Name: Bridging the Gap Between In Vivo and Ex Vivo Studies with the "Avatar" Technique to Advance Muscle Mechanics Research (Video) | JoVE
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Description: Watch this Scientific Journal Video about Bridging the Gap Between In Vivo and Ex Vivo Studies with the "Avatar" Technique to Advance Muscle Mechanics Research at JoVE.com

We thank Dr. Nicolai Konow for providing the data used in this study. Funded by NSF IOS-2016049 and NSF DBI-2021832.

All animal studies were approved by the Institutional Animal Care and Use Committee at Northern Arizona University. Extensor digitorum longus (EDL) muscles from male and female wild-type mice (strain B6C3Fe a/a-Ttnmdm/J), aged 60-280 days, were used for the present study. The animals were obtained from a commercial source (see Table of Materials), and established in a colony at Northern Arizona University.
1. Selecting in vivo strain trajectory and p...

“Avatar”- Optimized Ex Vivo Work Loop Experiment to Emulate In Vivo Muscle Force

<ol>
	<li>Dickinson, M. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+Animals+move:+an+integrative+view.">How Animals move: an integrative view.</a> Science. 288 (5463), 100-106 (2000).</li><li>Sponberg, S., Abbott, E., Sawicki, G. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Perturbing+the+muscle+work+loop+paradigm+to+unravel+the+neuromechanics+of+unsteady+locomotion.">Perturbing the muscle work loop paradigm to unravel the neuromechanics of unsteady locomotion.</a> Journal of Experimental Biology. 226 (7), 243561 (2023).</li><li>Daley, M. A., Biewener, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Running+over+rough+terrain+reveals+limb+control+for+intrinsic+stability.">Running over rough terrain reveals limb control for intrinsic stability.</a> Proceedings of the National Academy of Sciences. 103 (42), 15681-15686 (2006).</li><li>Daley, M. A., Usherwood, J. R., Felix, G., Biewener, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Running+over+rough+terrain:+guinea+fowl+maintain+dynamic+stability+despite+a+large+unexpected+change+in+substrate+height.">Running over rough terrain: guinea fowl maintain dynamic stability despite a large unexpected change in substrate height.</a> Journal of Experimental Biology. 209 (1), 171-187 (2006).</li><li>Daley, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+the+agility+of+running+birds:+Sensorimotor+and+mechanical+factors+in+avian+bipedal+locomotion.">Understanding the agility of running birds: Sensorimotor and mechanical factors in avian bipedal locomotion.</a> Integrative and Comparative Biology. 58 (5), 884-893 (2018).</li><li>Biewener, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Animal locomotion. , (2003).</li><li>Robertson, B. D., Sawicki, G. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Unconstrained+muscle-tendon+workloops+indicate+resonance+tuning+as+a+mechanism+for+elastic+limb+behavior+during+terrestrial+locomotion.">Unconstrained muscle-tendon workloops indicate resonance tuning as a mechanism for elastic limb behavior during terrestrial locomotion.</a> Proceedings of the National Academy of Sciences. 112 (43), E5891-E5898 (2015).</li><li>Josephson, R. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+power+output+from+striated+muscle+during+cyclic+contraction.">Mechanical power output from striated muscle during cyclic contraction.</a> The Journal of Experimental Biology. 114, 493-512 (1985).</li><li>Ahn, A. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+muscles+function+-+the+work+loop+technique.">How muscles function - the work loop technique.</a> Journal of Experimental Biology. 215 (7), 1051-1052 (2012).</li><li>Sawicki, G. S., Robertson, B. D., Azizi, E., Roberts, T. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Timing+matters:+tuning+the+mechanics+of+a+muscle-tendon+unit+by+adjusting+stimulation+phase+during+cyclic+contractions.">Timing matters: tuning the mechanics of a muscle-tendon unit by adjusting stimulation phase during cyclic contractions.</a> Journal of Experimental Biology. 218 (19), 3150-3159 (2015).</li><li>Libby, T., Chukwueke, C., Sponberg, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=History-dependent+perturbation+response+in+limb+muscle.">History-dependent perturbation response in limb muscle.