Resistance training reduces the acute exercise-induced increase in muscle protein turnover

We examined the effect of resistance training on the response of mixed musc le protein fractional synthesis (FSR) and breakdown rates (FBR) by use of p rimed constant infusions of [H-2(5)]phenylalanine and [N-15]phenylalanine, respectively, to an isolated bout of pleiometric resistance exercise. Train ed subjects, who were performing regular resistance exercise (trained, T; n = 6), were compared with sedentary, untrained controls (untrained, UT; it = 6). The exercise test consisted of 10 sets (8 repetitions per set) of sin gle-leg knee flexion (i.e., pleiometric muscle contraction during lowering) at 120% of the subjects' predetermined single-leg 1 repetition maximum. Su bjects exercised one leg while their contralateral leg acted as a nonexerci sed (resting) control. Exercise resulted in an increase, above resting, in mixed muscle FSR in both groups (UT: rest, 0.036 +/- 0.002; exercise, 0.080 2 +/- 0.01; T: rest, 0.045 +/- 0.004; exercise, 0.067 +/- 0.01; all values in %/h; P < 0.01). In addition, exercise resulted in an increase in mixed m uscle FBR of 37 +/- 5% (rest, 0.076 +/- 0.005; exercise, 0.105 +/- 0.01; al l values in %/h; P < 0.01) in the UT group but did not significantly affect FBR in the T group. The resulting muscle net balance (FSR - FBR) was negat ive throughout the protocol (P < 0.05) but was increased in the exercised l eg in both groups (P < 0.05). We conclude that pleiometric muscle contracti ons induce an increase in mixed muscle protein synthetic rate within 4 h of completion of an exercise bout but that resistance training attenuates thi s increase. A single bout of pleiometric muscle contractions also increased the FBR of mixed muscle protein in UT but not in T subjects.