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

Purpose: Based on the critical power (P or critical force; F) 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. 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) and maximal force (F) decrease.

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

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