https://jneuroengrehab.biomedcentral.com/articles/10.1186/s12984-017-0310-6
- Walter HerzogEmail author
Journal of NeuroEngineering and Rehabilitation201714:98
© The Author(s). 2017
Received: 22 March 2017
Accepted: 11 September 2017
Published: 16 September 2017
Abstract
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.
Keywords
Muscle mechanics Cross-bridge Theory Sarcomeres Residual Force Enhancement Muscle Modeling Force Sharing Sliding Filament TitinBackground
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)
force-sharing 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.
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