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)