Resting longer between sets did not build more muscle in this trial. In an 8-week study of resistance-trained adults, lifters who chose their own rest averaged about 3.7 minutes between sets. They gained the same muscle thickness, strength, and endurance as lifters held to roughly 2 minutes, and their sessions took about 29% longer. For most hypertrophy-focused work in the 8-12 rep range, a timed rest of about 2 minutes gives the same results in less time.

This hypertrophy study, from Brad Schoenfeld's lab and collaborators, adds to the strength training research on rest intervals. Its angle is useful because it skips the usual question of short versus long rest. Instead it asks what happens when lifters simply rest as long as they feel they need. The answer is that, left to their own judgment, trained lifters rest longer than they need to.

Key Finding

Self-selected rest and fixed ~2-minute rest produced practically identical muscular adaptations over 8 weeks of lower-body training. The only meaningful difference was time.

The fixed-rest group finished sessions in about 56 minutes. The self-selected group needed about 78.5 minutes. Both groups rated the sessions as equally hard.

Study Details

Researchers randomized 40 resistance-trained adults into two groups:

  • SELF (n = 21): rested as long as they wanted between sets
  • FIXED (n = 19): rested approximately 2 minutes between sets

Both groups did 8 weeks of supervised lower-body training. Each session included four sets of 8-12 repetitions on four exercises:

  1. Back squat
  2. Leg extension
  3. Standing calf raise
  4. Seated calf raise

The researchers measured these outcomes:

  • Muscle thickness, using ultrasound
  • Dynamic and isometric strength
  • Muscular endurance
  • Total training time
  • Session RPE (rating of perceived exertion)

The analysis was Bayesian. Results are reported as effect sizes with credible intervals rather than simple p-values. This approach shows how large an effect is likely to be, not only whether one exists.

Results

Both groups improved meaningfully on every outcome, and neither group clearly outperformed the other. The key numbers:

  • Hypertrophy domain: treatment effect of -0.1 SD (95% CrI: -0.2 to 0.0). The difference is trivial, with a slight lean toward the fixed group, if anything.
  • Performance domain: treatment effect of 0.0 SD (95% CrI: -0.3 to 0.3). There was no difference between groups.
  • Average rest per set: about 3.7 minutes for SELF, compared with about 2.4 minutes actually taken by FIXED, according to reporting on the preprint.
  • Session duration: 56.0 ± 4.5 minutes for FIXED and 78.5 ± 15.4 minutes for SELF.
  • Session RPE: 8.2 ± 1.0 for FIXED and 8.1 ± 0.7 for SELF.

Two details deserve attention.

The first is the spread in the self-selected group's session times. A standard deviation of 15.4 minutes means some lifters in that group trained close to an hour while others went well past 90 minutes. Fixed rest made sessions predictable. Self-selection made them highly variable.

The second is effort. The longer rest periods did not make sessions feel easier, and the shorter ones did not make them feel harder. Both groups rated sessions at about 8 out of 10. The extra rest did not buy a better training experience, either.

Why This Matters in Context

Earlier work from the same lab, notably Schoenfeld et al. (2016) in the Journal of Strength and Conditioning Research, found that 3-minute rest periods outperformed 1-minute rest periods for strength and hypertrophy in trained men. This new study does not contradict that finding.

Read together, the two studies suggest a threshold rather than a rule of "more is better." Very short rest can reduce how much quality work you get done. Once rest reaches about 2 minutes for moderate-rep work, adding more appears to bring diminishing or no returns.

Limitations

The study is well designed, but its findings have clear boundaries:

  • Lower body only. It covered squats, leg extensions, and calf raises. The results may not transfer directly to upper-body training, which uses smaller muscle groups and loads more of the shoulders.
  • One rep range. All work was done in the 8-12 rep range. Heavy strength work in the 1-5 rep range, especially on demanding compound lifts, is a different stimulus and may benefit from longer rest. This study did not test that.
  • Short duration and small sample. Eight weeks with 40 participants can reveal moderate effects. It cannot rule out small differences that would only appear over months or years of training.
  • Only one compound lift. The squat was the only heavy multi-joint movement. Sessions built around several heavy compound lifts may accumulate more fatigue than this protocol did.

