Muscle recovery time by muscle group, in hours

Most recovery charts state a number of days per muscle and cite nothing. Here are the hours AIm actually uses to decide when a muscle is ready, where they come from, and the honest limits of what anyone knows.

Updated: 2026-08-31

How long each muscle takes, in hours

These are train-again thresholds: the point where the load from a hard session has effectively decayed away, not the point of full supercompensation. Published figures of six to seven days measure the second thing and do not contradict these.

Two rows usually surprise people. Arms sit at 42 hours, below quads at 48. And the lower back is the slowest thing on the list by a wide margin, at three and a half days.

Where these numbers come from, and what they are not

They are a practitioner heuristic. Not literature-derived per-muscle recovery times, because those do not exist: no study measures time-to-recovery muscle by muscle. What the research measures is damage magnitude, in a handful of muscles, and damage magnitude is not recovery time.

Two justifications this table used to carry were withdrawn after an adversarial review, and it is worth saying which:

• The fibre-type argument is gone. "Slow-twitch groups recover faster" was cited to Johnson et al. 1973, whose own data refutes the grouping: rectus abdominis is 46% type I, gastrocnemius 47 to 51%, forearm flexors 40 to 47%, all at or below the whole-body average, while the rows called slowest score higher. No human study links a muscle's fibre composition to its recovery from resistance work.
• Arms are no longer ranked slowest. Chen et al. 2011 does rank arm muscles as the most damage-prone limb muscles and knee extensors as the least, and this table used to follow that order. It no longer does, because 48 hours between direct arm work is routine for anyone who trains. Chen measured how much damage a bout causes, never how long until the next bout is reasonable.

What does hold up: hamstrings are genuinely slow on Nordic-curl data, at minus 25.6% peak torque still at 48 hours with creatine kinase peaking around 96. Belcher et al. 2019 found deadlifts need no more recovery than squats, so heavy pulls carry no extra penalty here. And the lower back at 84 hours is a coaching consensus about axial fatigue with no controlled time course behind it at all.

Three rows were never verified against anything: adductors, neck and obliques are placed by analogy with their neighbours. Treat them as the softest numbers on the page after the lower back.

What actually changes the number

The muscle is only the starting point. Three properties of the set move the window, and they matter more than the row you looked up:

• Multi-joint versus single-joint. Dourado 2022 measured 48 hours to torque recovery and 96 to edema recovery after leg press, against 24 and 48 after knee extension. Same muscle, twice the cost.
• Long-length loading. Hinges and lunges load a muscle hardest when it is stretched. That is the eccentric-emphasised class, and Sousa 2024 ties long-length eccentrics to markedly more damage. A Romanian deadlift is not a leg curl for the hamstrings even though both are hamstring work.
• Training to failure. Morán-Navarro 2017 puts the extra cost at 24 to 48 hours. Taking the last set to failure can push a 48-hour muscle past 72.

AIm applies these per set rather than per session, reading the exercise's own category and movement pattern from the catalogue instead of guessing from how many muscles a lift lists. The guess disagrees with the stated category on hip thrusts and face pulls, which is why it is only the fallback for an exercise nobody has catalogued.

Why legs need 72 hours is about the exercise, not the tissue

The oldest piece of gym folklore on this subject is that legs need three days. Look at the table and quads sit at 48 hours, the same as calves and below the chest.

Both are true at once, because the folklore is about squats rather than about quadriceps. A heavy squat is a systemically expensive exercise: it loads the lower back, which is the 84-hour row, it is multi-joint, and it is usually the set people take closest to failure. Do leg extensions instead and the quads are ready in two days. The modifiers carry the cost of the lift; the table carries the cost to the muscle.

Soreness is not the signal

Delayed onset muscle soreness tracks how unfamiliar a stimulus was far better than it tracks readiness. A new exercise leaves you sore for days without meaningfully setting back the muscle. A movement you have done weekly for a year can leave you not sore at all while performance is still down.

The usable signals are simpler: whether the weight moves the way it did last time, whether the first working set feels heavier than it should, and how long it has actually been. That last one is the only one you can plan around in advance, which is what the table is for.

Turning hours into a week

Divide 168 hours by a muscle's window and you get its ceiling on frequency, before real life intervenes:

• 36 to 42 hours means abs, forearms and arms can take direct work three times a week.
• 48 to 60 hours puts quads, lats, back and hamstrings at roughly twice a week, which is where most sensible programmes land anyway.
• 66 hours makes chest a comfortable twice a week only if the second session is lighter or shorter.
• 84 hours means heavy axial work twice in one week is already crowding the lower back, whatever the rest of the plan says.

This is a ceiling, not a target. Hitting a muscle the moment it clears the window every single week is how a programme accumulates fatigue faster than it accumulates strength. Frequency is worth adding when recovery is comfortably ahead of it, not when it is exactly level.

Seeing it instead of counting it

None of the above is worth doing by hand every week. AIm computes it from your actual logged sets: load decays exponentially from each set, overlapping sessions add up, and the result is drawn on a body map where every muscle is shaded by how loaded it still is right now. Green has cleared its window. Bright has not.

That is the practical version of this page: instead of remembering that chest is 66 hours and that Sunday's press was to failure, you look at the map and see which half of your body is ready. And because the same model sits behind the coaching, you can ask the question in words: