Muscle protein synthetic responses to exercise: effects of age, volume, and intensity.

We explored the relationships between resistance exercise volume/intensity and muscle myofibrillar protein synthetic (MPS) responses in young and older men. In a crossover design, four groups of six young (246 years) and older (705 years) men performed two volumes of resistance exercise: either 40% one repetition maximum (1RM) (3 14, then 6 14 repetitions) or 75% 1RM (3 8, then 6 8 repetitions), such that at the same volume, work was identical between intensities. Muscle biopsies were taken 0, 1, 2, and 4hours after exercise to measure MPS via myofibrillar bound [1,2-C-13(2)]leucine and indices of mammalian target of rapamycin signaling by immunoblotting. In younger men, doubling exercise volume produced limited added effects, whereas in older men, it resulted in greater MPS and p70S6 kinase (p70S6K(Thr389)) phosphorylation at both intensities, that is, MPS area under the curve: 75% (1 volume: 0.070.01 vs 2 volume: 0.14% 0.02% protein synthesized/4hours (p < .001). Doubling exercise volume is a valid strategy to maximize postexercise MPS in ageing.