</a> Journal of Experimental Biology. 223 (1), (2020).</li><li>Askew, G. N., Marsh, R. L., Ellington, C. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+mechanical+power+output+of+the+flight+muscles+of+blue-breasted+quail+(+Coturnix+chinensis+)+during+take-off.">The mechanical power output of the flight muscles of blue-breasted quail ( Coturnix chinensis ) during take-off.</a> Journal of Experimental Biology. 204 (21), 3601-3619 (2001).</li><li>Sponberg, S., Libby, T., Mullens, C. H., Full, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Shifts+in+a+single+muscle's+control+potential+of+body+dynamics+are+determined+by+mechanical+feedback.">Shifts in a single muscle's control potential of body dynamics are determined by mechanical feedback.</a> Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 366 (1570), 1606-1620 (2011).</li><li>Loeb, G. E., Brown, I. E., Cheng, E. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+hierarchical+foundation+for+models+of+sensorimotor+control.">A hierarchical foundation for models of sensorimotor control.</a> Experimental Brain Research. 126 (1), 1-18 (1999).</li><li>Wakeling, J. M., Tijs, C., Konow, N., Biewener, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modeling+muscle+function+using+experimentally+determined+subject-specific+muscle+properties.">Modeling muscle function using experimentally determined subject-specific muscle properties.</a> Journal of Biomechanics. 117, 110242 (2021).</li><li>The Mathworks. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MATLAB:R2021a.">MATLAB:R2021a.</a> The Mathworks. , (2021).</li><li>Tenan, M. S., Tweedell, A. J., Haynes, C. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+statistical+and+standard+algorithms+for+detecting+muscle+onset+with+surface+electromyography.">Analysis of statistical and standard algorithms for detecting muscle onset with surface electromyography.</a> PLOS ONE. 12 (5), 0177312 (2017).</li><li>Roberts, T. J., Gabald&#243;n, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interpreting+muscle+function+from+EMG:+lessons+learned+from+direct+measurements+of+muscle+force.">Interpreting muscle function from EMG: lessons learned from direct measurements of muscle force.</a> Integrative and Comparative Biology. 48 (2), 312-320 (2008).</li><li>Rice, N., Bemis, C. M., Daley, M. A., Nishikawa, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+muscle+function+during+perturbed+in+vivo+locomotion+using+a+muscle+avatar+approach.">Understanding muscle function during perturbed in vivo locomotion using a muscle avatar approach.</a> Journal of Experimental Biology. 226 (13), 244721 (2023).</li><li>Silva Cornachione, A., Ca&#231;&#227;oOliveiraBenedini-Elias, P., Cristina Polizello , P., C&#233;sar Carvalho, L., Cl&#225;udiaMattiello-Sverzut, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+Fiber+types+in+different+muscles+of+the+hindlimb+in+female+weanling+and+adult+wistar+rats.">Characterization of Fiber types in different muscles of the hindlimb in female weanling and adult wistar rats.</a> Acta Histochemica Et Cytochemica. 44 (2), 43-50 (2011).</li><li>H&#228;m&#228;l&#228;inen, N., Pette, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+histochemical+profiles+of+fast+fiber+types+IIB,+IID,+and+IIA+in+skeletal+muscles+of+mouse,+rat,+and+rabbit.">The histochemical profiles of fast fiber types IIB, IID, and IIA in skeletal muscles of mouse, rat, and rabbit.</a> Journal of Histochemistry &amp; Cytochemistry. 41 (5), 733-743 (1993).</li><li>Charles, J. P., Cappellari, O., Spence, A. J., Hutchinson, J. R., Wells, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Musculoskeletal+geometry,+muscle+architecture+and+functional+specialisations+of+the+mouse+hindlimb.">Musculoskeletal geometry, muscle architecture and functional specialisations of the mouse hindlimb.</a> PLOS ONE. 11 (4), 0147669 (2016).</li><li>Nishikawa, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Titin:+A+Tunable+spring+in+active+muscle.">Titin: A Tunable spring in active muscle.</a> Physiology (Bethesda, Md). 35 (3), 209-217 (2020).