Abstract
The purpose of this study was to determine whether the training responses observed with low-load resistance exercise to volitional fatigue translates into significant muscle hypertrophy, and compare that response to high-load resistance training. Nine previously untrained men (aged 25 [SD 3] years at the beginning of the study, standing height 1.73 [SD 0.07] m, body mass 68.9 [SD 8.1] kg) completed 6-week of high load-resistance training (HL-RT) (75% of one repeti-tion maximal [1RM], 3-sets, 3x/wk) followed by 12 months of detraining. Following this, subjects completed 6 weeks of low load-resistance training (LL-RT) to volitional fatigue (30% 1 RM, 4 sets, 3x/wk). Increases (p 0.05) in magnetic resonance imaging-measured triceps brachii and pectorals major muscle cross-sectional areas were similar for both HL-RT (11.9% and 17.6%, respectively) and LL-RT (9.8% and 21.1%, respectively). In addition, both groups increased (p 0.05) 1RM and maximal elbow extension strength following training; however, the percent increases in 1RM (8.6% vs. 21.0%) and elbow extension strength (6.5% vs. 13.9%) were significantly (p 0.05) lower with LL-RT. Both protocols elicited similar increases in muscle cross-sectional area, however differences were observed in strength. An explanation of the smaller relative increases in strength may be due to the fact that detraining after HL-RT did not cause strength values to return to baseline levels thereby producing smaller changes in strength. In addition, the results may also suggest that the consistent practice of lifting a heavy load is necessary to maximize gains in muscular strength of the trained movement. These results demonstrate that significant muscle hypertrophy can occur without high-load resistance training and suggests that the focus on percentage of external load as the important deciding factor on muscle hypertrophy is too simplistic and inappropriate.
Highlights
As a muscle is overloaded from increased mechanical work, the added stress increases skeletal muscle amino acid transporter expression [1], which in turn enhances the synthesis of the contractile proteins, actin and myosin [2]
The purpose of this study was to determine whether the training responses observed with low-load resistance exercise to volitional fatigue translates into significant muscle hypertrophy, and compare that response to high-load resistance training
These results demonstrate that significant muscle hypertrophy can occur without high-load resistance training and suggests that the focus on percentage of external load as the important deciding factor on muscle hypertrophy is too simplistic and inappropriate
Summary
As a muscle is overloaded from increased mechanical work, the added stress increases skeletal muscle amino acid transporter expression [1], which in turn enhances the synthesis of the contractile proteins, actin and myosin [2] These acute positive balances between muscle protein synthesis (MPS) and muscle protein breakdown (MPB) lead to skeletal muscle hypertrophy over time which occurs from both an increase in the thickness and number of myofibrils [see molecular pathway review by Adams [3]. To illustrate, when four sets of resistance exercise was performed at 30% 1 RM to volitional fatigue, myofibril MPS was elevated to the same level as 90% 1 RM to volitional fatigue (not work matched) [8] This is contrary to what has commonly been reported in the literature which states that training to volitional fatigue is not an effective stimulus unless a sufficient external load as defined by percentage of 1 RM (~80% 1 RM) is lifted. The common thought has always been that higher repetition training
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