Abstract
Skeletal muscle is capable of changing its structural parameters, metabolic rate and functional characteristics within a wide range when adapting to various loading regimens and states of the organism. Prolonged muscle inactivation leads to serious negative consequences that affect the quality of life and work capacity of people. This review examines various conditions that lead to decreased levels of muscle loading and activity and describes the key molecular mechanisms of muscle responses to these conditions. It also details the theoretical foundations of various methods preventing adverse muscle changes caused by decreased motor activity and describes these methods. A number of recent studies presented in this review make it possible to determine the molecular basis of the countermeasure methods used in rehabilitation and space medicine for many years, as well as to identify promising new approaches to rehabilitation and to form a holistic understanding of the mechanisms of gravity force control over the muscular system.
Highlights
Skeletal muscle is an extremely flexible organ, since it undergoes various structural and functional changes in response to external and internal stimuli
This review is devoted to the description of the main changes in disused skeletal muscles and countermeasures against changes occurring under these conditions, including both widely used approaches and those just starting to be put into practice
The functional unloading of skeletal muscles occurs both in the conditions of space flight and, in one form or another, in terrestrial conditions
Summary
Skeletal muscle is an extremely flexible organ, since it undergoes various structural and functional changes in response to external and internal stimuli. A decrease in the CSA was observed only for the plantar muscle, with the limitation of activity having a greater effect on the fast-twitch muscle fibers These results differ from the earlier data obtained under the conditions of weightlessness or hindlimb unloading, which showed a greater atrophy of slow-twitch muscle fibers than fast-twitch ones [5,49]. Animals in space flight showed a significant decrease in the CSA of the vastus lateralis muscle, which was observed in animals staying on Earth, whereas the sizes of the slow-twitch fibers of the soleus muscle decreased only under conditions of space flight [60,61] These data demonstrate the different effects of supportlessness and mobility limitation for the locomotor and tonic components of the muscular system.
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