): 1–6. http://dx.doi.org/10.1155/2016/3846123.
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The purpose of this study was to compare muscle activation of the lower limb muscles when performing a maximal isometric back squat exercise over three different positions. Fifteen young, healthy, resistance-trained men performed an isometric back squat at three knee joint angles (20°, 90°, and 140°) in a randomized, counterbalanced fashion. Surface electromyography was used to measure muscle activation of the vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF), biceps femoris (BF), semitendinosus (ST), and gluteus maximus (GM). In general, muscle activity was the highest at 90° for the three quadriceps muscles, yet differences in muscle activation between knee angles were muscle specific. Activity of the GM was significantly greater at 20° and 90° compared to 140°. The BF and ST displayed similar activation at all joint angles. In conclusion, knee position alters muscles activation of the quadriceps and gluteus maximus muscles. An isometric back squat at 90° generates the highest overall muscle activation, yet an isometric back squat at 140° generates the lowest overall muscle activation of the VL and GM only.
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Ross, Stephanie A., and James M. Wakeling. "Muscle shortening velocity depends on tissue inertia and level of activation during submaximal contractions." Biology Letters 12, no. 6 (June 2016): 20151041. http://dx.doi.org/10.1098/rsbl.2015.1041.
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In order to perform external work, muscles must do additional internal work to deform their tissue, and in particular, to overcome the inertia due to their internal mass. However, the contribution of the internal mass within a muscle to the mechanical output of that muscle has only rarely been studied. Here, we use a dynamic, multi-element Hill-type muscle model to examine the effects of the inertial mass within muscle on its contractile performance. We find that the maximum strain-rate of muscle is slower for lower activations and larger muscle sizes. As muscle size increases, the ability of the muscle to overcome its inertial load will decrease, as muscle tension is proportional to cross-sectional area and inertial load is proportional to mass. Thus, muscles that are larger in size will have a higher inertial cost to contraction. Similarly, when muscle size and inertial load are held constant, decreasing muscle activation will increase inertial cost to contraction by reducing muscle tension. These results show that inertial loads within muscle contribute to a slowing of muscle contractile velocities (strain-rates), particularly at the submaximal activations that are typical during animal locomotion.
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Lavender, Steve, Jordan Trafimow, Gunnar B. J. Andersson, R. Samuel Mayer, and Ing-Ho Chen. "Trunk Muscle Activation." Spine 19, no. 7 (April 1994): 771–78. http://dx.doi.org/10.1097/00007632-199404000-00008.
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Warnock, Ben, Danielle L. Gyemi, Evan Brydges, Jennifer M. Stefanczyk, Charles Kahelin, Timothy A. Burkhart, and David M. Andrews. "Comparison of Upper Extremity Muscle Activation Levels Between Isometric and Dynamic Maximum Voluntary Contraction Protocols." International Journal of Kinesiology and Sports Science 7, no. 2 (April 30, 2019): 21. http://dx.doi.org/10.7575/aiac.ijkss.v.7n.2p.21.
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Background: Muscle activations (MA) during maximum voluntary contractions (MVC) are commonly utilized to normalize muscle contributions. Isometric MVC protocols may not activate muscles to the same extent as during dynamic activities, such as falls on outstretched hands (FOOSH), that can occur during sport or recreational activities. Objective: The purpose of this study was to compare the peak MA of upper extremity muscles during isometric and dynamic MVC protocols. Methods: Twenty-four (12 M, 12 F) university-aged participants executed wrist and elbow flexion and extension actions during five-second MVC protocols targeting six upper extremity muscles (three flexors and three extensors). Each protocol [isometric (ISO); dynamic (eccentric (ECC), concentric (CON), elastic band (ELAS), un-resisted (UNRES)] consisted of three contractions (with one-minute rest periods between) during two sessions separated by one week. Muscle activation levels were collected using standard electromyography (EMG) preparations, electrode placements and equipment reported previously. Results: Overall, the ECC and CON dynamic protocols consistently elicited higher peak muscle activation levels than the ISO protocol for both males and females during both sessions. Over 95% of the CON trials resulted in mean and peak muscle activation ratios greater than ISO, with 56.3% being significantly greater than ISO (p < 0.05). Conclusion: Higher activation levels can be elicited in upper extremity muscles when resistance is applied dynamically through a full range of motion during MVC protocols.
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Karahan, Menekşe, and Bülent Sabri Cığalı. "Assessment of hip muscles by surface EMG in gait analysis." Anatomy 14, no. 2 (August 31, 2020): 86–90. http://dx.doi.org/10.2399/ana.20.039.
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Objectives: The rectus femoris muscle flexes the thigh, while the gluteus maximus muscle extends it. Understanding the activations of these two muscles that function in opposition to each other during walking facilitates the interpretation of gait pathologies. The aim of this study was to evaluate the activations of these muscles during walking by using the surface electromyography (EMG) technique. Methods: Twenty female volunteers aged 18–26 years participated in our study. The electrical activation of the rectus femoris and gluteus maximus muscles of the participants was simultaneously evaluated by gait analysis. At the same time, spatiotemporal parameters and phase parameters were obtained. Results: The activation pattern of both muscles was found to be similar. Both muscles reached the highest activation in the swing phase. The lowest activation was also seen in the pre-swing phase. Both muscles were observed to be active in the loading and single-limb support phases. Conclusion: The fact that these two antagonists muscles are active at the same time suggests that one is functioning concentrically, while the other eccentrically. Thus, stabilization of hip joint is provided when the body moves forward.
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Suter, Esther, Walter Herzog, and Robert Bray. "Quadriceps Activation during Knee Extension Exercises in Patients with ACL Pathologies." Journal of Applied Biomechanics 17, no. 2 (May 2001): 87–102. http://dx.doi.org/10.1123/jab.17.2.87.
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This study assessed muscle inhibition in patients with chronic anterior cruciate ligament (ACL) deficiency or ACL reconstruction. A series of protocols were tested for their effectiveness in increasing activity of the individual knee extensor muscles and decreasing muscle inhibition of the whole quadriceps group. Quadriceps muscle inhibition was measured by superimposing an electrical twitch onto the quadriceps muscle during a maximal voluntary knee extension. The level of activation of the individual knee extensor and knee flexor muscles was assessed via electromyography (EMG). Patients with ACL pathologies showed strength deficits and muscle inhibition in the knee extensors of the involved leg and the contralateral leg. Muscle inhibition was statistically significantly greater in ACL-deficient patients compared to ACL-reconstructed patients. When a knee extension was performed in combination with a hip extension, there was a significant increase,p< 0.05, in activation of the vastus medialis and vastus lateralis muscles compared to isolated knee extension. The use of an anti-shear device, designed to help stabilize the ACL-deficient knee, resulted in increased inhibition in the quadriceps muscle. Furthermore, a relatively more complete activation of the vasti compared to the rectus femoris was achieved during a fatiguing isometric contraction. Based on the results of this study, it is concluded that performing knee extension in combination with hip extension, or performing fatiguing knee extensor contractions, may be more effective in fully activating the vasti muscles than an isolated knee extensor contraction. Training interventions are needed to establish whether these exercise protocols are more effective than traditional rehabilitation approaches in decreasing muscle inhibition and achieving better functional recovery, including equal muscle strength in the injured and the contralateral leg.
