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 (tau). 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 tau (CI95% = 2.7%Fi and 9.1 s for F-c and tau, respectively; median adjusted r(2) = 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.