Enhanced rates of muscle protein synthesis and elevated mTOR signalling following endurance exercise in human subjects

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Abstract
The major aim of this study was to determine the fractional rate of protein synthesis (FSR) during the early period of recovery after intensive aerobic exercise in the absence of nutritional supplementation. Sixteen male subjects performed one-legged cycling exercise for 1 h at approx. 65-70% of their one-legged maximal oxygen uptake. Using the stable isotope technique, the FSR in the vastus lateralis of both legs were determined during two periods, 0-90 min (n = 8) and 90-180 min (n = 8) after exercise. Biopsies were taken from both exercising and resting muscle before exercise, immediately after and following 90 or 180 min of recovery. During the initial 90 min of recovery, FSR in the exercising muscle tended to be higher than in the resting muscle (1.57 ± 0.12 vs. 1.44 ± 0.07% 24 h(-1); P = 0.1) and was significantly higher during the period 90-180 min after exercise (1.74 ± 0.14 vs. 1.43 ± 0.12% 24 h(-1) ; P < 0.05). Exercise induced a 60% increase (P < 0.05) in phosphorylation of mTOR and a fivefold increase (P < 0.05) in Thr(389) phosphorylation of p70S6 kinase as well as a 30% reduction (P < 0.05) in phosphorylation of eEF2. Phosphorylation of AMP-activated protein kinase was enhanced by 40% (P < 0.05) after exercise, but no significant effect on phosphorylation of Akt, or eIF2Bε was observed immediately after exercise. These findings indicate that during the first 3 h of recovery after intensive endurance exercise FSR gradually increases. Moreover, a stimulation of the mTOR-signalling pathway may be at least partially responsible for this elevated protein synthesis.

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