The purpose of this investigation was to assess mixed muscle protein synthesis (FSR) and the expression of genes involved in skeletal muscle remodeling after aerobic exercise in the fasted and fed states. Eight recreationally active males (25±1y; VO2max: 52±2 ml⋅kg-1⋅min-1) performed 60-min of cycle ergometry at 72±1% VO2max on two occasions in a counter-balanced design. Subjects ingested a non-caloric placebo (EX-FAST) or a beverage containing (per kg body weight): 5kcal, 0.83g carbohydrate, 0.37g protein and 0.03g fat (EX-FED) immediately and 1h after exercise. FSR was assessed at rest and following exercise with the use of a L-[ring 2H5]-phenylalanine infusion combined with muscle biopsies at 2 and 6h post-exercise. mRNA expression was assessed at 2 and 6h post-exercise via real-time RT-PCR. FSR was higher (P<0.05) after exercise in both EX-FAST (0.112 ± 0.010%·h-1) and EX-FED (0.129 ± 0.014 %·h-1) compared to rest (0.071 ± 0.005 %·h-1). Feeding attenuated (P<0.05) the mRNA expression of proteolytic factors MuRF-1 (6h) and calpain-2 (2 and 6h) post-exercise but did not alter FOXO3A, calpain-1, caspase3, or myostatin mRNA expression compared to EX-FAST. Myogenic regulatory factor (MRF4) mRNA was also attenuated (P<0.05) at 2 and 6h post-exercise in EX-FED compared to EX-FAST. These data demonstrate that a non-exhaustive bout of aerobic exercise stimulates skeletal muscle FSR in the fasted state and that feeding does not measurably enhance FSR between 2 and 6h after aerobic exercise. Additionally, post-exercise nutrient intake attenuates the expression of factors involved in the ubiquitin-proteosome and Ca++ dependent protein degradation pathways. These data provide insight into the role of feeding on muscle protein metabolism during recovery from aerobic exercise.
- protein turnover
- Copyright © 2010, American Journal of Physiology - Regulatory, Integrative and Comparative Physiology