Reps starts a countdown the moment you check off a set. Three minutes after a compound lift, 90 seconds after an isolation lift, 60 seconds after a bodyweight set. If the set carries its own rest value from a program, that always wins.
Those three numbers are defaults, not doctrine. Here is where they come from and when to ignore them.
Why three minutes on compounds
A heavy set of five is powered mostly by stored phosphocreatine, and refilling that store takes minutes, not seconds. Harris and colleagues measured the time course directly in human quadriceps and found recovery happens in two phases: a fast one with a half-time of 21 to 22 seconds, and a slow one with a half-time above 170 seconds.
Read that second number again. A half-time of nearly three minutes means the slow phase is still only halfway done at the three-minute mark. Rest is not a switch that flips at some magic duration; it's a curve you can stop climbing whenever you decide the next set matters less.
Cut rest to a minute and the next set starts on a partly empty tank. You will feel that as fewer reps at the same weight, which is exactly the signal double progression reads. Short rest doesn't just cost you that set; it feeds bad data to whatever decides your next session.
The training outcome follows the physiology. Schoenfeld and colleagues took 21 resistance-trained men through 8 weeks of identical programming and varied one thing: one minute of rest versus three. The three-minute group finished with significantly greater 1RM squat and bench press, and significantly greater muscle thickness in the anterior thigh. Triceps thickness leaned the same way without reaching significance.
That result cut against a long-standing assumption that short rest builds more muscle by driving more metabolic stress. It doesn't, once the volume you can actually complete starts dropping with it.
Three minutes is the honest default for a set that taxes multiple joints and a lot of muscle: squat, bench, deadlift, row, overhead press, weighted pull-up.
Why 90 seconds on isolation
A set of curls uses less muscle mass and produces less systemic fatigue, so the recovery bill is smaller. Sahlin's work on energy supply and fatigue makes the mechanism plain: the deeper the metabolic disturbance, the longer the recovery, and a single-joint set on a small muscle simply doesn't disturb that much.
Ninety seconds is enough for the next set of curls, lateral raises, or triceps extensions to be honest work rather than a fumble.
Why 60 seconds on bodyweight
Unloaded sets (push-ups, air squats, planks, most core work) recover fastest. A minute is enough to keep the reps real without turning a twenty-minute session into an hour.
Reps applies this by looking at whether the set carries load, not by guessing from the exercise name. A bodyweight pull-up gets 60 seconds. A pull-up with 25 lb on a belt is a loaded compound and gets three minutes.
When these numbers are wrong
You train in circuits. Rotating bench, pull-ups, and ab wheel for four rounds means each individual muscle rests several minutes even though you are never idle. That is antagonist or non-competing pairing, and it is why the pattern works: the rest is real, it's just occupied. Time your rest per round, not per set.
You are time-boxed. Sixty minutes with a fixed set of lifts and strict three-minute rests will not fit. Two honest options: cut the number of exercises and keep the rest, or pair non-competing lifts so rest overlaps. Both beat the third option of rushing everything, which just makes every set worse.
You are training power. Explosive work like jumps, throws, and speed-focused kettlebell swings is limited by fatigue long before it's limited by metabolic recovery. Rest until you feel fast, not until a timer says so, and stop the exercise when speed drops.
The last set was easy. These are defaults, not a prescription written for your session. If a set genuinely felt easy, starting the next one early is fine.
The number that always wins
If a set carries an explicit rest value, whether from a program you built or one you set yourself, Reps uses that and ignores the defaults entirely. The defaults exist for the far more common case, which is that nobody ever set one.
What the timer actually does
The countdown is deadline-based, not tick-based. It stores the wall-clock moment your rest ends and recomputes from there every time it draws. Put your phone in your pocket, take a call, come back: the number is correct, not however many ticks the app missed while backgrounded.
It carries two controls, on iPhone and on Apple TV alike: +30 adds thirty seconds, and × dismisses it. Adding time is the single most common thing a lifter wants from a rest timer, which is why it's a button and not a settings screen.
How long should you rest between sets?
For heavy compound lifts like squats, bench press, and rows, about three minutes. For single-joint isolation work like curls and lateral raises, about 90 seconds. For unloaded bodyweight sets, about 60 seconds. Those are the defaults 941 Reps applies automatically based on whether the set is compound and whether it carries load. Phosphocreatine, the fuel for a heavy set, refills in two phases, and the slow phase has a half-time above 170 seconds, so three minutes is where the returns start flattening rather than where recovery completes.
Is one minute of rest enough between sets?
Usually not for heavy compound work. In a controlled trial, lifters resting three minutes gained more strength and more muscle thickness than lifters resting one minute on an otherwise identical program. Short rest reduces the reps you complete on later sets, which reduces the total quality work in the session.
Does resting longer build less muscle?
No. When 21 trained men ran identical 8-week programs at one minute versus three minutes of rest, the three-minute group gained more strength and more thigh muscle thickness. The idea that short rest builds more muscle through metabolic stress did not survive the test.
How long should you rest between circuit rounds?
Time the rest per round rather than per set. In a circuit that rotates non-competing lifts, each muscle already gets several minutes between its own sets. Two to three minutes between full rounds keeps the working sets honest.
Should you rest longer for power exercises?
Yes, and judge it by speed rather than by the clock. Explosive work like jumps, throws, and speed-focused kettlebell swings is limited by fatigue well before metabolic recovery matters. Rest until the movement feels fast again, and end the exercise when speed drops.
