Mixed muscle protein synthesis and breakdown after resistance exercise in humans.
Level 3 - non-randomized controlled study
Small repeated-measures physiological study without reported randomization
PubMed 9252485 · doi:10.1152/ajpendo.1997.273.1.E99
What was done
Eight untrained volunteers (4 males, 4 females) performed a single bout of resistance exercise (eight sets of eight repetitions at 80% 1RM) consisting of either concentric or eccentric contractions. Mixed muscle protein fractional synthesis rate (FSR) and fractional breakdown rate (FBR) were measured using primed constant infusions of [2H5]phenylalanine and 15N-phenylalanine. Subjects were tested in the fasted state across four sessions: at rest, and at 3, 24, and 48 hours post-exercise.
What was found
No significant differences were observed between concentric and eccentric exercise for FSR, FBR, or net balance (FSR minus FBR). Exercise increased muscle FSR relative to rest by 112% at 3 h, 65% at 24 h, and 34% at 48 h (all P < 0.01). Muscle FBR was elevated by 31% at 3 h and 18% at 24 h (both P < 0.05), returning to baseline by 48 h. Net balance improved from rest (-0.0573 ± 0.003 %/h) at 3 h (-0.0298 ± 0.003 %/h), 24 h (-0.0413 ± 0.004 %/h), and 48 h (-0.0440 ± 0.005 %/h), remaining significantly negative across all time points (P < 0.05). FSR and FBR were strongly correlated (r = 0.88, P < 0.001).
Why it matters
The study shows that a single session of resistance exercise stimulates elevated muscle protein turnover and improves net protein balance for up to two days, irrespective of whether concentric or eccentric actions are performed.
Limits
The sample size was very small (8 subjects total). The trial was conducted entirely in the fasted state, meaning net balance remained negative and the interactive effects of feeding and exercise were not evaluated.
Cited by
- supports Muscle protein synthesis remains elevated for up to 48 hours following exercise.