title: Human soleus single muscle fiber function with exercise or nutrition countermeasures during 60 days of bed rest.
abstract: 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 exercise (RE), a known hypertrophic stimulus. We hypothesized that a concurrent exercise program (AE + 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 = 7), nutrition (BRN; n = 8), and exercise (BRE; n = 6) group. Single muscle fiber diameter (Dia), peak force (Po), contractile velocity, and power were studied. BR decreased (P < 0.05) MHC I Dia (-14%), Po (-38%), and power (-39%) with no change in contractile velocity. Changes in MHC I size (-13%) and contractile function (approximately 30%) from BRN were similar to BR. BRE decreased (P < 0.05) MHC I Dia (-13%) and Po (-23%), while contractile velocity increased (P < 0.05) 26% and maintained power. These soleus muscle data show 1) the AE + 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.
authors: Human Performance Laboratory, Ball State University, Muncie, IN 47306, USA. strappe@bsu.edu
authors: Scott
authors: S
authors: Trappe
authors: Andrew
authors: A
authors: Creer
authors: Kiril
authors: K
authors: Minchev
authors: Dustin
authors: D
authors: Slivka
authors: Emily
authors: E
authors: Louis
authors: Nicholas
authors: N
authors: Luden
authors: Todd
authors: T
authors: Trappe
mesh_terms: D000328:Adult; D001510:Bed Rest / Q000009:adverse effects*; D015444:Exercise / Q000502:physiology*; D005260:Female; D018475:Head-Down Tilt; D006801:Humans; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000166:cytology / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000378:metabolism; D018994:Myosin Light Chains / Q000378:metabolism; D009747:Nutritional Physiological Phenomena / Q000502:physiology*; D018544:Weightlessness Countermeasures
chemical_list: D018994:Myosin Light Chains; D018995:Myosin Heavy Chains