Critical Force Test for Climbers
Critical force is the highest intermittent intensity you can sustain without fatigue building up, and it averages about 41% of maximum voluntary force in trained climbers. You find it with a 4-minute all-out test, then use it to track change and, with a margin below it, to set the loads of endurance training.
Below critical force, you can keep repeating hard grips for a long time; above it, you are spending a limited reserve that runs out in minutes. Knowing your critical force tells you how good your forearm endurance is and how hard to train it.
This article explains the concept, the test, how far to trust the number, and what to do with it.
What is critical force?
Sports scientists borrowed the idea from critical power in cycling. In climbers, critical force was defined by Giles, Fryer and colleagues in 2019, using repeated finger contractions at different intensities. They found it averages about 41% of maximum voluntary force in trained climbers, and that a single-session test agreed well with the longer multi-session method (ICC 0.90).
Two numbers come out of the model:
- Critical force (CF): the sustainable intensity.
- W′ (W prime): the reserve you can spend above critical force before you fail, like a battery.
A pumpy route is a story of both: how close to your critical force the climbing sits, and how quickly the hard sections drain your reserve.
How do you run the 4-minute all-out test?
This is the version most climbers and apps use, as described in a 2023 reliability study:
- Warm up for 10 to 15 minutes, including a few submaximal pulls.
- Set up one hand on a 20 mm edge, half crimp, with a force sensor measuring the pull.
- Pull as hard as you can for 7 seconds, then rest 3 seconds.
- Repeat 24 times without pacing. Every pull is all-out, even as your force falls.
- Read the results:
- Peak force: your highest single pull.
- Critical force (end-test force): the average of your last few pulls. Studies differ: a 2024 validation study used the last three, and the Entralpi app averages the peaks of the last sixth, 4 of 24.
- Reserve (impulse above end-test force): the area under the force curve above critical force.
- Rest and repeat on the other hand if you want both sides.
Peak force, critical force and the reserve above it, in a 24-pull all-out test.
The test is unpleasant by design. The last minute is where the number is made, so commit to every pull.
How far can you trust the result?
For tracking change, it is good. The 2023 study found peak force very reliable (ICC 0.94, 5.6% variation) and end-test force good (ICC 0.85), although end-test force varied by about 21% between days. A 2026 study found repeat all-out tests extremely consistent (ICC 0.97).
For setting loads, it runs high. The same 2026 study compared the all-out test with the classic method of several constant-force tests to exhaustion. The all-out test gave 122 N on average against 98 N, and the authors concluded it is likely unsuitable for prescribing exercise intensity.
In practice:
- Use the all-out result to see whether your endurance is improving from one block to the next.
- When you set training loads from it, aim about 20% below the result, or use the classic ratio of about 40% of your maximum as a starting point, then adjust by feel and by how sets go.
A simpler alternative: an intermittent endurance test
If the all-out test feels too brutal, a submaximal test works too. One version uses 7 seconds on, 2 seconds off at 60% of your maximum, stopping when you can no longer hold the target. In a 2022 study of 52 climbers, this test combined with maximal strength explained 46% of the variance in lead climbing ability in men and 32% in women. The authors recommend a small tolerance before stopping (about 5% below target for men and 7% for women) so a single wobble does not end the test.
How do you use critical force in training?
- Just below critical force (long sets of repeaters, or easy continuous climbing): builds the aerobic capacity of the forearm, which raises critical force itself. See our article on aerobic endurance on the hangboard.
- Well above critical force (short, hard intervals): trains the size of your reserve and your tolerance to it. See repeaters.
- On the wall: researchers have found a matching “critical angle” on a treadwall. Climbing just 2° steeper than it led to failure in about 16 minutes, while 2° below it could be sustained for 20 minutes at moderate effort.
What do you need to run the test?
The all-out test needs a device that records every pull, not just the peak: an inline load cell or a force plate. On a ground force plate like Entralpi, you stand on the plate and pull on your hangboard’s 20 mm edge; the 2023 reliability study above ran this test on an Entralpi plate. A crane scale sends only a few readings per second: some community apps run the test with one, but the result is rougher. See our device comparison and the full testing guide.
More on testing and endurance: how to test finger strength, finger endurance training and repeaters.
Do this in Entralpi
The app’s endurance test is a 4-minute all-out test with one hand. It gives your critical force and your sustainable force (The endurance test). Endurance, recovery and rehab workouts set their targets from the sustainable force, and What each test measures explains each number.
Sources
- Giles D, et al. (2019). The determination of finger-flexor critical force in rock climbers. International Journal of Sports Physiology and Performance.
- McClean ZJ, et al. (2023). Test-retest reliability of a 4-minute all-out critical force test in rock climbers. International Journal of Exercise Science.
- Boklaschuk P, MacDougall K, MacInnis M (2026). The validity and utility of the all-out test for forearm flexor critical force. European Journal of Applied Physiology.
- Augste C, Winkler M, Künzell S (2022). Optimization of an intermittent finger endurance test for climbers regarding gender and deviation in force and pulling time. Frontiers in Sports and Active Living.
- Baláš J, Gajdošík J, Giles D, Fryer S (2022). The estimation of critical angle in climbing as a measure of maximal metabolic steady state. Frontiers in Physiology.
