Submitted to: International Journal of Sport Nutrition and Exercise Metabolism
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2010
Publication Date: 8/20/2010
Citation: Pasiakos, S.M., Mcclung, H.L., Mcclung, J.P., Urso, M.L., Cloutier, G.J., Fielding, R.A. 2010. Molecular responses to moderate endurance exercise in skeletal muscle. International Journal of Sport Nutrition and Exercise Metabolism. 20(4):282-290. Interpretive Summary: This study was a collaboration between the JM USDA Human Nutrition Research Center on Aging and the US Army Research Institute of Environmental Medicine. In this study we examined how young soldiers responded to a single session of aerobic (endurance) exercise similar to riding a bicycle for one hour. We examined substances in the exercising muscles of these soldiers that control muscle growth and muscle breakdown. We found that following exercise some of the substances that control muscle breakdown were elevated. These data provide some insight into the molecular events associated with exercise in skeletal muscle and lay the foundation for future studies of nutritional modulators with exercise.
Technical Abstract: This study examined alterations in skeletal-muscle growth and atrophy-related molecular events after a single bout of moderate-intensity endurance exercise. Muscle biopsies were obtained from 10 men (23 +/- 1 yr, body mass 80 +/- 2 kg, and VO(2peak) 45 +/- 1 ml x kg'¹ x min'¹) immediately (0 hr) and 3 hr after a 60-min bout of cycle exercise (60% +/- 5% VO(2peak)). Corresponding muscle biopsies were also obtained under resting conditions. The phosphorylation status of insulin/IGF-PI3K molecular-signaling proteins, ubiquitin-proteasome-related gene expression, FOXO transcription factors, and myogenic regulatory factors in muscle samples was analyzed using multiplex analysis, Western blotting, and quantitative real-time polymerase chain reaction (qRT-PCR). A condition-time interaction was observed for Akt phosphorylation (p < .05) with multiplexing. Regardless of endurance exercise, Akt phosphorylation decreased and ERK phosphorylation increased at 3 hr compared with 0 hr (p < .05). Levels of p70(S6K)phosphorylation were 110% greater (p < .05) at 3 hr than at 0 hr using Western blots. MuRF mRNA expression postexercise increased; levels were 4.7- and 5.7-fold greater (p < .05) at 0 hr and 3 hr, respectively, than at rest with qRT-PCR. Atrogin mRNA expression was up-regulated 3.2-fold 3 hr postexercise compared with rest. These findings demonstrate modest changes in the molecular responses to moderate endurance exercise in the absence of nutrition. This study provides the groundwork for future investigations designed to optimize the metabolic conditions necessary to positively influence the cellular mechanisms specific to skeletal-muscle protein turnover during recovery from endurance exercise.