One of the hot debates in weight training circles centres on the notion of the optimal loads for eliciting maximal muscle recruitment. With the basic idea being to recruit as many motor units/muscle fibers as possible so as to maximally stimulate muscle hypertrophy.
While the traditional philosophy has been to lift heavy for maximum muscle recruitment, some researchers have recently put forward other theories proposing that maximal fiber recruitment occurs at the point of muscular failure somewhat independent of the number of repetitions.
While a couple of studies have already tested the relative effect of low versus high repetitions on muscle protein synthesis, these have been conducted on individuals who were not experienced in weight training and only used single-joint exercises to evaluate muscle recruitment. There in this study, researchers from Queen’s University in Canada, wanted to see if the same results could be produced in a group of experienced weight trainers using a range of multi-joint lower body exercises.
To test their model, the researchers took a group of 10 young resistance-trained men and had them perform sets of leg press at different intensities. The high load set was performed at 75% of 1-RM while the low-load set was performed at 30% of 1-RM. The sets were carried out to the point of momentary muscular failure, which was defined as the inability to perform another concentric action with proper form. Electromyography (EMG) activity of the exercising muscles were collected by means of multiple electrodes placed on the femoris, vastus lateralis, vastus medialis, and biceps femoris.
The results convincingly showed that EMG activity was significantly higher during the high load sets compared with low load (high rep). This was evidenced by significantly higher peak and mean EMG activity during the 75% 1-RM set versus 30% 1-RM set to failure. The authors were also able to show that training with a load of 30% 1-RM to momentary muscular failure did not maximally activate the full motor unit pool of major muscle groups like the quads.
This study seems to settle the question once and for all of whether high or low load sets are the best for muscle recruitment and resultant muscle hypertrophy. If your priority is muscle size, make sure you do your fair share of high load weight training.
Burd NA, et al. Bigger weights may not beget bigger muscles: evidence from acute muscle protein synthetic responses after resistance exercise. Appl Physiol Nutr Metab. 2012;37:551–554.