Resistance exercise load does not determine training-mediated hypertrophic gains in young men

Abstract

We have reported that the acute postexercise 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 (1 repetition maximum)] 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 10 wk, 3 times/wk. We made pre- and posttraining measures of strength, muscle volume by magnetic resonance (MR) scans, as well as pre- and posttraining biopsies of the vastus lateralis, and a single postexercise (1 h) biopsy following the first bout of exercise, to measure signaling 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 1 h 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 signaling 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.

Fig. 1.

Percentage change in quadriceps muscle volume following 10 wk of resistance training. The 3 training condition groups differed in contraction intensity [% of maximal strength (1 repetition maximum)] or contraction volume (1 or 3 sets of repetitions): 30%-3, 80%-1, and 80%-3. There was a significant main effect for time (increase in quadriceps volume pre- to posttraining, P < 0.0001). N = 12 legs in each condition.

Fig. 2.

Phosphorylated Akt, mammalian target of rapamycin (mTOR), and P70S6K at rest and 1 h following resistance exercise. A: Akt phosphorylated at Ser 473 expressed relative to total Akt. There are no significant differences between conditions. B: mTOR phosphorylated at Ser 2448 relative to total mTOR. *Main effect for greater phosphorylated mTOR 1 h following resistance exercise (P < 0.05). C: p70S6K phosphorylated at Thr 389 relative to total p70S6K. *Significant increases in phosphorylated p70S6K 1 h after 1 or 3 sets at 80% of one repetition maximum (1RM) but not 3 sets at 30% of 1RM (P < 0.05). D: correlation between p70S6K phosphorylation and muscle hypertrophy, r = −0.03 (P = 0.88). N = 12 legs in each condition.

Fig. 3.

Knee extension strength. A: the maximal load that could be lifted prior to training and after 10 wk of training. *Significantly greater than prior to training (P < 0.05). †Significantly greater than the 3-sets at 30% of 1RM condition. B: single leg isometric knee extension torque before and after 10 wk of training. *Significantly greater than prior to training (P < 0.05). N = 12 legs in each condition.

Fig. 4.

Maximal work and repetitions with 30 and 80% of 1RM before and after 10 wk of resistance training. Load product (in arbitrary units) is the product of load in kg and repetitions completed. A: work completed at 80% of the subject's 1RM (determined within 1 wk of the test). *Significant main effect for an increase in work performed with 80% of 1RM pre- to posttraining (P < 0.05). †Significantly less work at 80% 1RM after training in the 3-sets at 30% of 1RM condition than the other two groups (P < 0.05). B: work completed with 30% of the subject's 1RM. *Significant main effect for an increase in work performed with 30% of 1RM pre- to posttraining (P < 0.05). C: maximal number of repetitions completed with 80% of 1RM (determined within 1 wk of the test). *Significant main effect for an increase in the number of repetitions performed with 80% of 1RM pre- to posttraining (P < 0.05). D: maximal number of repetitions completed with 30% of 1RM. *3-sets at 30% of 1RM condition completed more repetitions after training than before (P < 0.05). †3-sets at 30% of 1RM condition completed more repetitions after training than either of the other groups. N = 12 legs in each condition.