Factors affecting the estimation of physical working capacity at the fatigue threshold

The purpose of this study was to investigate potential improvements in the methodology associated with the Physical Working Capacity at the Fatigue Threshold (PWC_FT) test including: (1) the use of a continuous test protocol; (2) the use of a treadmill; (3) the use of a bipolar EMG lead system for noisy electronic environments; and (4) the potential for residual fatigue from tests repeated 24 hours apart. The results of the continuous test protocol (X¯ ± S.D. = 210±73 watts) correlated well (r = 0·856) with the original discontinuous technique (222± 83 watts) and there was no significant (p> 0·05) difference between the mean values (t= 1·146). Treadmill testing required a bipolar lead system to counteract the electrical noise generated by the treadmill motor. The heart rate values which corresponded to PWC_FT on the treadmill (W¯+s.d. = 164±b.p.m.) and bicycle ergometer (153 ± 18 b.p.m.) were highly correlated (r=0·833) and there was no significant (p>0·05) difference between the mean values (t= 2·22). The use of a bipolar lead EMG system on the bicycle ergometer resulted in significantly (p<0·05) smaller voltage for any given power output, and the PWC_FT exhibited a low to moderate correlation (r=0·60) with PWC_FM derived from a unipolar arrangement. The test-retest results of discontinuous PWC_FM measurements performed 24 hours apart on the bicycle ergometer were correlated at r=0·812 with no significant (p>0·05) difference (=0·52) between the mean values (test=198±60; retest=191±63 watts).It was concluded that the continuous protocol using a bicycle ergometer should be considered an attractive alternative to the original discontinuous PWC_FM test, and daily testing (using the discontinuous procedures) resulted in no residual fatigue. The use of a treadmill or bipolar lead system for the determination of PWC_FM requires further study with respect to both validity and reproducibility.