TIME COURSE OF MIXED MUSCLE PROTEIN SYNTHESIS FOLLOWING RESISTANCE EXERCISE IN HUMANS 1321

Abstract

The time course of changes in muscle protein synthetic rate following resistance exercise is unknown. In addition, the effect of contraction type(concentric or eccentric) on muscle protein synthesis is also unknown. Hence, the purposes of the current study were: 1) To examine the time course of muscle protein fractional synthetic rate (FSR); and 2) To determine the effect of contraction, eccentric or concentric on muscle FSR. FSR was determined in 8 untrained volunteers (4 male and 4 female; 22±2 yr; means±SD). Subjects were studied on 4 consecutive days: rest, and 3h, 24h, and 48h post-exercise. The exercise was 8 sets of 8 concentric or eccentric knee extension repetitions at 80% of the subject's 1 RM. Muscle FSR was determined using a primed constant infusion of d5-phenylalanine and the tracer incorporation, muscle biopsy (vastus lateralis) method. There was no effect of contraction mode on muscle protein FSR. Exercise resulted in a stimulation of FSR at 3h post-exercise to 112% greater than resting (rest = 0.055±0.016%/h, 3h = 0.118±0.027%/h; P<0.05). FSR fell(P<0.05) at 24h (0.092±0.024%/h) and 48h (0.075±0.022%/h), versus 3h, but remained elevated versus rest by 65% and 34%, respectively. There was no difference in FSR between 24 and 48h. These results suggest that exercise results in a stimulation of synthesis that peaks immediately following exercise, but is still elevated 48h after the initial stimulus. The stimulation of FSR by exercise is unaffected, however, by the type of muscular contraction performed during exercise.