“Your muscles can’t count.” Many pro bodybuilders have uttered that statement to me in interviews over the years in response to my question on how many reps they tend to do per set. The thing is, they explain, there is no magic number of reps that equates to maximizing muscle growth.
Just like you, they’ve heard the recommendations over the years and seen the studies pegging the “ideal” reps per set for bodybuilders at anywhere from eight to 12. Any fewer, it’s argued, and you’re not stimulating enough muscle fibers, while any more and you’re training more for endurance than pure size.
The reality, however, is much less cut-and-dried, leading to that common refrain from the pros. Your muscles, indeed, can’t count—a muscle fiber has no programming within it to automatically respond to a certain number of times it contracts. It isn’t miraculously prompted to grow when exposed to eight reps. Or 10. Or 20. Nope, the actions that induce muscle breakdown and thus the internal chemical reactions that release hormones for repair and regeneration are much more fluid.
Sometimes, perhaps just three or four reps could do the trick. Other times, it can be that oft-cited 10. But in any case, you need to go until you reach the threshold where you prompt the chemical reactions that promote growth. It’s about pushing your muscles a little further than they can normally handle, requiring them to respond and adapt. That, in turn, relies more on “time under tension”—the amount of time your muscle is under stress during a set—than any particular number of reps.