Muscle Recovery Time Calculator

Muscle recovery is the repair of muscle fibres after training, and the one firm number in it comes from the American College of Sports Medicine (ACSM). Its 2011 position stand asks for at least 48 hours between resistance sessions for the same muscle group. Everything else here is an estimate built around that.

What moves the number:

• The lowering phase. Eccentric work (lowering a weight under control) does far more damage than lifting it.
• Effort. Sets taken close to failure, with heavy loads, need longer.
• The session, more than the muscle. A heavy squat or deadlift day carries more total load than an arm day, which is why this page gives legs and back the longest windows. Muscle size itself is a weaker guide than people think: in a 2011 study by Chen and colleagues, the elbow flexors took more damage from the same eccentric work than the much bigger thigh muscles did.
• Training age. A muscle that has done an exercise before takes less damage from it the next time (the repeated bout effect), so beginners get the longest windows.
• Age. Recovery tends to slow from middle age, though studies disagree on how much.

Baseline recovery times

These are this page’s starting figures, for an intermediate trainee aged 30 or under sleeping 7 to 8 hours. The moderate column sits near the ACSM’s 48 hours: a little longer for legs and back, shorter for arms and core, which most lifters train more often. Everything else on the page adjusts them up or down.

The multipliers applied to those baselines:

When to use this calculator

• Planning workout splits and rest days
• Deciding whether a muscle group is ready to train again
• Adjusting frequency after stepping up intensity
• Recovering from competition or an unusually hard session

Practical example

Take a moderately fit 35-year-old doing a heavy leg day of squats, leg press and lunges, on 7 hours of sleep. Legs start at 60 hours, heavy multiplies by 1.45, intermediate leaves it alone, and being in the 31-40 bracket adds another 10%. That comes to 96 hours, so the calculator reports a window of roughly 81 to 110 hours, or about four days.

Four days between heavy leg sessions surprises people who train legs twice a week, and twice a week is the right instinct: a 2016 meta-analysis by Schoenfeld, Ogborn and Krieger found that training a muscle group at least twice a week built more muscle than once. The resolution is that most twice-weekly leg training is not heavy in the sense used here. If you can repeat Monday’s session on Thursday, Monday was moderate. Genuine near-maximal work needs the longer gap, which is why most well-run programs pair one heavy day with one lighter one rather than running two heavy days a week.

Tips for faster recovery:

• Sleep comes first. Most growth hormone is released in deep sleep, and one night without sleep cut muscle protein building by 18% in a 2021 study by Lamon and colleagues.
• 20 to 40 g of protein a meal, spread across the day. The post-workout window is far wider than the old 30-minute rule.
• Walking or easy stretching on rest days.
• Soreness (DOMS, delayed onset muscle soreness) usually peaks 24 to 72 hours after a session and is not a sign of a good one. Its absence is not a bad sign either.