Some guys have been saying that it’s a god idea to tailor your rep ranges to the fiber make-up of the muscle you’re using.
For example, hamstrings are fast-twitch-dominant, so use low reps and heavy load for glute-ham raises and RDL’s. Calves are slow-twitch-dominant, so use high reps for calf raises. Quads are in-between, so use moderate reps for squats.
However, if I understand correctly, don’t slow twitch muscles have ZERO ability to hypertrophy? Slow twitch muscles are the ones used by marathon runners, who take high-rep work to the extreme, and they don’t tend to be jacked. It should follow that using high rep work should lead to zero hypertrophy gain since slow twitch muscle fibers cannot grow no matter how hard they are worked, but obviously that isn’t the case because high rep squats are effective for hypertrophy.
Furthermore, if you got a guy like Usain Bolt (who must be VERY fast-twitch dominant) to do 20-rep squats, would you predict he wouldn’t get much growth from it?