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 WR s 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% 1 RM ; 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% 1 RM were shorter than the T lim predicted by the severe domain 1/time model ( P < 0.05); however, T lim at 60% 1 RM was not different than the predicted severe T lim , suggesting the mechanisms limiting extreme exercise manifest ≥60% 1 RM . A significant linear relationship for 60–90% 1 RM was observed which suggested a curvature constant unique to the extreme domain ( ) 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% 1 RM , giving evidence that mechanisms causing task failure were recovered by the time post‐exercise measurements were made (~90 sec).

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