Is the 4-Minute Critical Force Test Accurate for Climbers? New Study Suggests Caution

A Validation Study on Critical Force

The concept of critical force (CF) is borrowed from endurance physiology, where “critical power” represents the upper boundary of sustainable work, beyond which fatigue accumulates rapidly. CF has been proposed in climbing as the local muscular analog, particularly in the finger flexors. Ideally, it should represent the highest force output a climber can sustain indefinitely under steady-state metabolic conditions.

This study puts that idea to the test using the 4-minute all-out intermittent contraction test on a hangboard, assessing whether the derived CF reliably predicts sustainable climbing-specific work.

The Study Design

Participants: 12 sport climbers (avg. IRCRA 19 ± 4)

Testing:

  • Maximal voluntary contraction (MVC).

  • A 4-minute hangboard test with 7s work:3s rest intervals to estimate CF.

  • Four verification trials at CF and reduced forces (CF −2, −4, −6 kg) to determine actual sustainable thresholds.

  • Muscle oxygen dynamics were tracked via NIRS to validate energetic/metabolic thresholds.

Important Definitions:

  • CF = mean force of last 3 contractions in the 4-min test

  • CFₘᵢₙ = minimum force from those last 3 contractions

  • CF₇₂₀ = highest force participants could maintain for a full 12-minute verification trial (720s)

What Did They Find?

1. CF Overestimates Sustainability

Only 1 of 12 participants could sustain their calculated CF for 12 minutes.

However, 92% completed the CF −6 kg trial, suggesting that the original CF was too high to represent a true critical threshold.

2. CFmin and CF720 are Better Predictors

The CFmin (end-force) agreed better with the actual sustainable force (CF720) than CF.

Statistically, CFmin had a higher correlation with climbing ability than CF (r = 0.704 vs. 0.661).

3. Muscle Oxygen (NIRS) Doesn’t Clarify the Picture Either

NIRS-derived metrics like mean StO₂ or the delayed slope couldn’t consistently differentiate sustainable vs. non-sustainable efforts.

However, the initial drop in StO₂ (during the first contraction) correlated with CF and inversely with fatigue index, suggesting some predictive value.

Physiological Insights

  • Sustained isometric contractions at high intensities (>30–50% MVC) limit oxygen delivery due to vascular occlusion.

  • The 7s contraction / 3s rest cycle may have been too metabolically demanding to reflect a true “critical” threshold, especially overhead with a crimp grip.

  • Real steady-state markers likely fall closer to CFmin or ~20% below the all-out CF estimate.

Practical Takeaways

  • If you're using the 4-min all-out test to prescribe intensity, the mean force (CF) from the end of the test likely overshoots what’s sustainable.

  • Instead, use the minimum force from the last 3 reps (CFmin) or reduce the force by ~20% to find a sustainable training intensity.

  • NIRS has potential but currently lacks precision in this setup, especially when grip shifts, arm movement, and real-world variability are involved.

Conclusion

This paper challenges using the 4-min all-out hangboard test as a reliable stand-alone tool to define critical force. While it’s simple and accessible, the way CF is typically calculated may lead to training intensities that are too high, especially for endurance or volume prescription.

A better approach may be to combine CFmin or CF720 estimates and combine them with subjective fatigue measures (like RPE) or longer-duration verification trials. And until NIRS becomes more practical in climbing, it should be used cautiously, if at all, for setting training thresholds.

 

Research:

Baláš, J., Gajdošík, J., Javorský, T., Berta, P., & Feldmann, A. (2024). Measuring critical force in sport climbers: A validation study of the 4 min all-out test on finger flexors. European Journal of Applied Physiology, 124, 2787–2798.



Tyler Nelson