Why resting works: oxygen in the forearm
A hard grip squeezes shut the blood supply to the forearm. Letting go reopens it, and oxygen floods back: fast at first, then more slowly.
In plain words
Your finger muscles sit in your forearm and need oxygen from the blood to keep working. When you grip hard, the muscles squeeze their own blood vessels shut, so the oxygen runs out and you get pumped. When you relax the grip, or let the arm hang and shake it, blood flows back in and the oxygen refills. The refill is quick at the start and slows down as you near full, so the first part of a rest is worth the most. Trained climbers refill much faster than beginners.
Memory hookSqueeze shuts the tap, let go and it pours; the first seconds are worth the most.
What happens in a gripping forearm
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You grip the hold hardGrip
The finger flexor muscles press on the vessels inside the forearm.
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Blood flow drops, then stopsFlow
Above roughly half of your maximum grip, fresh blood can no longer get in.
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The muscle uses up its oxygenOxygen
Effort continues on stored oxygen and energy until it runs low: the pump.
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You let go or shakeRelease
The vessels reopen and oxygen-rich blood returns.
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Oxygen climbs back upRefill
Fast at first, then slower as it approaches the resting level.
The tap and the squeeze
The harder you grip relative to your maximum, the less blood gets through. Studies place the point where flow stops somewhere between about 45 and 75 % of maximum grip force. Where you fall in that range depends on the person and the muscle. Gripping harder than a hold needs costs you twice: you use more oxygen, and less of it gets in.
Refill is fast at first, then slows
Recovery is easiest to describe by its half-time: how long it takes to win back half of the oxygen you lost (half-times explained goes through it step by step). After the first half-time you're halfway back, after two you're three-quarters back, after three seven-eighths. That's why a short shake on every reasonable hold often beats one long rest on a poor one.
Why the shaking hand should hang low
Shaking with the arm hanging down beside the body brought oxygen back faster than keeping the hand up near the hold, and it lengthened a repeated-grip test. Raising the arm above the heart slows the refill a lot, and shaking low helps empty the veins; arm position on a rest explains why.
See it
Pick a rest hold and a refill half-time, then press play. One arm holds while the other shakes, and they swap every few seconds.
The evidence
All numbers below come from adults. Do not apply them to children.
- Measured Half recovery of forearm oxygen after a sustained 40 % grip held to failure took about 8 s in elite climbers, 47 s in intermediate climbers and 95 s in non-climbers (deep finger flexor, open crimp, passive recovery). After a repeated-grip test the values were 8, 83 and 93 s. Fryer et al. 2015: 44 adult men recruited, 38 analysed, in four groups (non-climbers, intermediate, advanced, elite). J Strength Cond Res 29(6):1633–1639.
- Measured Shaking the hand beside the body gave 22 % longer repeated-grip test time and 32 % faster re-oxygenation than resting with the hand over the hold. Baláš et al. 2016: 22 adult rock climbers, tests at 60 % of maximum grip. Eur J Sport Sci 16(7):764–772.
- Measured Forearm blood flow is cut off at roughly 45–75 % of maximum grip force. Barnes 1980, Ergonomics 23(4):351–357, as cited by MacLeod et al. 2007 (11 intermediate climbers and 9 non-climbers, tests at 40 % of maximum): J Sports Sci 25(12):1433–1443.
- Coaching practice Switch hands every few seconds on a rest, and shake on any hold that allows it rather than waiting for one big rest.
- Model Treating refill as a single half-time curve is a simplification. The studies measured recovery with the arm at rest off the wall, not on a route.
Model assumptions
The forearm model on this site assumes full blood flow below 20 % of maximum grip, falling in a straight line to zero at 60 % (the middle of the measured 45–75 % range). It also assumes oxygen use proportional to grip force, and refill toward 100 % with the half-time you choose, 1.32 times faster when the arm hangs low. These are illustrative choices, not measurements.
Try it
The rest hold is worse than it looked: stay and shake, or leave now?
Rest-hold refill drill: practise switching hands and shaking low on a real rest.
Common mistakes
squeezing harder than the hold needs uses oxygen and shuts the tap at the same time.
let the arm hang low beside the body; measured as faster re-oxygenation.
refill slows as you approach full; on a poor hold you may never get there.
the first seconds of any shake recover the most oxygen.