And then along came Brad Schoenfeld and Co., who laid hands upon the bros and dudes of the land, and yea Brad said unto them: “My fellas; my champs; my guys. Lay down your swords, for it is not the number of reps that matter. Thou must use sufficiently heavy weights, at least 30 percent of thy one-rep max, and thou mayest not cast the weights down until thou hast completed enough reps that thy muscles ache with exertion and cry out for relief. It is then and only then that thy muscle tissues shall be sufficiently shredded as to produce hypertrophy.” And Brad withdrew his hands, and it was so.[^1]
What was the specific, scientific finding? In 2021, Schoenfeld published a study that broke down how muscles can be trained in basically three dimensions, three different ways:
Strength: <6 reps for probably > RPE 7. Building muscle strength has the most specific rep needs (sets of fewer than 5, for weights that are at least a 7/10 or so on the effort scale).
Endurance: pretty much whatever till you are tired. Building muscle endurance will happen from doing pretty much anything until your muscle gets tired, and then doing it for a little longer than that.
Size: At least 30% of 1RM weight, for as many reps as needed to get near failure with that weight (probably RPE 8 or more). Building muscle size happens when you use decently heavy weights (at least 30% of your one-rep max) but less weight than would put you in the “strength” range, to the point of failure or near-failure (an 8-10/10 on the effort scale).