</li><li>Dick, T. J. M., Biewener, A. A., Wakeling, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+human+gastrocnemius+forces+predicted+by+Hill-type+muscle+models+and+estimated+from+ultrasound+images).">Comparison of human gastrocnemius forces predicted by Hill-type muscle models and estimated from ultrasound images).</a> The Journal of Experimental Biology. 220, 1643-1653 (2017).</li><li>Daley, M. A., Biewener, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Leg+muscles+that+mediate+stability:+mechanics+and+control+of+two+distal+extensor+muscles+during+obstacle+negotiation+in+the+guinea+fowl.">Leg muscles that mediate stability: mechanics and control of two distal extensor muscles during obstacle negotiation in the guinea fowl.</a> Philosophical Transactions of the Royal Society B: Biological Sciences. 366 (1570), 1580-1591 (2011).</li><li>Seth, A., Sherman, M., Reinbolt, J. A., Delp, S. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=OpenSim:+a+musculoskeletal+modeling+and+simulation+framework+for+in+silico+investigations+and+exchange.">OpenSim: a musculoskeletal modeling and simulation framework for in silico investigations and exchange.</a> Procedia IUTAM. 2, 212-232 (2011).</li><li>Sandercock, T. G., Heckman, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Doublet+potentiation+during+eccentric+and+concentric+contractions+of+cat+soleus+muscle.">Doublet potentiation during eccentric and concentric contractions of cat soleus muscle.</a> Journal of Applied Physiology. 82 (4), 1219-1228 (1997).</li><li>Marsh, R. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+muscles+deal+with+real-world+loads:+the+influence+of+length+trajectory+on+muscle+performance.">How muscles deal with real-world loads: the influence of length trajectory on muscle performance.</a> The Journal of Experimental Biology. 202, 3377-3385 (1999).</li><li>Hessel, A. L., Monroy, J. A., Nishikawa, K. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Non-cross+bridge+viscoelastic+elements+contribute+to+muscle+force+and+work+during+stretch-shortening+cycles:+evidence+from+whole+muscles+and+permeabilized+fibers.">Non-cross bridge viscoelastic elements contribute to muscle force and work during stretch-shortening cycles: evidence from whole muscles and permeabilized fibers.</a> Frontiers in Physiology. 12, 648019 (2021).</li><li>Lindstedt, S., Nishikawa, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Huxleys'+missing+filament:+form+and+function+of+titin+in+vertebrate+striated+muscle.">Huxleys' missing filament: form and function of titin in vertebrate striated muscle.</a> Annual Review of Physiology. 79, 145-166 (2017).</li><li>Abbate, F., De Ruiter, C. J., Offringa, C., Sargeant, A. J., De Haan, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+situ+rat+fast+skeletal+muscle+is+more+efficient+at+submaximal+than+at+maximal+activation+levels.">In situ rat fast skeletal muscle is more efficient at submaximal than at maximal activation levels.</a> Journal of Applied Physiology. 92 (5), 2089-2096 (2002).</li><li>Eng, C. M., Smallwood, L. H., Rainiero, M. P., Lahey, M., Ward, S. R., Lieber, R. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scaling+of+muscle+architecture+and+fiber+types+in+the+rat+hindlimb.">Scaling of muscle architecture and fiber types in the rat hindlimb.</a> Journal of Experimental Biology. 211 (14), 2336-2345 (2008).</li><li>Manuel, M., Chardon, M., Tysseling, V., Heckman, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scaling+of+motor+output,+from+mouse+to+humans.">Scaling of motor output, from mouse to humans.</a> Physiology (Bethesda, Md). 34 (1), 5-13 (2019).</li><li>Zajac, F. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Muscle+and+tendon:+properties,+models,+scaling,+and+application+to+biomechanics+and+motor+control.">Muscle and tendon: properties, models, scaling, and application to biomechanics and motor control.</a> Critical Reviews in Biomedical Engineering. 17 (4), 359-411 (1989).</li><li>Rice, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+muscle+function+during+in+vivo+locomotion+using+a+novel+muscle+avatar+approach.">Understanding muscle function during in vivo locomotion using a novel muscle avatar approach.</a> ProQuest Dissertations and Theses. , (2020).</li></ol>

