Molecular adaptations to aerobic exercise training in skeletal muscle of older women

Background. We have recently shown that 12 weeks of progressive aerobic exercise training improves whole-muscle size and function in older women. The purpose of this investigation was to evaluate molecular markers that may be associated with muscle hypertrophy after aerobic training in aging skeletal muscle. Methods. Muscle biopsies were obtained before and after 12 weeks of aerobic exercise training on a cycle ergometer in nine older women (70 ± 2 years) to determine basal levels of messenger RNA and protein content of select myogenic, proteolytic, and mitochondrial factors. Results. The training program increased (p <. 05) aerobic capacity 30 ± 9%, whole-muscle cross-sectional area 11 ± 2%, and whole-muscle force production 29 ± 8%. Basal messenger RNA levels of FOXO3A, myostatin, HSP70, and MRF4 were lower (p <. 05) after aerobic training. FOXO3A, FOXO3A phosphorylation, and HSP70 protein content were unaltered after training. Mitochondrial protein COX IV was elevated (p <. 05) 33 ± 7% after aerobic training, whereas PGC-1α protein content was 20 ± 5% lower (p <. 05). Conclusions. These data suggest that reductions in FOXO3A and myostatin messenger RNA are potentially associated with exercise-induced muscle hypertrophy. Additionally, it appears that mitochondrial biogenesis can occur with aerobic training in older women independent of increased PGC-1α protein. Aerobic exercise training alters molecular factors related to the regulation of skeletal muscle, which supports the beneficial role of aerobic training for improving muscle health in older women.