Fatigue profile: A numerical method to examine fatigue in cycle ergometry

Fatigue Profile, a new numerical method for characterising fatigue in isokinetic cycle ergometry is presented and compared with the conventional fatigue index (FI). The new method describes the temporal development of muscle fatigue based on the decline of peak power output throughout a whole trial. The advantage of this method is demonstrated by the analysis of two 25 s maximum trials, separated by 90 s recovery, performed by a well-trained athlete at a pedal frequency of 120 revolutions per minute. A fourth degree polynomial was fitted to model the peak power data. Using the polynomial model coefficients the first derivative represented the rate of changing peak power which represented the Fatigue Profile. The conventional FI was calculated as -35 Ws^-1 and -32 Ws^-1 for trials 1 and 2 respectively, indicating minor differences in fatigue between trials. In contrast the Fatigue Profile revealed important numeric and temporal differences between the trials. For trial 1 a maximum rate of peak power decline of -65 Ws^-1 was reached at approximately 6 s into the trial. In marked contrast, in trial 2, maximum rate of peak power decline (-146 Ws^-1) occurred immediately. The Fatigue Profile approach allows the characterisation of the temporal development of fatigue under different experimental conditions and in combination with other techniques may yield further insight into the underlying mechanisms of fatigue.