Resistance exercise load does not determine training-mediated hypertrophic gains in young men
We have reported that the acute post-exercise increases in muscle protein synthesis rates, with differing nutritional support, are predictive of longer-term training-induced muscle hypertrophy. Here, we aimed to test whether the same was true with acute exercise-mediated changes in muscle protein synthesis. Eighteen men (21±1 yr, 22.6±2.1 kg∙m-2 means±SE) had their legs randomly assigned to two of three training conditions that differed in contraction intensity (% of maximal strength [1RM]) or contraction volume (1 or 3 sets of repetitions): 30%-3, 80%-1 and, 80%-3. Subjects trained each leg with their assigned regime for a period of 10wk, 3 times/wk. We made pre- and post-training measures of strength, muscle volume by magnetic resonance (MR) scans, as well as pre- and post-training biopsies of the vastus lateralis, and a single post-exercise (1h) biopsy following the first bout of exercise, to measure signalling proteins. Training-induced increases in MR-measured muscle volume were significant (P<0.01), with no difference between groups: 30%-3 = 6.8±1.8%, 80%-1 = 3.2±0.8%, and 80%-3= 7.2±1.9%, P=0.18. Isotonic maximal strength gains were not different between 80%-1 and 80%-3, but were greater than 30% -3 (P=0.04), whereas training-induced isometric strength gains were significant but not different between conditions (P =0.92). Biopsies taken 1h following the initial resistance exercise bout showed increased phosphorylation (P<0.05) of p70S6K only in the 80%-1 and 80%-3 conditions. There was no correlation between phosphorylation of any signalling protein and hypertrophy. In accordance with our previous acute measurements of muscle protein synthetic rates a lower load lifted to failure resulted in similar hypertrophy as a heavy load lifted to failure.