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SZENT-GYORGYI, A. G. "Muscle Contraction: Calcium in Muscle Activation." Science 238, no. 4824 (October 9, 1987): 223. http://dx.doi.org/10.1126/science.238.4824.223.
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Daly, Janis J., Kristen Roenigk, Roger Cheng, and Robert L. Ruff. "Abnormal Leg Muscle Latencies and Relationship to Dyscoordination and Walking Disability after Stroke." Rehabilitation Research and Practice 2011 (2011): 1–8. http://dx.doi.org/10.1155/2011/313980.
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The purpose was to determine timing characteristics of leg muscle latencies for patients following stroke (>12 months) who had persistent coordination and gait deficits, and to determine the relationships among abnormal latencies, dyscoordination, and gait deficits. We compared nine healthy controls and 27 stroke survivors. Surface electromyography measured activation and deactivation latencies of knee flexor and extensor muscles during a ballistic knee flexion task, consistency of latencies across repetitions, and close coupling between agonist and antagonist muscle latencies. We measured Fugl-Meyer (FM) coordination and the functional gait measure, six minute walk test (6MWT). For stroke subjects, there were significant delays of muscle activation and deactivation, abnormal inconsistency, and abnormal decoupled agonist and antagonist activations. There was good correlation between activation latencies and FM and 6MWT. Results suggest abnormal timing characteristics underlie coordination impairment and dysfunctional gait. These abnormal muscle activation and deactivation timing characteristics are important targets for rehabilitation.
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MacIntosh, Brian R., and M. Reza S. Shahi. "A peripheral governor regulates muscle contraction." Applied Physiology, Nutrition, and Metabolism 36, no. 1 (January 2011): 1–11. http://dx.doi.org/10.1139/h10-073.
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Active skeletal muscles are capable of keeping the global [adenosine triphosphate (ATP)] reasonably constant during exercise, whether it is mild exercise, activating a few motor units, or all-out exercise using a substantial mass of muscle. This could only be accomplished if there were regulatory processes in place not only to replenish ATP as quickly as possible, but also to modulate the rate of ATP use when that rate threatens to exceed the rate of ATP replenishment, a situation that could lead to metabolic catastrophe. This paper proposes that there is a regulatory process or “peripheral governor” that can modulate activation of muscle to avoid metabolic catastrophe. A peripheral governor, working at the cellular level, should be able to reduce the cellular rate of ATP hydrolysis associated with muscle contraction by attenuating activation. This would necessarily cause something we call peripheral fatigue (i.e., reduced contractile response to a given stimulation). There is no doubt that peripheral fatigue occurs. It has been demonstrated in isolated muscles, in muscles in situ with no central nervous system input, and in intact human subjects performing voluntary exercise with small muscle groups or doing whole-body exercise. The regulation of muscle activation is achieved in at least 3 ways (decreasing membrane excitability, inhibiting Ca2+release through ryanodine receptors, and decreasing the availability of Ca2+in the sarcoplasmic reticulum), making this a highly redundant control system. The peripheral governor attenuates cellular activation to reduce the metabolic demand, thereby preserving ATP and the integrity of the cell.
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Ha, Sung-Min, Oh-Yun Kwon, Heon-Seock Cynn, Won-Hwee Lee, Su-Jung Kim, and Kyue-Nam Park. "Selective Activation of the Infraspinatus Muscle." Journal of Athletic Training 48, no. 3 (May 1, 2013): 346–52. http://dx.doi.org/10.4085/1062-6050-48.2.18.
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Context: To improve selective infraspinatus muscle strength and endurance, researchers have recommended selective shoulder external-rotation exercise during rehabilitation or athletic conditioning programs. Although selective strengthening of the infraspinatus muscle is recommended for therapy and training, limited information is available to help clinicians design a selective strengthening program. Objective: To determine the most effective of 4 shoulder external-rotation exercises for selectively stimulating infraspinatus muscle activity while minimizing the use of the middle trapezius and posterior deltoid muscles. Design: Cross-sectional study. Setting: University research laboratory. Patients or Other Participants: A total of 30 healthy participants (24 men, 6 women; age = 22.6 ± 1.7 years, height = 176.2 ± 4.5 cm, mass = 65.6 ± 7.4 kg) from a university population. Intervention(s): The participants were instructed to perform 4 exercises: (1) prone horizontal abduction with external rotation (PER), (2) side-lying wiper exercise (SWE), (3) side-lying external rotation (SER), and (4) standing external-rotation exercise (STER). Main Outcome Measure(s): Surface electromyography signals were recorded from the infraspinatus, middle trapezius, and posterior deltoid muscles. Differences among the exercise positions were tested using a 1-way repeated-measures analysis of variance with Bonferroni adjustment. Results: The infraspinatus muscle activity was greater in the SWE (55.98% ± 18.79%) than in the PER (46.14% ± 15.65%), SER (43.38% ± 22.26%), and STER (26.11% ± 15.00%) (F3,87 = 19.97, P < .001). Furthermore, the SWE elicited the least amount of activity in the middle trapezius muscle (F3,87 = 20.15, P < .001). Posterior deltoid muscle activity was similar in the SWE and SER but less than that measured in the PER and STER (F3,87 = 25.10, P < .001). Conclusions: The SWE was superior to the PER, SER, and STER in maximizing infraspinatus activity with the least amount of middle trapezius and posterior deltoid activity. These findings may help clinicians design effective exercise programs.
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Torres-Oviedo, Gelsy, and Lena H. Ting. "Muscle Synergies Characterizing Human Postural Responses." Journal of Neurophysiology 98, no. 4 (October 2007): 2144–56. http://dx.doi.org/10.1152/jn.01360.2006.