While organisms move seamlessly across landscapes, the underlying loads and strains that the muscles experience vary drastically1,6,23. During both in vivo locomotion1,24 and in &#34;avatar&#34; experiments, muscles are stimulated submaximally under cyclical, non-steady conditions. The isometric force-length and isotonic force-velocity relationships are not well...

Moving animals achieve impressive athletic feats of endurance, speed, and agility in complex environments. Animal locomotion is particularly impressive in contrast to human-engineered machines-the stability and agility of current-legged robots, prostheses, and exoskeletons remain poor compared to animals. Legged locomotion in natural terrain requires precise control and rapid adjustments to alter the speed and maneuver environmental features that act as unexpected perturbations1,2,3,4. Yet, understanding non-steady locomotion is inherently challenging because the dynamics depend on complex interactions between the physical environment, musculoskeletal mechanics, and sensorimotor control1,2. Legged locomotion requires responding to unexpected perturbations with rapid multi-modal processing of sensory information and coordinated actuation of limbs and joints1,5. Ultimately, movement is made possible by muscles producing force via intrinsic mechanical properties of the musculoskeletal system as well as from neural control1,5,6,7. An outstanding question of neuromechanics is how these factors interact to produce coordinated movement in response to unexpected perturbations. The following technique utilizes muscle&#39;s intrinsic mechanical response to deformation using in vivo strain trajectories during controllable ex vivo experiments with an &#34;avatar&#34; muscle.
The muscle work loop technique has provided an important framework for understanding intrinsic muscle mechanics during cyclical movements8,9,10. The traditional work loop technique drives muscles through predefined, typically sinusoidal, strain trajectories using frequencies and activation patterns measured during in vivo experiments2,8,9,11. Using sinusoidal length trajectories can realistically estimate work and power output during flight12 and swimming2 under conditions where animals do not undergo rapid changes in strain trajectories due to interaction with the environment and musculoskeletal kinematics. However, in vivo muscle strain trajectories during legged locomotion arise dynamically from interactions among neural activation, musculoskeletal kinematics, and loads applied by the environment5,7,13,14. A more realistic work loop technique is needed to emulate loads, strain trajectories, and force production that corresponds to in vivo muscle-tendon dynamics and provides insight into how intrinsic muscle mechanics and neural control interact to produce coordinated movement in the face of perturbations.
Here, we present a novel way to emulate in vivo muscle forces during treadmill locomotion by using an &#34;avatar&#34; muscle from a laboratory rodent during controlled ex vivo experiments with in vivo strain trajectories that represent time-varying in vivo loads. Using the measured in vivo strain trajectories from a target muscle on muscles from a laboratory animal during controlled ex vivo experiments will emulate loads experienced during locomotion. In the experiments described here, the ex vivo mouse extensor digitorum longus (EDL) muscle is used as an &#34;avatar&#34; for the in vivo rat medial gastrocnemius (MG) muscle during walking, trotting, and galloping on a treadmill13. This approach is similar to the work-loop technique, except that in vivo strain trajectories are scaled appropriately and imposed on ex vivo mouse muscles attached to a servo motor. While mouse EDL muscles differ in size, fiber type, and architecture compared to the rat MG, it is possible to control for these differences. The &#34;avatar&#34; technique allows one to: (1) emulate in vivo strain, activation, stride frequency, and work-loop patterns; (2) vary these patterns to match in vivo force responses most accurately; and (3) vary specific features of strain and/or activation in controlled combinations to test mechanistic hypotheses.

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			<td>Jackson Laboratory</td>
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"avatar", a modified ex vivo work loop experiments using in vivo strain and activation

Movement behaviors are emergent features of dynamic systems that result from muscle force production and work output. The interplay between neural and mechanical systems occurs at all levels of biological organization concurrently, from the tuning of leg muscle properties while running to the dynamics of the limbs interacting with the ground. Understanding the conditions under which animals shift their neural control strategies toward intrinsic muscle mechanics (&#39;preflexes&#39;) in the control hierarchy would allow muscle models to predict in vivo muscle force and work more accurately. To understand in vivo muscle mechanics, ex vivo investigation of muscle force and work under dynamically varying strain and loading conditions similar to in vivo locomotion is required. In vivo strain trajectories typically exhibit abrupt changes (i.e., strain and velocity transients) that arise from interactions among neural activation, musculoskeletal kinematics, and loads applied by the environment. The principal goal of our &#34;avatar&#34; technique is to investigate how muscles function during abrupt changes in strain rate and loading when the contribution of intrinsic mechanical properties to muscle force production may be highest. In the &#34;avatar&#34; technique, the traditional work-loop approach is modified using measured in vivo strain trajectories and electromyographic (EMG) signals from animals during dynamic movements to drive ex vivo muscles through multiple stretch-shortening cycles. This approach is similar to the work-loop technique, except that in vivo strain trajectories are scaled appropriately and imposed on ex vivo mouse muscles attached to a servo motor. This technique allows one to: (1) emulate in vivo strain, activation, stride frequency, and work-loop patterns; (2) vary these patterns to match in vivo force responses most accurately; and (3) vary specific features of strain and/or activation in controlled combinations to test mechanistic hypotheses.

"Avatar", a Modified Ex vivo Work Loop Experiments Using In vivo Strain and Activation

The goal of the &#34;avatar&#34; experiments is to replicate in vivo force production and work output as closely as possible during ex vivo work loop experiments. This study chose to use mouse EDL as an &#34;avatar&#34; for rat MG because mouse EDL and rat MG are both comprised of mostly of fast-twitch muscles20,21. Both muscles are primary movers of the ankle joint (EDL ankle dorsiflexor, MG ankle plantarflexor) with similar pennation angles (m...

Watch this Scientific Journal Video about Bridging the Gap Between In Vivo and Ex Vivo Studies with the "Avatar" Technique to Advance Muscle Mechanics Research at JoVE.com

Bridging the Gap Between In Vivo and Ex Vivo Studies with the "Avatar" Technique to Advance Muscle Mechanics Research (Video) | JoVE

This article details the methodology for emulating in vivo muscle force production during ex vivo work loop experiments using an "avatar" muscle from a laboratory rodent to assess the contributions of strain transients and activation to the muscle force response.

Movement behaviors are emergent features of dynamic systems that result from muscle force production and work output. The interplay between neural and ...