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

Exercise Metabolism Research Group, McMaster University, Hamilton, Ontario, Canada Submitted 4 September 2007 ; accepted in final form 9 November 2007 ABSTRACT 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-d 5 ]phenylalanine, L -[ring- 13 C 6 ]phenylalanine, and d 3 - -ketoisocaproic 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 4 h (T: 162 ± 76%; UT: 108 ± 62%, P < 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. hypertrophy; feeding; weight lifting Address for reprint requests and other correspondence: S. M. Phillips, Exercise Metabolism research Group, Dept. of Kinesiology, McMaster Univ., 1280 Main St. West, Hamilton, ON L8S 4K1 (e-mail: phillis{at}mcmaster.ca )