General and contractile proteins in the vastus lateralis and soleus muscles of women after 59d of bedrest with or without exercise or nutrition countermeasures

We recently reported that muscle atrophy in women after 2 months of bed rest was significantly greater than men after 3 months of bed rest. Men were able preserve myosin and actin concentrations in the vastus lateralis (VL) and soleus (SOL), despite significant atrophy (−18 to −29%) or complete (VL) or partial (SOL) preservation of muscle with resistance exercise. Concentrations of general muscle protein pools (mixed, MP; sarcoplasmic, SP; myofibrillar, MF) were maintained in the VL but preferentially lost in the SOL. We hypothesized the greater atrophy in women would lead to dysregulation of the protein pools and specific contractile proteins. Concentrations (μg/mg muscle wet weight) of MP, SP, MF, myosin, and actin were measured in 24 women before and after 59 d of 6° head down tilt bed rest with no countermeasure (BR, n=8), bed rest with resistance and aerobic training (BRE, n=8) or bed rest with high‐protein, leucine‐enriched nutrition (BRN, n=8). BR and BRN induced atrophy in the thigh and calf (BR: −21(1, −29(1%; BRN: −24(2, −28(1%); BRE maintained the thigh and partially saved the calf (−8(1%). Despite these changes, concentrations of the general protein fractions, myosin, and actin were unaltered in all conditions. Women are able to regulate general and specific contractile muscle protein content during atrophy (BR, BRN) and attenuated atrophy via exercise countermeasures. Supported by NASA NNJ04HF72G