Human soleus single muscle fiber function with exercise or nutrition countermeasures during 60 days of bed rest
American Journal of Physiology. Regulatory Integrative and Comparative Physiology
Trappe S, Creer A, Minchev K, Slivka D, Louis E, Luden N, Trappe T. Human soleus single muscle fiber function with exercise or nutrition countermeasures during 60 days of bed rest. The soleus muscle has been consistently shown to atrophy more than other leg muscles during unloading and is difficult to protect using various exercise countermeasure paradigms. However, the efficacy of aerobic exercise, a known stimulus for oxidative adaptations, has not been tested in combination with resistance
... n with resistance exercise (RE), a known hypertrophic stimulus. We hypothesized that a concurrent exercise program (AE ϩ RE) would preserve soleus fiber myosin heavy chain (MHC) I size and function during 60 days of bed rest. A secondary objective was to test the hypothesis that a leucine-enriched high protein diet would partially protect soleus single fiber characteristics. Soleus muscle biopsies were obtained before and after bed rest from a control (BR; n ϭ 7), nutrition (BRN; n ϭ 8), and exercise (BRE; n ϭ 6) group. Single muscle fiber diameter (Dia), peak force (Po), contractile velocity, and power were studied. BR decreased (P Ͻ 0.05) MHC I Dia (Ϫ14%), Po (Ϫ38%), and power (Ϫ39%) with no change in contractile velocity. Changes in MHC I size (Ϫ13%) and contractile function (ϳ30%) from BRN were similar to BR. BRE decreased (P Ͻ 0.05) MHC I Dia (Ϫ13%) and Po (Ϫ23%), while contractile velocity increased (P Ͻ 0.05) 26% and maintained power. These soleus muscle data show 1) the AE ϩ RE exercise program maintained MHC I power but not size and strength, and 2) the nutrition countermeasure did not benefit single fiber size and contractile function. The divergent response in size and functional MHC I soleus properties with the concurrent exercise program was a unique finding further highlighting the challenges of protecting the unloaded soleus. R939 RE ϭ 56 min total contraction time (thigh ϭ 23 min; calf ϭ 33 min) AE ϭ ϳ24.2 h of activity (range ϭ 40-80% VO2peak) Exercise constituted ϳ1.75% of total bed rest time RE, resistance exercise; AE, aerobic exercise.