How long should you rest between sets?

Two to five minutes between heavy compound sets — squats, deadlifts, presses — and one to two minutes for lighter or single-joint work. The longer rests are not a luxury: a 2016 study by Brad Schoenfeld and colleagues in the Journal of Strength and Conditioning Research found that trained men resting three minutes gained more strength and more muscle over eight weeks than those resting one, on the same programme, because the extra rest let them keep the reps up across sets. Rest is what makes the next set count.

Longer still — up to five minutes — for a heavy single or triple, where it is the nervous system rather than the muscle that needs the time. The common error is the opposite of laziness: cutting rest to feel productive, and losing a rep a set for it.

How does Liftor decide the rest?

From the exercise, then from the day. The base is two minutes for a heavy compound, ninety seconds for a lighter compound, a minute for an isolation exercise, forty-five seconds between conditioning intervals and twenty during warm-ups. Then the modifiers: thirty seconds more for a low-rep strength set; fifteen more when the load is 85% or above of your best on that lift; fifteen fewer on a recovery or deload day; more again if you had a drink the night before, because recovery the morning after is measurably worse. Set your own preferred base and the modifiers still apply on top of it.

Why should the rest timer start itself?

Because the set you just finished is the moment you are least likely to tap a button. Liftor starts the countdown when the set is logged and shows the reason for the length — “heavy compound, 2:00 base, +15 s at 85%” — so the number is an instruction you can read rather than a rule you have to trust. Skip it when you need to. The next one starts itself as well.

Is shorter rest better for muscle growth?

No, and the idea that it was came from a plausible mechanism rather than a result. Short rests raise the burn and the pump, and for years that metabolic stress was assumed to build more muscle. When Schoenfeld and colleagues tested it directly in 2016 — trained men, the same programme, one minute against three — the three-minute group gained more strength and more muscle, because they kept their reps up across the sets. Grgic and colleagues then reviewed twenty-three studies and 491 people in 2018 and drew the line at two minutes: rest longer than that to maximise strength if you are trained, while sixty to 120 seconds is enough for beginners, and short rests still produce gains for everyone.

The variable that matters is the work you can still do in set three. A rest that lets you repeat the reps is long enough; one that costs a rep a set is not, however productive it feels. Liftor’s bases are set on that principle and its modifiers lengthen them when the set is heavy or low-rep, which is exactly when the third set is most at risk.

How long to rest for strength, size and endurance?

The set	Rest	Why
Heavy compound, 1–5 reps	3–5 min	The nervous system is what needs the time
Compound, 6–12 reps	2–3 min	Keeps the reps up across sets, which is what grows muscle
Isolation, 8–15 reps	1–2 min	Small muscles recover fast; the joints are not loaded
Conditioning intervals	30–60 s	The incomplete rest is the training
Warm-up sets	20–30 s	Nothing to recover from yet

Liftor’s bases sit inside those bands — 120 seconds for a heavy compound, 90 for a lighter one, 60 for isolation work, 45 between conditioning intervals, 20 in warm-ups — and the modifiers move them toward the top of the band when the set is a low-rep strength set or the load is 85% or more of your best. The bases are deliberately at the shorter end, because the modifiers only ever add for the sets that need it.

How long should you rest in a superset?

Long enough for the muscle that is about to work, which has usually been resting while the other one worked. Pairing opposing movements — a row with a press, a curl with an extension — lets one recover during the other, so thirty to sixty seconds between the two exercises and a full rest after the pair keeps the quality of both. Pairing two exercises for the same muscle is a different tool: that is a drop in load disguised as efficiency, and it belongs at the end of a session, not the start.

The app times what it prescribes. A conditioning pair runs on the 45-second base; a strength pair keeps each lift’s own rest, because a superset of two heavy compounds is two heavy compounds. The timer starts when the set is logged either way, and the reason for its length is printed under the number.

Sources

Schoenfeld BJ et al. Longer interset rest periods enhance muscle strength and hypertrophy in resistance-trained men. Journal of Strength and Conditioning Research, 2016; 30(7): 1805–1812
Grgic J, Schoenfeld BJ, Skrepnik M, Davies TB, Mikulic P. Effects of rest interval duration in resistance training on measures of muscular strength: a systematic review. Sports Medicine, 2018; 48(1): 137–151
Liftor’s rest timer: the five bases and the modifiers (utils/smartRestTimer.ts in the app’s source)