What This Means for Your Training

The most practical takeaway is this: your sense of when you're "ready" for the next set is probably conservative. Trained lifters in this study chose more than 50% more rest than the fixed group took, and the extra time did nothing measurable for them.

Here is how to apply that.

  1. Set a default of 2 minutes for hypertrophy work. For sets of 8-12 reps on most exercises, start the next set when a timer reaches 2 minutes, not when you feel ready.
  2. Allow more rest for heavy compound lifts. For low-rep work on squats, deadlifts, or bench press, 3 minutes or more remains a reasonable choice. This study does not argue against it.
  3. Use rep performance as your signal. If your reps on a given exercise fall sharply from one set to the next at 2 minutes, for example from 12 to 8, try extending rest on that lift. If your reps hold steady, 2 minutes is enough.
  4. Do the time math. A difference of about 22 minutes per session adds up. If you trained legs twice a week, that would be roughly 45 minutes saved weekly. You could spend that time on extra volume for lagging muscle groups or simply shorten your training day.
  5. Value predictability. A 56-minute session that reliably fits your schedule is easier to repeat for years than a session that varies between 60 and 95 minutes. Consistency over the long term matters more than any single rest-interval decision.

Rest only works if your sets keep their quality, so the variable to watch is rep performance across sets. When your logs show that reps hold steady at 2 minutes, you have personal evidence that matches the study.

How This Fits Into Your Training Log

When you record every set, Kenso's progression engine can show whether 2-minute rest keeps your reps on target. To check your logs and decide where to add rest, ask the Kenso AI coach whether your rest intervals are costing you reps.

The Bigger Picture

Evidence-based training often means ignoring instincts that feel productive. Resting until you "feel recovered" seems sensible, but this study suggests that feeling arrives later than your muscles need.

The good news is that you don't need longer sessions to keep making progress. Structured rest, consistent effort, and careful tracking of what you actually lift will carry you further than extra minutes on the bench. Kenso is built around that idea: fewer guesses, more data, and progression you can measure.

FAQ

How long should I rest between sets for hypertrophy?

For moderate-rep work of 8-12 reps, about 2 minutes appears sufficient for trained lifters, based on this study. In it, resting longer by choice, about 3.7 minutes on average, produced no extra muscle growth.

Does resting longer between sets increase strength?

In this study, it did not. Strength and endurance improved equally in both groups. For heavy low-rep training, longer rest may still help, but this study did not test that.

Why did the self-selected group rest so long?

The study did not identify a single cause. A likely explanation is that perceived readiness lags behind actual recovery. Session RPE was nearly identical between groups, so the extra rest did not make training feel any easier.

Do these findings apply to upper-body training?

Not directly. The study tested only lower-body exercises. The principle that about 2 minutes is enough for moderate-rep work is a reasonable starting point for upper-body training, but you should check it against your own rep performance across sets.

Should I time my rest periods?

Yes. Timing your rest is a simple way to keep sessions efficient and predictable. Pair it with logging your reps so you can see whether your rest intervals are holding up your set quality.

Ready to Train With Intention?

If you want your training decisions guided by your own data instead of guesswork, Kenso can help. Log every set, let the progression engine tell you when to add load or reps, and ask the AI Coach how findings like this one apply to your program. Download Kenso on iOS and start building a training history you can learn from.

Citation

Mohan AE, Piñero A, Coleman M, Hopper A, Segtnan R, et al. Freedom of Choice? Effects of Self-Selected Rest Intervals on Muscular Adaptations. International Journal of Sports Medicine. DOI: 10.1055/a-2999-0052. PubMed: https://pubmed.ncbi.nlm.nih.gov/42994440/

Also referenced: Schoenfeld BJ, Pope ZK, Benik FM, 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.