Half-times explained: how fast oxygen comes back
A half-time is how long it takes to win back half of the oxygen your forearm is missing. It's the simplest way to describe a refill that starts fast and then slows down.
In plain words
When you let go of a hold, oxygen starts flowing back into your forearm. It comes back fast at first and slower and slower as you get close to full. A half-time puts a number on that: it's the time it takes to win back half of what's missing. Wait one more half-time and you win back half of what's still missing, and so on. So one half-time gets you 50 % of the way back, two get you 75 %, three get you 87.5 %. A shorter half-time means a faster refill: in one lab study, elite climbers had a half-time of about 8 s, intermediate climbers about 47 s.
Memory hookEvery half-time pays back half of what's still missing.
Step by step
A worked example
Say you arrive at a rest with 40 % oxygen left in your forearm. That means 60 % is missing. Your half-time is 47 s, about what was measured for intermediate climbers.
| Time resting | Half-times | Missing before | Won back in this step | Oxygen now |
|---|---|---|---|---|
| 0 s | 0 | — | — | 40 % |
| 47 s | 1 | 60 % | 30 % (half of 60) | 70 % |
| 94 s | 2 | 30 % | 15 % (half of 30) | 85 % |
| 141 s | 3 | 15 % | 7.5 % | 92.5 % |
| 188 s | 4 | 7.5 % | 3.75 % | 96 % |
The first 47 s brought back 30 points. The next 47 s brought back only 15, and the 47 s after that only 7.5. Same rest time, less and less payback. That's why "rest until you feel fresh" rarely works, and why short rests are worth so much.
With an 8 s half-time, the same climber would reach 70 % after 8 s, 85 % after 16 s and 92.5 % after 24 s.
Try it
Move the sliders, then press Play the rest. Watch the dots at each half-time and the three bars below the chart. Then turn on Resting arm overhead.
Why the refill slows down
Refill is fastest when the muscle is emptiest. A muscle low on oxygen pulls oxygen out of every drop of blood that passes through it. As it fills up, each drop delivers less. So the refill speed is roughly proportional to the gap that's left, and a refill like that always slows the same way: half of the gap in every half-time.
Five things a half-time is not
A 47 s half-time doesn't mean "rest 94 s and you're done". After 94 s you're 75 % of the way back, not 100 %.
It's half of what's missing. From 40 %, one half-time takes you to 70 %, not to 50 %.
Measured half-times ranged from about 8 s to 95 s between groups, and individuals vary a lot within groups.
Raising the arm overhead made the half-time 2.44 times longer in one study. Gripping the rest hold hard also slows the holding arm.
Half-times after a hold to failure, after repeated grips, or after a cuff on the arm are different numbers. Only compare like with like.
Rest early or late?
Half-times also explain why it pays to rest before you're deeply pumped. Getting from 70 % back to 90 % takes about 1.6 half-times. Getting from 30 % back to 90 % takes about 2.8. At 47 s per half-time, that's roughly 75 s versus 130 s for the same end point. More on this in when to rest.
The evidence
Numbers from adults only. None of them apply to children.
- Measured Time to half recovery of forearm oxygen after a sustained 40 % grip to failure: 8 s elite, 47 s intermediate, 95 s non-climbers; after repeated grips to failure: 8, 83 and 93 s. Fryer et al. 2015: 38 adult men analysed, in four groups. J Strength Cond Res 29(6):1633–1639.
- Measured With the arm raised overhead, the half-time of oxygen recovery after a cuff test was 2.44 times longer than lying with the arm at heart level, and the recovery rate about 61 % lower. Climbing ability made no difference to this test. Štěpánová et al. 2026: 51 adult men (20 advanced to higher elite, 21 intermediate, 10 non-climbers). BMC Sports Sci Med Rehabil, 2026.
- Measured A 1 s shorter oxygen half-time after a cuff test was associated with a 0.65 grade higher red-point, adjusted for age, sex, BMI and training experience. Fryer et al. 2016: 46 adult sport climbers. Eur J Appl Physiol 116(8):1479–1484.
- Model The table and the chart assume one simple exponential curve. Real recovery has a fast early part and a slower later part, and the holding arm on a real rest recovers more slowly than a resting arm in a lab.
Model assumptions
- The oxygen level after a rest of t seconds is: start + (100 − start) × (1 − 0.5^(t ÷ half-time)).
- The time from a start level to a target is: half-time × log₂((100 − start) ÷ (100 − target)).
- Resting arm overhead multiplies the half-time by 2.44 (Štěpánová et al. 2026). That study used a cuff test, not climbing, so treat it as a guide to direction and size.
- The three bars use the measured half-times after a sustained hold, at the same start level and rest length.
Try it
Common mistakes
one half-time gets you halfway back on what's missing, not all the way.
every half-time pays back half as much as the one before.
lab half-times come from specific tests to failure, often with the arm off the wall.
the same climber refills much more slowly with the arm raised.