For as long as I’ve been lifting, I’ve heard the recommendation that 1-5 reps is for building strength, 8-12 reps is for increasing muscle size, and 15-20 reps is for increasing muscular endurance. Several variations on this theme exist.
The concepts of myofibrillar hypertrophy and sarcoplasmic hypertrophy, usually used to explain strength and size differences between strength athletes and bodybuilders, say that the heavier weights build actual contractile proteins in muscles (myofibrillar hypertrophy), and higher rep ranges (8-12) create more of a focus on increasing sarcoplasm, or the fluid, in muscles. Sarcoplasmic hypertrophy, however, is completely unsupported by any sort of scientific literature (unless Supertraining counts as scientific literature or you count transient increases in fluid as hypertrophy), and strength differences are much more easily explained through other ideas the evidence actually supports.
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Main Takeaways
-From the size principle, we know that sets must be high effort to recruit and fatigue all fibers. We don’t know the exact threshold for the effort needed to stimulate hypertrophy, and there are plenty of people who experience considerable muscle growth never lifting to failure, but generally it’s probably necessary to push sets within a few reps of failure.
-Rep range does not matter for hypertrophy (at least up to 30 reps/set for trained lifters and 100 reps/set for untrained old people), so long as the effort per set is equal. Muscles seem to grow the same whether you lift 3 reps to failure or 100 reps to failure. It remains to be seen whether muscles grow the same with something like 70% effort matched between groups rather than lifting to failure, but I believe they would.
-Strength increases are highly specific to the rep ranges used. If you want to get better at one-rep max attempts, you need to lift loads that are close to that. If you want to get better at high reps, you need to lift lighter loads. You can likely get better at both by doing both rep ranges. Think of the strength increases as studying specific material for an exam.
-Doing more sets or volume (it’s still a little unclear which better predicts gains, although I lean toward more sets) gives you more results.