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Postural control is a natural behavior that requires the spatial and temporal coordination of multiple muscles. Complex muscle activation patterns characterizing postural responses suggest the need for independent muscle control. However, our previous work shows that postural responses in cats can be robustly reproduced by the activation of a few muscle synergies. We now investigate whether a similar neural strategy is used for human postural control. We hypothesized that a few muscle synergies could account for the intertrial variability in automatic postural responses from different perturbation directions, as well as different postural strategies. Postural responses to multidirectional support-surface translations in 16 muscles of the lower back and leg were analyzed in nine healthy subjects. Six or fewer muscle synergies were required to reproduce the postural responses of each subject. The composition and temporal activation of several muscle synergies identified across all subjects were consistent with the previously identified “ankle” and “hip” strategies in human postural responses. Moreover, intertrial variability in muscle activation patterns was successfully reproduced by modulating the activity of the various muscle synergies. This suggests that trial-to-trial variations in the activation of individual muscles are correlated and, moreover, represent variations in the amplitude of descending neural commands that activate individual muscle synergies. Finally, composition and temporal activation of most of the muscle synergies were similar across subjects. These results suggest that muscle synergies represent a general neural strategy underlying muscle coordination in postural tasks.
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Ferey, Jeremie L. A., Jeffrey J. Brault, Cheryl A. S. Smith, and Carol A. Witczak. "Constitutive activation of CaMKKα signaling is sufficient but not necessary for mTORC1 activation and growth in mouse skeletal muscle." American Journal of Physiology-Endocrinology and Metabolism 307, no. 8 (October 15, 2014): E686—E694. http://dx.doi.org/10.1152/ajpendo.00322.2014.
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Skeletal muscle loading/overload stimulates the Ca2+-activated, serine/threonine kinase Ca2+/calmodulin-dependent protein kinase kinase-α (CaMKKα); yet to date, no studies have examined whether CaMKKα regulates muscle growth. The purpose of this study was to determine if constitutive activation of CaMKKα signaling could stimulate muscle growth and if so whether CaMKKα is essential for this process. CaMKKα signaling was selectively activated in mouse muscle via expression of a constitutively active form of CaMKKα using in vivo electroporation. After 2 wk, constitutively active CaMKKα expression increased muscle weight (∼10%) and protein content (∼10%), demonstrating that activation of CaMKKα signaling can stimulate muscle growth. To determine if active CaMKKα expression stimulated muscle growth via increased mammalian target of rapamycin complex 1 (mTORC1) signaling and protein synthesis, [3H]phenylalanine incorporation into proteins was assessed with or without the mTORC1 inhibitor rapamycin. Constitutively active CaMKKα increased protein synthesis ∼60%, and this increase was prevented by rapamycin, demonstrating a critical role for mTORC1 in this process. To determine if CaMKKα is essential for growth, muscles from CaMKKα knockout mice were stimulated to hypertrophy via unilateral ablation of synergist muscles (overload). Surprisingly, compared with wild-type mice, muscles from CaMKKα knockout mice exhibited greater growth (∼15%) and phosphorylation of the mTORC1 substrate 70-kDa ribosomal protein S6 kinase (Thr389; ∼50%), demonstrating that CaMKKα is not essential for overload-induced mTORC1 activation or muscle growth. Collectively, these results demonstrate that activation of CaMKKα signaling is sufficient but not necessary for activation of mTORC1 signaling and growth in mouse skeletal muscle.
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McKenzie, Alec, Zachary Crowley-McHattan, Rudi Meir, John Whitting, and Wynand Volschenk. "Fatigue Increases Muscle Activations but Does Not Change Maximal Joint Angles during the Bar Dip." International Journal of Environmental Research and Public Health 19, no. 21 (November 3, 2022): 14390. http://dx.doi.org/10.3390/ijerph192114390.
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The purpose of this study was to profile and compare the bar dip’s kinematics and muscle activation patterns in non-fatigued and fatigued conditions. Fifteen healthy males completed one set of bar dips to exhaustion. Upper limb and trunk kinematics, using 3D motion capture, and muscle activation intensities of nine muscles, using surface electromyography, were recorded. The average kinematics and muscle activations of repetitions 2–4 were considered the non-fatigued condition, and the average of the final three repetitions was considered the fatigued condition. Paired t-tests were used to compare kinematics and muscle activation between conditions. Fatigue caused a significant increase in repetition duration (p < 0.001) and shifted the bottom position to a significantly earlier percentage of the repetition (p < 0.001). There were no significant changes in the peak joint angles measured. However, there were significant changes in body position at the top of the movement. Fatigue also caused an increase in peak activation amplitude in two agonist muscles (pectoralis major [p < 0.001], triceps brachii [p < 0.001]), and three stabilizer muscles. For practitioners prescribing the bar dip, fatigue did not cause drastic alterations in movement technique and appears to target pectoralis major and triceps brachii effectively.
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Hansen, J., G. D. Thomas, T. N. Jacobsen, and R. G. Victor. "Muscle metaboreflex triggers parallel sympathetic activation in exercising and resting human skeletal muscle." American Journal of Physiology-Heart and Circulatory Physiology 266, no. 6 (June 1, 1994): H2508—H2514. http://dx.doi.org/10.1152/ajpheart.1994.266.6.h2508.
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Activation of a metabolically generated reflex in exercising skeletal muscle (muscle metaboreflex) in humans is known to trigger increases in sympathetic nerve activity (SNA) to resting skeletal muscles. In seven healthy human subjects, to determine whether this reflex mechanism also increases SNA to the exercising muscles, we recorded muscle SNA with microelectrodes in the right peroneal nerve and in fascicles of the left peroneal nerve selectively innervating the exercising muscles of the left foot. Subjects performed static toe extension at 20% maximal voluntary contraction alone or in combination with foot ischemia. Only static toe extension at 20% MVC during ischemia activated the muscle metaboreflex. This paradigm caused increases in SNA to exercising muscle that paralleled those to the resting muscles: during the first minute of exercise SNA was unchanged, but during the second minute SNA increased from 29 +/- 2 to 38 +/- 2 bursts/min (P < 0.05) to the exercising muscles and from 30 +/- 3 to 40 +/- 2 bursts/min (P < 0.05) to the resting muscles. These bilateral increases in SNA were maintained when metaboreflex activation was sustained by postexercise foot ischemia. In conclusion, these data provide neurophysiological evidence that the muscle metaboreflex evokes parallel sympathetic activation in exercising and resting human skeletal muscle.
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Li, Wei, Zhongli Li, Shuyan Qie, Huaqing Yang, Xuemei Chen, Yancheng Liu, Zongju Li, and Kuan Zhang. "Analysis of the activation modalities of the lower limb muscles during walking." Technology and Health Care 28, no. 5 (September 18, 2020): 521–32. http://dx.doi.org/10.3233/thc-191939.
