Unilateral lower limb suspension does not mimic bed rest or spaceflight effects on human muscle fiber function

• Published in: Journal of applied physiology (1985) 2002-07, Vol.93 (1), p.354-360
• Main Authors: Widrick, J. J, Trappe, S. W, Romatowski, J. G, Riley, D. A, Costill, D. L, Fitts, R. H
• Format: Article
• Language: English
• Subjects: Adult; Aerospace Medicine; Bed Rest; Biological and medical sciences; Calcium - physiology; Female; Functional Laterality - physiology; Fundamental and applied biological sciences. Psychology; Humans; Leg - physiology; Legs; Male; Muscle Contraction - physiology; Muscle Fibers, Skeletal - physiology; Muscle Fibers, Slow-Twitch - physiology; Muscle, Skeletal - cytology; Muscle, Skeletal - physiology; Muscle, Skeletal - ultrastructure; Muscular system; Space Flight; Space life sciences; Striated muscle. Tendons; Vertebrates: osteoarticular system, musculoskeletal system; Weightlessness; Weightlessness Simulation
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.01245.2001

1  Department of Biology, Marquette University, Milwaukee, Wisconsin 53201; 2  Human Performance Laboratory, Ball State University, Muncie, Indiana 47306; and 3  Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin 53226 We used Ca 2+ -activated skinned muscle fibers to test the hypothesis that unilateral lower leg suspension (ULLS) alters cross-bridge mechanisms of muscle contraction. Soleus and gastrocnemius biopsies were obtained from eight subjects before ULLS, immediately after 12 days of ULLS (post-0 h), and after 6 h of reambulation (post-6 h). Post-0 h soleus fibers expressing type I myosin heavy chain (MHC) showed significant reductions in diameter, absolute and specific peak Ca 2+ -activated force, unloaded shortening velocity, and absolute and normalized peak power. Fibers obtained from the gastrocnemius were less affected by ULLS, particularly fibers expressing fast MHC isoforms. Post-6 h soleus fibers produced less absolute and specific peak force than did post-0 h fibers, suggesting that reambulation after ULLS induced cell damage. Like bed rest and spaceflight, ULLS primarily affects soleus over gastrocnemius fibers. However, in contrast to these other models, slow soleus fibers obtained after ULLS showed a decrease in unloaded shortening velocity and a greater reduction in specific force. muscle atrophy; muscle disuse; muscle damage; weightlessness