Skeletal muscle mechanics: questions, problems and possible solutions

Journal of NeuroEngineering and Rehabilitation, Sep 2017

Skeletal muscle mechanics have been studied ever since people have shown an interest in human movement. However, our understanding of muscle contraction and muscle mechanical properties has changed fundamentally with the discovery of the sliding filament theory in 1954 and associated cross-bridge theory in 1957. Nevertheless, experimental evidence suggests that our knowledge of the mechanisms of contraction is far from complete, and muscle properties and muscle function in human movement remain largely unknown. In this manuscript, I am trying to identify some of the crucial challenges we are faced with in muscle mechanics, offer possible solutions to questions, and identify problems that might be worthwhile exploring in the future. Since it is impossible to tackle all (worthwhile) problems in a single manuscript, I identified three problems that are controversial, important, and close to my heart. They may be identified as follows: (i) mechanisms of muscle contraction, (ii) in vivo whole muscle mechanics and properties, and (iii) force-sharing among synergistic muscles. These topics are fundamental to our understanding of human movement and movement control, and they contain a series of unknowns and challenges to be explored in the future. It is my hope that this paper may serve as an inspiration for some, may challenge current beliefs in selected areas, tackle important problems in the area of muscle mechanics, physiology and movement control, and may guide and focus some of the thinking of future muscle mechanics research.

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Skeletal muscle mechanics: questions, problems and possible solutions

Herzog Journal of NeuroEngineering and Rehabilitation Skeletal muscle mechanics: questions, problems and possible solutions Walter Herzog 0 0 Faculty of Kinesiology, University of Calgary , 2500 University Dr, Calgary, AB T2N-1N4 , Canada Skeletal muscle mechanics have been studied ever since people have shown an interest in human movement. However, our understanding of muscle contraction and muscle mechanical properties has changed fundamentally with the discovery of the sliding filament theory in 1954 and associated cross-bridge theory in 1957. Nevertheless, experimental evidence suggests that our knowledge of the mechanisms of contraction is far from complete, and muscle properties and muscle function in human movement remain largely unknown. In this manuscript, I am trying to identify some of the crucial challenges we are faced with in muscle mechanics, offer possible solutions to questions, and identify problems that might be worthwhile exploring in the future. Since it is impossible to tackle all (worthwhile) problems in a single manuscript, I identified three problems that are controversial, important, and close to my heart. They may be identified as follows: (i) mechanisms of muscle contraction, (ii) in vivo whole muscle mechanics and properties, and (iii) force-sharing among synergistic muscles. These topics are fundamental to our understanding of human movement and movement control, and they contain a series of unknowns and challenges to be explored in the future. It is my hope that this paper may serve as an inspiration for some, may challenge current beliefs in selected areas, tackle important problems in the area of muscle mechanics, physiology and movement control, and may guide and focus some of the thinking of future muscle mechanics research. Muscle mechanics; Cross-bridge Theory; Sarcomeres; Residual Force Enhancement; Muscle Modeling; Force Sharing; Sliding Filament; Titin Background On June 12–16, 2016, approximately 150 scientists in the areas of biomechanics and neural control of movement met at the Deer Creek Lodge in Sterling Ohio for an unusual meeting. The meeting was unusual since it only had happened once before, 20 years earlier, and it was unusual because half of the available time was set aside for discussion, thus the ratio of discussion time vs. presentation time was highly favorable for those who like to discuss things. I was invited to this conference with the mandate to chair a session on skeletal muscle mechanics, energetics and plasticity. The task given to me was to identify some of the major questions and problems in skeletal muscle mechanics and present those in a concise manner and understandable to the non-expert. I must admit this was a rather difficult task for a person like me who believes that we know little to nothing about muscle contraction (on the molecular level), what the basic muscle properties are (except for the most standardized conditions), and how muscles function in the in vivo, freely moving system under non-steady-state, submaximal conditions. In the end, I identified three topics that I presented and discussed. These topics, in my opinion, comprise some of the most relevant questions in muscle mechanics and movement control, but they do not comprise, by any means, the full set of questions/problems in this area of research. At the end, I settled on topics that are highly controversial, often misunderstood, and close to my heart. They may be summarized as follows: (i) Mechanisms of muscle contraction, sarcomere stability and mechanics, (ii) whole muscle mechanics and muscle properties, and (iii) forcesharing among synergistic muscles. In the following, I will be discussing these topics concisely by raising one or more problems in the area, provide possible solutions, and may make some suggestions for future challenges that, if solved, may improve our understanding of skeletal muscle biomechanics and movement control. Following my introductory manuscript will be four manuscripts supplied by the participants of the muscle workshop: Drs. Rick Lieber, Tom Roberts, Silvia Blemker and Sabrina Lee. Their contributions are focused on specific problems and challenges faced today by researchers in muscle mechanics and they will add important considerations to the discussion below. I sincerely hope that the BANCOM conference will be repeated in another twenty years, and that we can reflect on which of the challenges, questions and problems have been solved. Hopefully, the set of papers presented here will form a framework for what some of the young people entering this field may consider worthwhile projects. Mechanisms of muscle contraction, sarcomere stability and mechanics The cross-bridge theory (description) When opening a textbook of muscle physiology and searching for how muscles contract, we are inevitably exposed to the cross-bridge theory of contraction. This theory was first proposed in a rather obscure journal (Progress in Biophysics (...truncated)


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Walter Herzog. Skeletal muscle mechanics: questions, problems and possible solutions, Journal of NeuroEngineering and Rehabilitation, 2017, pp. 98, DOI: 10.1186/s12984-017-0310-6