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BACKGROUND: Walking is a basic human activity and many orthopedic diseases can manifest with gait abnormalities. However, the muscle activation intervals of lower limbs are not clear. OBJECTIVE: The aim of this study was to explore the contraction patterns of lower limb muscles by analyzing activation intervals using surface electromyography (SEMG) during walking. METHODS: Four muscles including the tibialis anterior (TA), lateral gastrocnemius (LG), medial gastrocnemius (MG), and rectus femoris (RF) of bilateral lower extremity of 92 healthy subjects were selected for SEMG measurements. The number of activations (activation intervals) and the point of the highest root mean square (RMS) EMG signal in the percentage of the gait cycle (GC) were used to analyze muscle activities. RESULTS: The majority of TA and RF showed two activation intervals and both gastrocnemius parts three activation intervals during walking. The point of the highest RMS EMG signal in the percentage of the GC for TA, LG, MG and RF are 5%, 41%, 40%, and 8%, respectively. The activation intervals were mostly affected by age, height, different genders and bilateral limbs. CONCLUSION: This study identified the different activation intervals (four for each muscle) and the proportion of healthy adults in which they occurred during the normal gait cycle. These different activation intervals provided a new insight to evaluate the function of nerves and muscles. In addition, the activation interval and RMS peak time proposed in this study can be used as new parameters for gait analysis.
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Decker, Michael J., John M. Tokish, Henry B. Ellis, Michael R. Torry, and Richard J. Hawkins. "Subscapularis Muscle Activity during Selected Rehabilitation Exercises." American Journal of Sports Medicine 31, no. 1 (January 2003): 126–34. http://dx.doi.org/10.1177/03635465030310010601.
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Background The upper and lower portions of the subscapularis muscle are independently innervated and activated. Hypothesis Upper and lower portions of the subscapularis muscle demonstrate different activation levels and require different exercises for rehabilitation. Study Design Controlled laboratory study. Methods Fifteen healthy subjects performed seven shoulder-strengthening exercises. Electromyographic data were collected from the latissimus dorsi, teres major, pectoralis major, infraspinatus, supraspinatus, and upper and lower subscapularis muscles. Results Upper subscapularis muscle activity was greater than lower subscapularis muscle activity for all exercises except for internal rotation with 0° of humeral abduction. The push-up plus and diagonal exercises consistently stressed the upper and lower subscapularis muscles to the greatest extent. Conclusions Humeral abduction was found to have a strong influence on the selective activation of the upper versus the lower subscapularis muscle and thus supported the design of different exercise continuums. In addition, the push-up plus and diagonal exercises were found to be superior to traditional internal rotation exercises for activating both functional portions of the subscapularis muscle. Clinical Relevance Our results showing that the upper and lower portions of the subscapularis muscle are functionally independent may affect training or rehabilitation protocols for the rotator cuff muscles.
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Jacobs, Jesse V., Sharon M. Henry, Stephanie L. Jones, Juvena R. Hitt, and Janice Y. Bunn. "A history of low back pain associates with altered electromyographic activation patterns in response to perturbations of standing balance." Journal of Neurophysiology 106, no. 5 (November 2011): 2506–14. http://dx.doi.org/10.1152/jn.00296.2011.
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People with a history of low back pain (LBP) exhibit altered responses to postural perturbations, and the central neural control underlying these changes in postural responses remains unclear. To characterize more thoroughly the change in muscle activation patterns of people with LBP in response to a perturbation of standing balance, and to gain insight into the influence of early- vs. late-phase postural responses (differentiated by estimates of voluntary reaction times), this study evaluated the intermuscular patterns of electromyographic (EMG) activations from 24 people with and 21 people without a history of chronic, recurrent LBP in response to 12 directions of support surface translations. Two-factor general linear models examined differences between the 2 subject groups and 12 recorded muscles of the trunk and lower leg in the percentage of trials with bursts of EMG activation as well as the amplitudes of integrated EMG activation for each perturbation direction. The subjects with LBP exhibited 1) higher baseline EMG amplitudes of the erector spinae muscles before perturbation onset, 2) fewer early-phase activations at the internal oblique and gastrocnemius muscles, 3) fewer late-phase activations at the erector spinae, internal and external oblique, rectus abdominae, and tibialis anterior muscles, and 4) higher EMG amplitudes of the gastrocnemius muscle following the perturbation. The results indicate that a history of LBP associates with higher baseline muscle activation and that EMG responses are modulated from this activated state, rather than exhibiting acute burst activity from a quiescent state, perhaps to circumvent trunk displacements.
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Babault, Nicolas, Michel Pousson, Anne Michaut, and Jacques Van Hoecke. "Effect of quadriceps femoris muscle length on neural activation during isometric and concentric contractions." Journal of Applied Physiology 94, no. 3 (March 1, 2003): 983–90. http://dx.doi.org/10.1152/japplphysiol.00717.2002.
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The effect of muscle length on neural drive (here termed “neural activation”) was investigated from electromyographic activities and activation levels (twitch interpolation). The neural activation was measured in nine men during isometric and concentric (30 and 120°/s) knee extensions for three muscle lengths (35, 55, and 75° knee flexion, i.e., shortened, intermediate, and lengthened muscles, respectively). Long (76°), medium (56°), and short (36°) ranges of motion were used to investigate the effect of the duration of concentric contraction. Neural activation was found to depend on muscle length. Reducing the duration of contraction had no effect. Neural activation was higher with short muscle length during isometric contractions and was weaker for shortened than for intermediate and lengthened muscles performing 120°/s concentric contractions. Muscle length had no effect on 30°/s concentric neural activation. Peripheral mechanisms and discharge properties of the motoneurons could partly explain the observed differences in the muscle length effect. We thus conclude that muscle length has a predominant effect on neural activation that would modulate the angular velocity dependency.
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Miller, A. D., and S. Nonaka. "Mechanisms of abdominal muscle activation during vomiting." Journal of Applied Physiology 69, no. 1 (July 1, 1990): 21–25. http://dx.doi.org/10.1152/jappl.1990.69.1.21.
