In:
Journal of Applied Physiology, American Physiological Society, Vol. 91, No. 1 ( 2001-07-01), p. 417-424
Abstract:
The effects of 2 and 4 mo of bed rest, with or without exercise countermeasures, on the contractile properties of slow fibers in the human soleus muscle were examined. Mean fiber diameters were 8 and 36% smaller after 2 and 4 mo of bed rest, respectively, than the pre-bed rest level. Maximum tetanic force (P o ), maximum activated force (F max ) per cross-sectional area (CSA), and the common-logarithm value of free Ca 2+ concentration required for half-maximal activation (pCa 50 ) also decreased after 2 and 4 mo of bed rest. In contrast, maximum unloaded shortening velocity ( V o ) was increased after 2 and 4 mo of bed rest. After 1 mo of recovery, fiber diameters, P o , F max per CSA ( P 〉 0.05), and pCa 50 were increased and V o decreased toward pre-bed rest levels. Effects of knee extension/flexion exercise by wearing an anti-G Penguin suit for 10 h daily, and the effects of loading or unloading of the plantar flexors with (Penguin-1) or without (Penguin-2) placing the elastic loading elements of the suit, respectively, were investigated during ∼2 mo of bed rest. In the Penguin-1 group, mean fiber diameter, P o , F max per CSA, V o , and pCa 50 were similar before and after bed rest. However, the responses of fiber size and contractile properties to bed rest were not prevented in the Penguin-2 group, although the degree of the changes was less than those induced by bed rest without any countermeasure. These results indicate that long-term bed rest results in reductions of fiber size, force-generation capacity, and Ca 2+ sensitivity, and enhancement of shortening velocity in slow fibers of the soleus. The data indicate that continuous mechanical loading on muscle, such as stretching of muscle, is an effective countermeasure for the prevention of muscular adaptations to gravitational unloading.
Type of Medium:
Online Resource
ISSN:
8750-7587
,
1522-1601
DOI:
10.1152/jappl.2001.91.1.417
Language:
English
Publisher:
American Physiological Society
Publication Date:
2001
detail.hit.zdb_id:
1404365-8
SSG:
12
SSG:
31
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