Johnsson, K. A.; Freitas, E. D.; Roust, L. R.; De Filippis, E.; Gu, H.; Buras, M.; Katsanos, C. S.

Obesity alters protein metabolism in skeletal muscle, and although exercise and amino acids act synergistically to regulate muscle anabolism in healthy humans, this interaction may be impaired in obesity. We examined whether acute aerobic exercise alters amino acid-stimulated muscle protein synthesis during the immediate postexercise period in subjects with obesity. Sixteen sedentary adults with a body mass index >30 kg/m2 underwent stable-isotope tracer infusion studies to determine mixed-muscle fractional synthesis rate (FSR) in the basal (fasted) state and under two experimental conditions: eight subjects received an amino acid infusion (AA), while another eight performed 45 min of cycling at ~65% heart rate reserve immediately prior to the amino acid infusion (EX+AA). Amino acid infusion significantly increased muscle protein FSR in AA (P < 0.0001). In contrast, no significant increase was observed in EX+AA (P > 0.05), and the amino acid-stimulated increase in muscle protein FSR in EX+AA was 78% lower than that in the AA (P < 0.01). Amino acid infusion increased plasma amino acid concentrations in both conditions (P < 0.05); however, plasma concentrations of essential and branched-chain amino acids, including leucine, were lower in the EX+AA condition (P < 0.05). Changes in muscle protein FSR were positively associated with plasma leucine concentrations during the amino acid infusion (P < 0.05). These findings suggest that, in humans with obesity, aerobic exercise may abolish amino acid-stimulated muscle protein synthesis during the immediate postexercise period, with implications when considering nutritional strategies designed to optimize muscle anabolism in this population.