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The possible contribution of spinal reflexes to abdominal muscle activation during vomiting was assessed in decerebrate cats. The activity of these muscles is partly controlled by bulbospinal expiratory neurons in the caudal ventral respiratory group (VRG). In a previous study it was found that the abdominal muscles are still active during vomiting after midsagittal lesion of the axons of these neurons between C1 and the obex (A.D. Miller, L.K. Tan, and I. Suzuki. J. Neurophysiol. 57: 1854-1866, 1987). The present experiments indicate that this postlesion activity was due to spinal stretch reflexes because 1) such midsagittal lesions eliminate abdominal muscle nerve activity during fictive vomiting in paralyzed cats in which there are no abdominal stretch reflexes, 2) the abdominal muscles are activated during vomiting by spinal reflexes after upper thoracic cord transections, and 3) the normal 100-ms delay between diaphragmatic and abdominal activation during vomiting is reduced to approximately 20-25 ms after both types of lesions, which is consistent with postlesion abdominal reflex activation. Our results also suggest that, during normal vomiting, abdominal stretch and tension reflexes have only a minor role if any and abdominal muscle activation is probably mediated primarily or exclusively by expiratory neurons in the caudal ventral respiratory group. However, our finding that phrenic activity is reduced both during vomiting after thoracic transections and during fictive vomiting after paralysis is consistent with a contribution of reflex activity from abdominal and/or intercostal muscles to phrenic discharge during normal vomiting.
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KAK, D. W., A. R. ANITA, N. M. NIZLAN, I. NORMALA, N. A. ABDUL JALIL, and S. V. WONG. "COMPARISON OF NECK MUSCLE ELECTROMYOGRAPHY ACTIVITY IN RESPONSE TO EXTERNAL FORCE BETWEEN STATIC AND DYNAMIC LOADING." Journal of Mechanics in Medicine and Biology 19, no. 04 (June 2019): 1850034. http://dx.doi.org/10.1142/s0219519418500343.
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Understanding the behavior of neck muscles is essential to accurately simulate the human head-neck segment movement especially for low-speed motor vehicle crash situation. Some head-neck mathematical models were designed using neck muscle activation behavior in isometric contraction (static loading) as the properties of neck muscle activation. However, neck muscle activation pattern and strength capability may vary between static and dynamic loading. This study aimed to determine the differences between neck muscle activation level under static and dynamic loading. A neck strength test involving 22 human volunteers was conducted with two different tasks in extension and flexion direction with three different loads. The neck muscle activation level is determined through measuring the electromyography (EMG) responses of selected flexor and extensor muscles using surface bilateral electrode and recorded. The findings showed that neck muscle activation level was significantly greater in dynamic loading than static loading ([Formula: see text]). These implied that more efforts from neck muscles were required to resist against dynamic loading than static loading. Nonetheless, the differences in EMG activities between these two loading conditions progressively decreased when more loads were applied. This study has established an empirical model to describe the relationship between neck muscle activation level and force output for both loading condition in flexion and extension.
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Kipp, Kristof, Ron Pfeiffer, Michelle Sabick, Chad Harris, Jeanie Sutter, Seth Kuhlman, and Kevin Shea. "Muscle Synergies During a Single-Leg Drop-Landing in Boys and Girls." Journal of Applied Biomechanics 30, no. 2 (April 2014): 262–68. http://dx.doi.org/10.1123/jab.2012-0193.
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The purpose of this study was to investigate muscle activation patterns during a landing task in boys and girls through the use of muscle synergies. Electromyographical data from six lower extremity muscles were collected from 11 boys and 16 girls while they performed single-leg drop-landings. Electromyographical data from six leg muscles were rectified, smoothed, and normalized to maximum dynamic muscle activity during landing. Data from 100 ms before to 100 ms after touchdown were submitted to factor analyses to extract muscle synergies along with the associated activation and weighing coefficients. Boys and girls both used three muscle synergies. The activation coefficients of these synergies captured muscle activity during the prelanding, touchdown, and postlanding phases of the single-leg drop-landing. Analysis of the weighing coefficients indicated that within the extracted muscle synergies the girls emphasized activation of the medial hamstring muscle during the prelanding and touchdown synergy whereas boys emphasized activation of the vastus medialis during the postlanding synergy. Although boys and girls use similar muscle synergies during single-leg drop-landings, they differed in which muscles were emphasized within these synergies. The observed differences in aspects related to the muscle synergies during landing may have implications with respect to knee injury risk.
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Ravari, Reihaneh, and Hamid Reza Kobravi. "Identifying the Dynamics of Leg Muscle Activation During Human Gait Using Neural Oscillator and Fuzzy Compensator." International Clinical Neuroscience Journal 5, no. 3 (September 30, 2018): 106–12. http://dx.doi.org/10.15171/icnj.2018.21.
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Background: The goal of this study is to design a model in order to predict the muscle activation pattern because the muscle activation patterns contain valuable information about the muscle dynamics and movement patterns. Therefore, the goal of the presentation of this neural model is to identify the desired muscle activation patterns by Hopf chaotic oscillator during walking. Since the knee muscles activation has a significant effect on the movement pattern during walking, the main concentration of this study is to identify the knee muscles activation dynamics using a modeling technique. Methods: The electromyography (EMG) recording obtained from 5 healthy subjects that electrodes positioned on the tibialis-anterior (TA) and rectus femoris muscles on every 2 feet. In the proposed model, along with the chaotic oscillator, a fuzzy compensator was designed to face the unmolded dynamics. In fact, on the condition, the observed difference between the desired and actual activation patterns violate some specific quantitative ranges, the fuzzy compensator based on predefined rules modify the activity pattern produced by the Hopf oscillator. Results: Some quantitative measures used to evaluate the results. According to the achieved results, the proposed model could generate the trajectories, dynamics of which are similar to the muscle activation dynamics of the studied muscles. In this model, the generated activity pattern by the proposed model cannot follow the desired activity of the TA muscle as well as rectus femoris muscle. Conclusion: The similarity between the generated activity pattern by the model and the activation dynamics of Rectus- Femoris muscle was more in comparison with the similarity observed between activation pattern of Tibialis- Anterior and the pattern generated by the model. In other words, based on the recorded human data, the activation pattern of the Rectus- Femoris is more similar to a rhythmic pattern.
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Cugliari, Giovanni, and Gennaro Boccia. "Core Muscle Activation in Suspension Training Exercises." Journal of Human Kinetics 56, no. 1 (March 1, 2017): 61–71. http://dx.doi.org/10.1515/hukin-2017-0023.
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AbstractA quantitative observational laboratory study was conducted to characterize and classify core training exercises executed in a suspension modality on the base of muscle activation. In a prospective single-group repeated measures design, seventeen active male participants performed four suspension exercises typically associated with core training (roll-out, bodysaw, pike and knee-tuck). Surface electromyographic signals were recorded from lower and upper parts of rectus abdominis, external oblique, internal oblique, lower and upper parts of erector spinae muscles using concentric bipolar electrodes. The average rectified values of electromyographic signals were normalized with respect to individual maximum voluntary isometric contraction of each muscle. Roll-out exercise showed the highest activation of rectus abdominis and oblique muscles compared to the other exercises. The rectus abdominis and external oblique reached an activation higher than 60% of the maximal voluntary contraction (or very close to that threshold, 55%) in roll-out and bodysaw exercises. Findings from this study allow the selection of suspension core training exercises on the basis of quantitative information about the activation of muscles of interest. Roll-out and bodysaw exercises can be considered as suitable for strength training of rectus abdominis and external oblique muscles.
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Walterspacher, Stephan, Fabian Pietsch, David Johannes Walker, Kai Röcker, and Hans-Joachim Kabitz. "Activation of respiratory muscles during respiratory muscle training." Respiratory Physiology & Neurobiology 247 (January 2018): 126–32. http://dx.doi.org/10.1016/j.resp.2017.10.004.
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Wade, Logan, Glen A. Lichtwark, and Dominic J. Farris. "Joint and muscle-tendon coordination strategies during submaximal jumping." Journal of Applied Physiology 128, no. 3 (March 1, 2020): 596–603. http://dx.doi.org/10.1152/japplphysiol.00293.2019.
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Previous research has demonstrated that during submaximal jumping humans prioritize reducing energy consumption by minimizing countermovement depth. However, sometimes movement is constrained to a nonpreferred pattern, and this requires adaptation of neural control that accounts for complex interactions between muscle architecture, muscle properties, and task demands. This study compared submaximal jumping with either a preferred or a deep countermovement depth to examine how joint and muscle mechanics are integrated into the adaptation of coordination strategies in the deep condition. Three-dimensional motion capture, two force plates, electromyography, and ultrasonography were used to examine changes in joint kinetics and kinematics, muscle activation, and muscle kinematics for the lateral gastrocnemius and soleus. Results demonstrated that a decrease in ankle joint work during the deep countermovement depth was due to increased knee flexion, leading to unfavorably short biarticular muscle lengths and reduced active fascicle length change during ankle plantar flexion. Therefore, ankle joint work was likely decreased because of reduced active fascicle length change and operating position on the force-length relationship. Hip joint work was significantly increased as a result of altered muscle activation strategies, likely due to a substantially greater hip extensor muscle activation period compared with plantar flexor muscles during jumping. Therefore, coordination strategies at individual joints are likely influenced by time availability, where a short plantar flexor activation time results in dependence on muscle properties, instead of simply altering muscle activation, while the longer time for contraction of muscles at the hip allows for adjustments to voluntary neural control. NEW & NOTEWORTHY Using human jumping as a model, we show that adapting movement patterns to altered task demands is achieved differently by muscles across the leg. Because of proximal-to-distal sequencing, distal muscles (i.e., plantar flexors) have reduced activation periods and, as a result, rely on muscle contractile properties (force-length relationship) for adjusting joint kinetics. For proximal muscles that have greater time availability, voluntary activation is modulated to adjust muscle outputs.
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Sloniger, Mark A., Kirk J. Cureton, Barry M. Prior, and Ellen M. Evans. "Lower extremity muscle activation during horizontal and uphill running." Journal of Applied Physiology 83, no. 6 (December 1, 1997): 2073–79. http://dx.doi.org/10.1152/jappl.1997.83.6.2073.
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Sloniger, Mark A., Kirk J. Cureton, Barry M. Prior, and Ellen M. Evans. Lower extremity muscle activation during horizontal and uphill running. J. Appl. Physiol. 83(6): 2073–2079, 1997.—To provide more comprehensive information on the extent and pattern of muscle activation during running, we determined lower extremity muscle activation by using exercise-induced contrast shifts in magnetic resonance (MR) images during horizontal and uphill high-intensity (115% of peak oxygen uptake) running to exhaustion (2.0–3.9 min) in 12 young women. The mean percentage of muscle volume activated in the right lower extremity was significantly ( P <0.05) greater during uphill (73 ± 7%) than during horizontal (67 ± 8%) running. The percentage of 13 individual muscles or groups activated varied from 41 to 90% during horizontal running and from 44 to 83% during uphill running. During horizontal running, the muscles or groups most activated were the adductors (90 ± 5%), semitendinosus (86 ± 13%), gracilis (76 ± 20%), biceps femoris (76 ± 12%), and semimembranosus (75 ± 12%). During uphill running, the muscles most activated were the adductors (83 ± 8%), biceps femoris (79 ± 7%), gluteal group (79 ± 11%), gastrocnemius (76 ± 15%), and vastus group (75 ± 13%). Compared with horizontal running, uphill running required considerably greater activation of the vastus group (23%) and soleus (14%) and less activation of the rectus femoris (29%), gracilis (18%), and semitendinosus (17%). We conclude that during high-intensity horizontal and uphill running to exhaustion, lasting 2–3 min, muscles of the lower extremity are not maximally activated, suggesting there is a limit to the extent to which additional muscle mass recruitment can be utilized to meet the demand for force and energy. Greater total muscle activation during exhaustive uphill than during horizontal running is achieved through an altered pattern of muscle activation that involves increased use of some muscles and less use of others.
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Josephson, R. K., J. G. Malamud, and D. R. Stokes. "Asynchronous muscle: a primer." Journal of Experimental Biology 203, no. 18 (September 15, 2000): 2713–22. http://dx.doi.org/10.1242/jeb.203.18.2713.
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The asynchronous muscles of insects are characterized by asynchrony between muscle electrical and mechanical activity, a fibrillar organization with poorly developed sarcoplasmic reticulum, a slow time course of isometric contraction, low isometric force, high passive stiffness and delayed stretch activation and shortening deactivation. These properties are illustrated by comparing an asynchronous muscle, the basalar flight muscle of the beetle Cotinus mutabilis, with synchronous wing muscles from the locust, Schistocerca americana. Because of delayed stretch activation and shortening deactivation, a tetanically stimulated beetle muscle can do work when subjected to repetitive lengthening and shortening. The synchronous locust muscle, subjected to similar stimulation and length change, absorbs rather than produces work.
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HAN, KAP-SOO, CHANG HO YU, MYOUNG-HWAN KO, and TAE KYU KWON. "ANALYSIS OF THE EFFECTS OF SPINE STABILIZATION EXERCISES USING A WHOLE BODY TILT DEVICE ON MUSCLE FORCES IN THE SPINE." Journal of Mechanics in Medicine and Biology 14, no. 06 (December 2014): 1440003. http://dx.doi.org/10.1142/s021951941440003x.
