Resistance training alters the response of fed state mixed muscle protein synthesis in young men

摘要

First published November 21, 2007; doi:10.1152/ajpregu.00636.2007.-Ten healthy young men (21.0 +-1.5 yr, 1.79 +- 0.1 m, 82.7 +- 14.7 kg, means +- SD) participated in 8 wk of intense unilateral resistance training (knee extension exercise) such that one leg was trained (T) and the other acted as an untrained (UT) control. After the 8 wk of unilateral training, infusions of L-[ring-d5]phenylalanine, L-[ring-I3C6]phenylalanine, and d3-a-ke-toisocaproic acid were used to measure mixed muscle protein synthesis in the T and UT legs by the direct incorporation method [fractional synthetic rate (FSR)]. Protein synthesis was determined at rest as well as 4 h and 28 h after an acute bout of resistance exercise performed at the same intensity relative to the gain in single repetition maximum before and after training. Training increased mean muscle fiber cross-sectional area only in the T leg (type I: 16 +- 10%; type II: 20 +-19%, P < 0.05). Acute resistance exercise increased muscle protein FSR in both legs at 4h (T: 162 +- 76%; UT: 108 +- 62%, F < 0.01 vs. rest) with the increase in the T leg being significantly higher than in the UT leg at this time (P < 0.01). At 28 h postexercise, FSR in the T leg had returned to resting levels; however, the rate of protein synthesis in the UT leg remained elevated above resting (70 +- 49%, P < 0.01). We conclude that resistance training attenuates the protein synthetic response to acute resistance exercise, despite higher initial increases in FSR, by shortening the duration for which protein synthesis is elevated.