Testing the predictive capacity of a muscle fatigue model on electrically stimulated adductor pollicis.

Purpose: Based on the critical power (P_c or critical force; F_c) concept, a recent mathematical model formalised the proportional link between the decrease in maximal capacities during fatiguing exercises and the amount of impulse accumulated above F_c. This study aimed to provide experimental support to this mathematical model of muscle fatigability in the severe domain through testing (i) the model identifiability using non-exhausting tests and (ii) the model ability to predict time to exhaustion (t_lim) and maximal force (F_max) decrease.

Methods: The model was tested on eight participants using electrically stimulated adductor pollicis muscle force. The F_max was recorded every 15 s for all tests, including five constant tests to estimate the initial maximal force (F_i), F_c, and a time constant (τ). The model's parameters were used to compare the predicted and observed t_lim values of the incremental ramp test and F_max(t) of the sine test.

Results: The results showed that the model accurately estimated F_i, F_c, and τ (CI95% = 2.7%Fi and 9.1 s for F_c and τ, respectively; median adjusted r² = 0.96) and predicted t_lim and F_max with low systematic and random errors (11 ± 20% and - 1.8 ± 7.7%F_i, respectively).

Conclusion: This study revealed the potential applications of a novel mathematical formalisation that encompasses previous research on the critical power concept. The results indicated that the model's parameters can be determined from non-exhaustive tests, as long as maximal capacities are regularly assessed. With these parameters, the evolution of maximal capacities (i.e. fatigability) at any point during a known exercise and the time to exhaustion can be accurately predicted.