Both research and decades of anecdotal reports from bodybuilders confirm that rep ranges of 8–12 are best for building muscle and reps of 6 or less are best for building strength. Most of the bodybuilders featured in FLEX perform sets in the 8–12 range or even higher. Yet there still is a debate in many gyms about whether heavy weight and low reps is the best scheme for building muscle.
Research from Finland and the United States shows further support for higher reps. In the study, subjects performed a leg workout doing either 5 sets of 10 reps or 15 sets of 1 rep, then researchers took a muscle sample from the subjects’ quads to analyze the muscle for biochemical factors that instigate muscle growth. They specifically were looking at mitogen-activated protein kinase signaling pathways. They reported that only when the subjects did 5 sets of 10 reps was there an increase in MAPK signaling, which could instigate muscle growth. So focus on using reps in the 8–12 rep range, but as we always tell you, mix it up by going heavier in some workouts and lighter in others.