Mitchell C., Churchward-Venne T., West D., et al (2012). Resistance exercise load does not determine training-mediated hypertrophic gains in young men. Journal of Applied Physiology, 113:71-77 Details
Customer study highlights
Improving one's physical prowess by building muscle mass and strength requires a great deal of hard work, usually by following a prescribed combination of repetitions for a given resistance load. For example, in his latest book "The Encyclopedia of Modern Bodybuilding", Arnold Schwarzenegger advocates for the use of 8-12 repetitions for the upper body and 12-16 for the lower body.
Yet researchers from McMaster University in Canada think it's time to say "hasta la vista, baby" to this view. In their study, Mitchell et al tested for post-exercise muscle protein synthesis rates in 18 healthy young men subjected to 10 weeks of one of three possible unilateral leg extension conditions: 80% maximal load, single set; 80% maximal load, 3 sets; and 30% maximal load, 3 sets. Subjects consumed identical protein supplements immediately after training. Muscle volume was measured before and after the experiment using magnetic resonance imaging. Muscle function was assessed using analogue torque signals from a dynamometer sampled with a PowerLab. To measure protein synthesis and muscle fiber cross sectional area, muscle biopsies were taken for biochemical analysis.
After 10 weeks of training the researchers found that subjects' quadriceps muscle volume had increased by 4-7% and maximal voluntary isometric contraction force had increased by 27-35%. Consistent with hypertrophy, both type I and II muscle fiber areas were increased with training. None of these changes were significantly influenced by training condition, however. Similarly, when the researchers examined muscle biopsies of the vastus lateralis 1 hour after the initial resistance exercise, changes in specific signaling protein levels (e.g., mTOR) were elevated, irrespective of the training condition.
While the authors aren't suggesting that Arnie's book needs to be terminated, their results do make a case for suggesting that there is more flexibility in hypertrophy-specific repetition load ranges than commonly advocated.