Climbing Critical Force Calculator

Critical Force Calculator

The Critical Force Calculator will help you determine where you stand with your forearm aerobic endurance. If you’re a strong sport’s or trad climber, but end up pumped on your way to the crux, it means that your forearm aerobic endurance likely requires some attention. The Critical Force Calculator will also allow you to find the optimum load at which you should train so that you will soon breeze up through those endurance routes!

For best results, train exactly at CF intensity and try to maximize the total work done.


To determine your forearm aerobic endurance Critical Force, you can use the calculator below. Input your body weight and your 7-second MVC on a 20 mm edge, followed by respective times to failure for the 7/3 Endurance Repeaters at 80% MVC-7 and 60% MVC-7. For the last measurement you may choose 45%, 50% or 55% MVC-7 load, just make sure that you fail in under 1200 seconds.

The calculator will output your CF and the weight you need to subtract in order to exercise exactly at CF load. You will also receive a brief assessment of your strength and forearm aerobic endurance. The calculator is calibrated for the half crimp grip on a 20 mm edge, to enable a direct comparison with the results published in [1]. The bouldering level prediction is based on the results of the survey published at [2].

You can find more detailed information regarding the role of the Critical Force in sport’s and climbing endurance training in [3]

Example Critical Force test

Let’s say you weigh 68 kg, and you take the MVC-7 test on a 20 mm edge. You can add 32 kg to the bodyweight and hang for 7 seconds, so the MVC-7 load is 100 kg. Now we can calculate your 80%, 60% and 45% loads, which are 80 kg, 60 kg and 45 kg respectively.

  1. Test your T80% :
    • To set the 80% load, you must add 12 kg to the harness.
    • Execute a set of 7/3 Repeaters until failure.
    • Add the hanging times together. This means that if you were able to execute 10 full hangs and failed at hang 11 in the 4-th second, then your T80% is 74 seconds.
    • Rest 15 minutes before the next test.
  2. Test your T60%
    • To set the 60% load, you must remove 8 kg using a pulley system.
    • Execute a set of 7/3 Repeaters until failure.
    • Add the hanging times together. This means that if you were able to execute 15 full hangs and failed at hang 16 in the 4-th second, then your T60% is 109 seconds.
    • Rest 30 minutes before the next test.
  3. Test your T45%:
    • To set the 45% load, you must remove 23 kg using a pulley system.
    • Execute a set of 7/3 Repeaters until failure.
    • Add the hanging times together. This means that if you were able to execute 60 full hangs and failed at hang 61 in the 4-th second, then your T45% is 424 seconds.
    • If your aerobic endurance is very good, and you are able to last more than 20 minutes at the 45% load, you should change the load to 50% or even 55% of your MVC-7 and redo the test.
  4. Enter your data into the form and press calculate.
kg lbs
T(45%) [s]
T(50%) [s]
T(55%) [s]


The idea of Critical Force

Critical Speed (CS) and Critical Power (CP) are well-known concepts used in sports training. Imagine yourself walking at about 6 km/h – you could probably carry on like this for hours. On the other hand, unless you’re an elite marathon runner, you probably couldn’t run at 20 km/h for very long. This means that your running critical speed, which is the speed at which you could theoretically run for an unlimited time, lies somewhere between 6 – 20 km/h. Cycling coaches use the term Critical Power, which defines the power output, at which you could cycle for hours. For climbing, the term Critical Force (CF) is more relevant, meaning the maximum load at which you should be able to climb indefinitely without falling off.

The Critical Force determines the performance on endurance routes, and it is directly related to the forearm aerobic capacity. Critical Force is usually expressed as a percentage of the climber’s body weight, or their maximum voluntary contraction (MVC). For elite sport climbers, it could reach up to 60% of their MVC, while for boulderers and poorly conditioned route climbers, it could be below 30% MVC. Knowing your CF is important because it was shown that aerobic capacity is trained most efficiently exactly at critical loads [4].


  1. Giles, D., Chidley, J.B., Taylor, N., Torr, O., Hadley, J., Randall, T., Fryer, S., 2019. The Determination of Finger-Flexor Critical Force in Rock Climbers. International Journal of Sports Physiology and Performance 1–8. (link)
  2. (link)
  3. J. Banaszczyk, StrengthClimbing – Endurance Repeaters, May 2, 2019. (link)
  4. McGawley, K., 2010. The application of the critical power construct to endurance exercise. University of Brighton. Student thesis: Doctoral Thesis. (link)

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5 thoughts on “Climbing Critical Force Calculator”

    1. Hi Tom! Thanks for the question! Every time you execute a hang that’s close to your limit, you burn phosphocreatine (PCr), which is used to produce ATP that fuels your muscles. It takes between 3 – 5 minutes to replenish the PCr stores after such a maximum effort completely. The longer you hang, the more you deplete PCr, and the longer you need to rest. So, for example, after a single MVC-7 attempt, it might be enough to rest 3 minutes, but after a 30-second hang, it possible that you would have to rest even 10 minutes to recover fully.
      To determine the MVC-7 with reasonable accuracy, you need to perform at least 3 – 4 hangs, and the fatigue might start to accumulate, even if you rest for 5 minutes after each hang. To stay on the safe side, I think it’s better to wait 10 – 15 minutes after the MVC-7 tests and before moving on to the 80% Repeaters.

  1. My results are as follows:
    Mvc-7 115kg. (60kg bw +55kg)
    T80 = 23s
    T60 = 91s
    T50 = 112s
    I used to just be able to hang 50kg at a push, but the 55kg felt ok, and i failed at the 6th second for 60kg.

    1. Hi Tom!
      Thanks for posting your results! First of all, I need to congratulate you on your finger strength! At 55 kg added weight, you probably boulder around V11 🙂
      I took a closer look at the results of your Critical Force test. My guess is that you did the 50% test because, at 45% MVC, you were able to make it past the 20-minute mark, am I right? I plotted your results on the graph below.
      The green line is a typical characteristic measured for one of the climbers who follow my training plan. The person is a typical route climber, with a pretty decent CF score of 49% MVC-7.
      The red squares are your measured results, and the blue line is the endurance curve calculated for your measured T50%. The T50% result lies below the curve, which means that the result is too low – it does not fit the theoretical model. It should be around 190 seconds.
      The gray dashed line is the endurance curve, calculated assuming that your T45% result was 840 seconds, which is equivalent to completing full 20 minutes of the exercise. The curve is almost the same as the curve plotted using T50%. This confirms that your measured T50% result is too low.
      The T60% measurement seems just right, and the T80% measurement seems also slightly low – it should be at least 40 seconds.
      To sum up, it looks like you were still tired from the MVC-7 measurements when you did the 80% measurement. Then you took a good rest and measured T60% correctly, and then you were tired again when doing T50%. Perhaps you measured after testing for T45% first.
      Still, it’s obvious that you are a very strong boulderer and sport climber. Based on your results, I believe that you should be able to project in the 8b – 8b+ range. But there is certainly room for improvement when it comes to your endurance. If you could increase your CF from 45% MVC-7 to 50% MVC-7, which is common among sport climbers, you could make big progress.
      Anyway, I hope this helped.

  2. I am definitely an outlier. I just took the rest times that were given in the example. I also didnt try the t45 just because i had the right weight for t50. I was curious that my times were much much lower than the given examples. I have been sportclimbing 20 years and never really bouldered, the hardest i climbed was 5.13c/14a and maybe a small amount in the 5.13 range. My max hang used to be +50kg but i tried a different training tool and managed to surpass it. Im continuing to use it to make sure it is what is increasing my finger strength.

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