5 to 30 Reps.
The Range Is Wide. The Rule Is Narrow.

Eight to twelve reps for size. Three to five for strength. Fifteen plus for "toning". The rep continuum is one of the oldest ideas in the gym and the research of the last decade has quietly taken it apart.

The range is wide

A meta-analysis of 21 studies where every set went to failure found no meaningful difference in muscle growth between loads under 60% of max and loads over it. The effect size was 0.03, which is nothing.^[1] In trained men, 20 to 25 reps grew muscle as well as 8 to 12.^[2][3] Pull the results together and the range where muscle grows runs from roughly five reps to roughly thirty, as long as the sets are taken close to failure.^[4]

I've written before about why 8 to 12 isn't magic. This is the other half: what the range is for, and what it isn't.

Heavy loads do win one thing: strength. If you want a bigger one-rep max, train heavy. For size, the rep count is close to irrelevant.

The rule is narrow

"As long as the sets are taken close to failure" is doing all the work in that sentence. A set of 25 at three reps from failure and a set of 25 that stops when it feels like a lot are not the same set, and only one of them grows anything. A meta-analysis of proximity to failure found a small but consistent edge for sets taken closer to it.^[5] The rep range buys you freedom. Effort is the thing you can't trade away.

Anywhere from 5 to 30 reps builds muscle. Stopping short of failure doesn't, at any rep count.

So why not do everything heavy

Because at some exercises the rep count changes which muscle does the work. A heavy lateral raise stops being a side-delt exercise around rep six: the traps take over, the torso swings, and you've built a shrug. A heavy dumbbell curl becomes a hip hinge. Small, single-joint movements need enough reps that the load stays light enough for the target muscle to be the thing that fails. That's a form argument, not a growth argument, and it's why isolation work sits at 10 to 15 reps while squats and presses can run at 5 to 10.

The other direction is fatigue. Thirty-rep squats grow quads about as well as eight-rep squats, but they're brutal, they take longer, and most people won't keep doing them. Moderate loads are the default because they're the easiest place to actually get close to failure, not because they're magic.

What the app does

Coast assigns rep ranges by what the exercise is, not by what the goal is called. Compounds sit at 5 to 10, isolation at 10 to 15, and the reps climb from the bottom of the band at a held load so progression is visible. Every set carries a target for how close to failure it should be, which changes week to week. The band is the freedom. The failure target is the rule.