Maximal and submaximal forces of slow fibers in human soleus after bed rest

Citation
K. Yamashita-goto et al., Maximal and submaximal forces of slow fibers in human soleus after bed rest, J APP PHYSL, 91(1), 2001, pp. 417-424
Citations number
50
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physiology
Journal title
JOURNAL OF APPLIED PHYSIOLOGY
ISSN journal
8750-7587 → ACNP
Volume
91
Issue
1
Year of publication
2001
Pages
417 - 424
Database
ISI
SICI code
8750-7587(200107)91:1<417:MASFOS>2.0.ZU;2-5
Abstract
The effects of 2 and 4 mo of bed rest, with or without exercise countermeas ures, on the contractile properties of slow fibers in the human soleus musc le 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 Ca2+ concentration required for h alf-maximal activation (pCa(50)) also decreased after 2 and 4 mo of bed res t. In contrast, maximum unloaded shortening velocity (V-o) was increased af ter 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 Vo 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 unloa ding of the plantar flexors with (Penguin-1) or without (Penguin-2) placing the elastic loading elements of the suit, respectively, were investigated during similar to2 mo of bed rest. In the Penguin-1 group, mean fiber diame ter, 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 b ed rest were not prevented in the Penguin-2 group, although the degree of t he changes was less than those induced by bed rest without any countermeasu re. These results indicate that long-term bed rest results in reductions of fiber size, force-generation capacity, and Ca2+ sensitivity, and enhanceme nt of shortening velocity in slow fibers of the soleus. The data indicate t hat continuous mechanical loading on muscle, such as stretching of muscle, is an effective countermeasure for the prevention of muscular adaptations t o gravitational unloading.