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TRANSLATIONAL PHYSIOLOGY

ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

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-d₅]phenylalanine, L-[ring-¹³C₆]phenylalanine, and d₃--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

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