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The objective of the study was to investigate the effects of 3D stabilization exercises using a whole body tilt device on forces in the trunk, such as individual muscle forces and activation patterns, maximum muscle activities and spine loads. For this sake, a musculoskeletal (MS) model of the whole body was developed, and an inverse dynamics analysis was performed to predict the forces on the spine. An EMG measurement experiment was conducted to validate the muscle forces and activation patterns. The MS model was rotated and tilted in eight different directions: anterior (A), posterior (P), anterior right (AR), posterior right (PR), anterior left (AL), posterior left (PL), right (R) and left (L), replicating the directions of the 3D spine balance exercise device, as performed in the experiment. The anterior directions of the tilt primarily induced the activation of long and superficial back muscles and the posterior directions activated the front muscles. However, deep muscles, such as short muscles and multifidi, were activated in all directions of the tilt. The resultant joint forces in the right and left directions of the tilt were the least among the directions, but higher muscle activations and more diverse muscle recruitments than other positions were observed. Therefore, these directions of tilt may be suitable for the elderly and rehabilitation patients who require muscle strengthening with less spinal loads. In the present investigation, it was shown that 3D stabilization exercises could provide considerable muscle exercise effects with a minimum perturbation of structure. The results of this study can be used to provide safety guidelines for muscle exercises using this type of tilting device. Therefore, the proposed direction of tilt can be used to strengthen targeted muscles, depending on the patients' muscular condition.
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Jakobi, Jennifer M., and Charles L. Rice. "Voluntary muscle activation varies with age and muscle group." Journal of Applied Physiology 93, no. 2 (August 1, 2002): 457–62. http://dx.doi.org/10.1152/japplphysiol.00012.2002.
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The consistency and the number of attempts required to achieve maximal voluntary muscle activation have not been documented and compared between young and old adults. Furthermore, few studies have contrasted activation between functional pairs of muscle groups, and no study has tested upper limb muscles. The purpose of this study was to measure and compare voluntary muscle activation of the elbow flexors and extensors in young and old men over two separate test sessions. With the method of twitch interpolation to measure activation, six young (24 ± 1 yr) and six old (83 ± 4 yr) men performed five maximal voluntary contractions (MVC) during each session for each muscle group. Elbow flexion and extension MVC was less (43 and 47%, respectively) in the old men, yet the best maximal voluntary muscle activation was similar between age groups. However, when all 10 attempts at MVC were compared, the mean activation scores were slightly less (∼5%) in the elbow extensors but were ∼11% less ( P < 0.001) in the elbow flexors of old men, compared with young men. During the second session, there was a significant improvement of 13% ( P< 0.005) in mean elbow flexor activation in the old men. There were no session differences for either muscle group for the young men. The results indicate that, for aged men, elbow flexor maximal activation is achieved less frequently compared with elbow extensors, and thus mean activation for elbow flexors is less than for elbow extensors. However, if sufficient attempts are provided, the best effort for the old men is not different from that of the young men for either muscle group.
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Klauer, Christian, Maximilian Irmer, and Thomas Schauer. "A muscle model for hybrid muscle activation." Current Directions in Biomedical Engineering 1, no. 1 (September 1, 2015): 386–89. http://dx.doi.org/10.1515/cdbme-2015-0094.
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AbstractTo develop model-based control strategies for Functional Electrical Stimulation (FES) in order to support weak voluntary muscle contractions, a hybrid model for describing joint motions induced by concurrent voluntary-and FES induced muscle activation is proposed. It is based on a Hammerstein model – as commonly used in feedback controlled FES – and exemplarily applied to describe the shoulder abduction joint angle. Main component of a Hammerstein muscle model is usually a static input nonlinearity depending on the stimulation intensity. To additionally incorporate voluntary contributions, we extended the static non-linearity by a second input describing the intensity of the voluntary contribution that is estimated by electromyography (EMG) measurements – even during active FES. An Artificial Neural Network (ANN) is used to describe the static input non-linearity. The output of the ANN drives a second-order linear dynamical system that describes the combined muscle activation and joint angle dynamics. The tunable parameters are adapted to the individual subject by a system identification approach using previously recorded I/O-data. The model has been validated in two healthy subjects yielding RMS values for the joint angle error of 3.56° and 3.44°, respectively.
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SHINOHARA, MINORU. "Muscle Activation Strategies in Multiple Muscle Systems." Medicine & Science in Sports & Exercise 41, no. 1 (January 2009): 181–83. http://dx.doi.org/10.1249/mss.0b013e318183c0b2.
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Fice, Jason B., Gunter P. Siegmund, and Jean-Sébastien Blouin. "Neck muscle biomechanics and neural control." Journal of Neurophysiology 120, no. 1 (July 1, 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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Roh, Jinsook, William Z. Rymer, Eric J. Perreault, Seng Bum Yoo, and Randall F. Beer. "Alterations in upper limb muscle synergy structure in chronic stroke survivors." Journal of Neurophysiology 109, no. 3 (February 1, 2013): 768–81. http://dx.doi.org/10.1152/jn.00670.2012.
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Previous studies in neurologically intact subjects have shown that motor coordination can be described by task-dependent combinations of a few muscle synergies, defined here as a fixed pattern of activation across a set of muscles. Arm function in severely impaired stroke survivors is characterized by stereotypical postural and movement patterns involving the shoulder and elbow. Accordingly, we hypothesized that muscle synergy composition is altered in severely impaired stroke survivors. Using an isometric force matching protocol, we examined the spatial activation patterns of elbow and shoulder muscles in the affected arm of 10 stroke survivors (Fugl-Meyer <25/66) and in both arms of six age-matched controls. Underlying muscle synergies were identified using non-negative matrix factorization. In both groups, muscle activation patterns could be reconstructed by combinations of a few muscle synergies (typically 4). We did not find abnormal coupling of shoulder and elbow muscles within individual muscle synergies. In stroke survivors, as in controls, two of the synergies were comprised of isolated activation of the elbow flexors and extensors. However, muscle synergies involving proximal muscles exhibited consistent alterations following stroke. Unlike controls, the anterior deltoid was coactivated with medial and posterior deltoids within the shoulder abductor/extensor synergy and the shoulder adductor/flexor synergy in stroke was dominated by activation of pectoralis major, with limited anterior deltoid activation. Recruitment of the altered shoulder muscle synergies was strongly associated with abnormal task performance. Overall, our results suggest that an impaired control of the individual deltoid heads may contribute to poststroke deficits in arm function.
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Henry, Timothy J., Scott M. Lephart, Jorge Giraldo, David Stone, and Freddie H. Fu. "The Effect of Muscle Fatigue on Muscle Force-Couple Activation of the Shoulder." Journal of Sport Rehabilitation 10, no. 4 (November 2001): 246–56. http://dx.doi.org/10.1123/jsr.10.4.246.
