Effective RepsReps × RIR → stimulus, per muscle

What an effective rep is

Muscle grows from reps done while nearly all of its fibers are working. On a normal set that happens in roughly the last 5 reps before failure. So a set of 10 at RIR 0 scores 5, the same set at RIR 2 scores 3, and at RIR 4 it scores 1.

How to log

• Pick the muscle, enter the reps you did, then tap RIR: how many more you could have done.
• RIR 5+ is logged but not counted. It's a warm-up, not a working set.
• Be honest with RIR. Most people think they're closer to failure than they really are.

Rest-pause sets

Turn on Rest-pause and enter two numbers: the activation set (taken close to failure) and the total reps of the mini-sets after it. The activation set scores as normal. Every mini-set rep counts, because after short rests the muscle is already fully working. RIR is for the activation set. The whole thing counts as one working set.

The 20–40 target

20–40 effective reps per muscle per session is a practical working range taken from programs that are known to work. It hasn't been measured directly. Start at the low end. Going past 40 mostly adds fatigue.

Limits

• Heavy sets are undercounted. At about 80% of your max (a 5–8 rep weight), every rep counts, even well short of failure. The tool doesn't know the load, so a heavy triple at RIR 3 shows 2 when it's really closer to 3.
• Weekly volume still matters. Aim for about 10–16 hard sets per muscle per week alongside the session numbers.
• Sets at RIR 3–4 still build muscle, just less per set.

The full reasoning is in the Hypertrophy Hub.