Muscle protein turnover following resistance exercise

The fractional synthetic rate (FSR) and fractional breakdown rate (FBR) of mixed skeletal muscle protein were determined, using primed constant infusions of d₅-phenylalanine and ¹⁵N-phenylalanine respectively, prior to and following an isolated bout of resistance exercise. Subjects were 8 healthy volunteers (4 male, 4 female, age=21± lyr; mean±SE) who were studied at: rest, and at 3h, 24h, and 48h post-exercise, in the fasted condition. Exercise resulted in a 112% increase in FSR, above rest (P<0.05), at 3h post-exercise. In addition, FSR remained elevated by 65% and 34% at 24h and 48h, respectively (P<0.05). Exercise also resulted in elevations in FBR: 3h=31%, and 24h=18% (P<0.05). However, FBR was at resting levels by 48h Net muscle protein balance (FSR - FBR) was higher than rest at all times studied, but was highest at 3h post-exercise (rest=-0.0573±0.003; 3h=-0.0298±0.003; 24h=-0.0413±0.004; 48h=-0.0440±0.005; all %/h; P<0.01) Muscle protein net balance was always significantly less than zero, however. There was also a significant correlation between FSR and FBR (r=0.88; P<0.001). These results indicate that a single bout of weightlifting results in a stimulation of both FSR and FBR, but that FSR remains elevated for longer than FBR These results clearly demonstrate that exercise results in an increased protein balance within muscle, up to 48h post-exercise.