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Context:Muscle fatigue is an important concept in regard to the muscle function of the shoulder joint. Its effect on the muscle force couples of the glenohumeral joint has not been fully identified.Objective:To examine the effects of muscle fatigue on muscle force-couple activation in the normal shoulder.Design:Pretest, posttest.Patients:Ten male subjects, age 18–30 years, with no previous history of shoulder problems.Main Outcome Measures:EMG (area) values were assessed for the anterior and middle deltoid, subscapularis, and infraspinatus muscles during 4 dynamic stabilizing exercises before and after muscle fatigue. The exercises examined were a push-up, horizontal abduction, segmental stabilization, and rotational movement on a slide board.Results:No significant differences were observed for any of the muscles tested.Conclusions:The results of our study indicate that force-couple coactivation of the glenohumeral joint is not significantly altered after muscle fatigue.
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Dooley, Katherine, Suzanne J. Snodgrass, Peter Stanwell, Samantha Birse, Adrian Schultz, Michael K. Drew, and Suzi Edwards. "Spatial muscle activation patterns during different leg exercise protocols in physically active adults using muscle functional MRI: a systematic review." Journal of Applied Physiology 129, no. 4 (October 1, 2020): 934–46. http://dx.doi.org/10.1152/japplphysiol.00290.2020.
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An emerging method to measure muscle activation patterns is muscle functional magnetic resonance imaging (mfMRI), where preexercise and postexercise muscle metabolism differences indicate spatial muscle activation patterns. We evaluated studies employing mfMRI to determine activation patterns of lumbar or lower limb muscles following exercise in physically active adults. Electronic systematic searches were conducted until March 2020. All studies employing ≥1.5 Tesla MRI scanners to compare spatial muscle activation patterns at the level of or inferior to the first lumbar vertebra in healthy, active adults. Two authors independently assessed study eligibility before appraising methodological quality using a National Institutes of Health assessment tool. Because of heterogeneity, findings were synthesized without meta-analysis. Of the 1,946 studies identified, seven qualified for inclusion and pertained to hamstring ( n = 5), quadriceps ( n = 1) or extrinsic foot ( n = 1) muscles. All included studies controlled for internal validity, with one employing assessor blinding. MRI physics and differing research questions explain study methodology heterogeneity. Significant mfMRI findings were: following Nordic exercise, hamstrings with previous trauma (strain or surgical autograft harvest) demonstrated reduced activation compared with unharmed contralateral muscles, and asymptomatic individuals preferentially activated semitendinosus; greater biceps femoris long head to semitendinosus ratios reported following 45° hip extension over Nordic exercise; greater rectus femoris activation occurred in “flywheel” over barbell squats. mfMRI parameters differ on the basis of individual research questions. Individual muscles show greater activation following specific exercises, suggesting exercise specificity may be important for rehabilitation, although evidence is limited to single cohort studies comparing interlimb differences preexercise versus postexercise.
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Mravcsik, Mariann, Lilla Botzheim, Norbert Zentai, Davide Piovesan, and Jozsef Laczko. "The Effect of Crank Resistance on Arm Configuration and Muscle Activation Variances in Arm Cycling Movements." Journal of Human Kinetics 76, no. 1 (January 11, 2021): 175–89. http://dx.doi.org/10.2478/hukin-2021-0053.
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Abstract Arm cycling on an ergometer is common in sports training and rehabilitation protocols. The hand movement is constrained along a circular path, and the user is working against a resistance, maintaining a cadence. Even if the desired hand trajectory is given, there is the flexibility to choose patterns of joint coordination and muscle activation, given the kinematic redundancy of the upper limb. With changing external load, motor noise and changing joint stiffness may affect the pose of the arm even though the endpoint trajectory is unchanged. The objective of this study was to examine how the crank resistance influences the variances of joint configuration and muscle activation. Fifteen healthy participants performed arm cranking on an arm-cycle ergometer both unimanually and bimanually with a cadence of 60 rpm against three crank resistances. Joint configuration was represented in a 3-dimensional joint space defined by inter-segmental joint angles, while muscle activation in a 4-dimensional "muscle activation space" defined by EMGs of 4 arm muscles. Joint configuration variance in the course of arm cranking was not affected by crank resistance, whereas muscle activation variance was proportional to the square of muscle activation. The shape of the variance time profiles for both joint configuration and muscle activation was not affected by crank resistance. Contrary to the prevailing assumption that an increased motor noise would affect the variance of auxiliary movements, the influence of noise doesn’t appear at the joint configuration level even when the system is redundant. Our results suggest the separation of kinematic- and force-control, via mechanisms that are compensating for dynamic nonlinearities. Arm cranking may be suitable when the aim is to perform training under different load conditions, preserving stable and secure control of joint movements and muscle activations.
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Swynghedauw, B. "Calcium in muscle activation." FEBS Letters 242, no. 2 (January 2, 1989): 455–56. http://dx.doi.org/10.1016/0014-5793(89)80529-0.
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Frandsen, Clint R., Grayson Tarbox, Logan A. Thorneloe, A. Wayne Johnson, and Sarah T. Ridge. "Muscle Activation Signal Decay." Medicine & Science in Sports & Exercise 52, no. 7S (July 2020): 945. http://dx.doi.org/10.1249/01.mss.0000685828.31423.04.
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Kinugasa, Ryuta, Yasuo Kawakami, and Tetsuo Fukunaga. "Muscle activation and its distribution within human triceps surae muscles." Journal of Applied Physiology 99, no. 3 (September 2005): 1149–56. http://dx.doi.org/10.1152/japplphysiol.01160.2004.
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The purposes of this study were 1) to quantify the volume of activated parts within a whole muscle and 2) to examine activated area distributions along the length of muscle. Seven male subjects performed five sets of 10 repetitions of a single-leg calf-raise exercise with the knee fully extended. Transverse relaxation time (T2)-weighted spin echo images were acquired before and immediately after the exercise. A range of pixels with a T2 greater than the mean +1 SD of the region of interest (ROI) from the preexercise image and pixels with a T2 lower than the mean + SD of the ROI from the postexercise image were defined as “active” muscle. The active muscle images were three dimensionally reconstructed, from which the volume of the activated muscle was determined for individual triceps surae (TS) muscles. Our data indicate that ∼46% of the medial gastrocnemius (MG) muscle was activated during the exercise, with activation of the lateral gastrocnemius (LG) and soleus (Sol) muscles being ∼35%. In the MG, distal portions had a greater percentage area of activated muscle than the proximal portions ( P < 0.05), which was consistent with the results regarding electromyogram activity. In contrast, regional activation differences were not observed in the LG and Sol. These findings suggest that the amounts of activated muscle and its distribution would be different among TS muscles.