Does Posing Between Sets Actually Build Muscle? The 'Flex Rest' Claim vs. the Research
Published:
Written by: Hirotsugu YoshimuraReviewed by: Tomonobu Someda
Between sets, you'll often see lifters set the weight down and flex — squeezing the biceps or quads as hard as possible. Social-media training advice frequently claims this 'flex rest' keeps the pump going and speeds up hypertrophy. But does what you do during rest actually change your gains? We compare a randomized trial that tested no-load isometric flexing between sets against a different rest-period strategy — inter-set stretching — to see which, if either, has real support.
Let the data settle it.
Does flexing/posing between sets boost hypertrophy more than passive rest?
What's said
ボディビル系のジム文化・SNSでのトレーニング解説
Flexing the target muscle hard between sets keeps the pump and blood flow going, so it should stimulate more hypertrophy than simply resting passively.
What research says
- A 2020 RCT by Schoenfeld et al. randomized 27 resistance-trained men to either passive rest or 30 seconds of maximal-effort, no-load isometric flexing after every set, over 8 weeks.
- Muscle thickness of the elbow flexors, triceps, and vastus lateralis showed no meaningful difference between groups; only the mid-thigh region showed a slight upward trend, and even that wasn't statistically decisive (the confidence interval crossed zero).
- Lower-body maximal strength (leg press 1RM) even trended slightly worse in the flexing group.
In trained men, there's no evidence that flexing between sets adds extra hypertrophy for most muscles. The mid-thigh showed a slight trend, but it comes from a single small study and shouldn't be overinterpreted.
Is it better to add some stimulus during rest rather than fully relaxing?
What's said
時短トレーニング志向のコーチング解説
Just resting passively is a waste of time. Keeping some stimulus on the muscle during rest should raise the training effect per minute spent in the gym.
What research says
- If you want to add something during rest, inter-set stretching has more support than no-load flexing.
- A 2022 review by Schoenfeld et al. concluded that stretching (loaded or passive) between sets may enhance hypertrophy, potentially through mTORC1-pathway activation suggested by animal studies.
- A handful of ~8-week human trials, mostly in untrained young men, found slightly greater muscle thickness gains with inter-set stretching.
- However, the authors themselves call this evidence 'preliminary,' and a follow-up loaded-stretch trial (Van Every et al., 2022) found a benefit only in the soleus, with no clear effect in the gastrocnemius — results vary by muscle.
If you're going to do something during rest, the current evidence leans slightly toward inter-set stretching over no-load flexing. But neither is a decisive win — the stretch evidence in particular comes mostly from untrained subjects and varies by muscle. Flexing and stretching are distinct strategies and shouldn't be conflated.
If the evidence is weak, is posing practice pointless?
What's said
トレーニング効率を重視する一部の意見
If it doesn't directly boost hypertrophy, posing practice must just be a waste of time.
What research says
- What we tested here is 'flexing as a direct hypertrophy tool' — a different question from bodybuilding posing practice as a skill.
- Posing serves practical, competition-specific purposes: stage presentation, learning how your physique reads under the lights, and judging appeal.
- None of that is what this research addresses.
- The finding is narrow — adding flexes between sets doesn't meaningfully add extra hypertrophy — not a verdict on the value of posing practice in general.
The evidence is weak for flexing as a direct hypertrophy shortcut, but that says nothing about the value of competitive posing practice. The two goals — hypertrophy strategy vs. competition skill — shouldn't be conflated.
Related research
Sources
- Schoenfeld BJ, Grgic J, Contreras B, et al. (2020) Front Physiol — To Flex or Rest: Does Adding No-Load Isometric Actions to the Inter-Set Rest Period in Resistance Training Enhance Muscular Adaptations? A Randomized-Controlled Trial
- Schoenfeld BJ, Wackerhage H, De Souza EO (2022) Front Sports Act Living — Inter-set stretch: A potential time-efficient strategy for enhancing skeletal muscle adaptations
- Van Every DW, Coleman M, Rosa A, et al. (2022) PLoS One — Loaded inter-set stretch may selectively enhance muscular adaptations of the plantar flexors
Published:
Written by
Hirotsugu YoshimuraFounder of BODYDATA / CEO of INVOLVE
I don't pick things because they "seem good." I check the data first, then test it with my own body.
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Reviewed by: Tomonobu Someda
Content reviewed from the perspective of coaching practice and supplement-industry experience
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