Exercise tolerance through severe and extreme intensity domains

The power-duration relationship accurately predicts exercise tolerance for constant power exercise performed in the severe intensity domain. However, the accuracy of the prediction of time to task failure (T_lim ) is currently unclear for work rates (WR) above severe intensities; that is, within the extreme intensity domain (T_lim < 2 min). We hypothesized that T_lim would be shorter for WRs within the extreme intensity domain than predicted from the linear 1/time relationship of the severe intensity domain which would suggest mechanisms limiting exercise are different between intensity domains. Six men completed 7 knee-extension tests. T_lim of extreme intensity exercise (60%, 70%, 80%, and 90% 1RM; T_lim < 2 min) were compared to the predicted T_lim from the slope of the S1-S3 (T_lim ≥ 2-15 min) regression. Twitch force (Q_tw ) and maximal voluntary contraction (MVC) were measured on the right vastus lateralis before and after each test. T_lim at 70-90% 1RM were shorter than the T_lim predicted by the severe domain 1/time model (P < 0.05); however, T_lim at 60% 1RM was not different than the predicted severe T_lim , suggesting the mechanisms limiting extreme exercise manifest ≥60% 1RM. A significant linear relationship for 60-90% 1RM was observed which suggested a curvature constant unique to the extreme domain ( $W_{\mathrm{ext}}^{\text{'}}$ ) that was smaller than the W ' of the severe domain (1.5 ± 0.6 vs. 5.9 ± 1.5 kJ, P < 0.001). Q_tw and MVC were significantly decreased following severe exercise, however, Q_tw and MVC were not significantly decreased following 80% and 90% 1RM, giving evidence that mechanisms causing task failure were recovered by the time post-exercise measurements were made (~90 sec).