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.

Regulation of muscle protein metabolism by nutrition and exercise

“…A study comparing the effects of 10 weeks of resistance training (3-times per week, 3 sets of leg extension until fatigue failure) performed at 30% 1RM and 80% 1RM also supports the results of other studies comparing exercise volume and fatigue 22) . Moreover, muscle hypertrophy was observed in resistance training performed to fatigue failure independently of exercise intensity in well- trained subjects 23) .…”

Physiological stimuli necessary for muscle hypertrophy

“…These results were in agreement with the aforementioned studies of signal pathways, suggesting the importance of total exercise volume and metabolic stress for muscle hypertrophy. However, it should be noted that strength gain (1RM strength) was greater for the higher exercise loads in these studies 2,30) , implying that low-load exercise cannot completely replace high-load exercise. Importantly, these studies were conducted on untrained or recreationally active adults, with the training period being less than 3 months.…”

“…A study by Mitchell et al (2012) investigated the effects of low-and high-load training on muscle hypertrophy, using the following 3 groups: 3 sets × 30% 1RM to failure, 3 sets × 80% 1RM to failure, and 1 set × 80% 1RM to failure 2) . The changes in muscle size and strength were evaluated after a 10-week training, consisting of 3 sessions per week.…”

“…However, recent research has shown that, when each exercise set is performed until volitional failure, low-load resistance exercise can induce comparable hypertrophy to that of high-load resistance exercise at the whole muscle or myofiber level 2,3) . At lifting failure, the degree of fatigue or metabolic stress may be greater for low-load exercise, given that one cannot continue lifting repetitions even with light weights.…”

Cycle training induces muscle hypertrophy and strength gain: strategies and mechanisms

“…However, in recent years, it has been established that, when performed repetitively or until volitional failure, a low exercise intensity such as 30% 1RM can lead to an increase in myofibrillar protein synthesis (9). These results suggest that high external loads are not a prerequisite for increasing muscle protein synthesis or muscle size (60). Peak muscular activation in VL and vastus medialis (VM) during cycling corresponded to approximately 50% of maximum voluntary contraction (MVC) (19).…”