Myocellular Responses to Concurrent Flywheel Training during 70 Days of Bed Rest

Purpose This investigation evaluated myocellular responses to an integrated resistance and aerobic training program during 70 d of bed rest. Methods Training was 6 d·wk−1 on a small-footprint gravity-independent flywheel resistance and aerobic device; 3 d of maximal flywheel supine quadriceps and calf exercises with continuous rowing separated by 4 to 6 h, and 3 d of interval rowing. Vastus lateralis (VL) and soleus (SOL) muscle biopsies were obtained from eight healthy males (age, 28 ± 4 yr; BMI, 25 ± 3 kg·m−2; V˙O2max, 42 ± 6 mL·kg−1·min−1) before and after 6° head-down tilt bed rest. Vastus lateralis and SOL myosin heavy chain (MHC) I and IIa single muscle fiber size and functional characteristics, as well as overall fiber type distribution, capillarization, and metabolic enzyme activities were evaluated. Results In the VL, MHC I size and power (absolute and normalized) were preserved. The MHC IIa fibers hypertrophied (+6%, P

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