Sex Differences in the Severe‐ and Extreme‐Intensity Power‐Duration Relationships

Abstract

We have previously shown that, similar to the severe‐intensity power duration relationship (i.e., W’sev), there exists a separate, smaller power‐duration relationship for the extreme‐intensity domain (W’­ext) in men. We have also shown that there may be differences in contributions of central and peripheral fatigue between men and women during and immediately following extreme‐intensity exercise. The current study tested the hypotheses that 1) the W’extwould be significantly less than W’sev in both sexes, but not different between men and women, 2) absolute Maximum Voluntary Contractions (MVC) would be reduced to greater extent at end‐exercise following severe‐ and extreme‐intensity exercise in men compared to women but not when scaled relative to baseline, and 3) peripheral fatigue would be greater at task failure (Tlim) in men compared to women following severe‐intensity exercise, with no sex difference following extreme‐intensity exercise. Following familiarization, 7 men and 7 women completed three severe‐ (Tlim: 2‐4 min, S3; 5‐7 min, S2; 8‐12 min, S1) and three extreme‐intensity (70, 80, 90% MVC) isometric knee‐extension bouts to task failure. MVC and potentiated twitch force (Qpot) were measured and compared at baseline, task failure, and 150 s of recovery. W’ext was significantly smaller compared to W’sev in men (2.4 ± 1.2 kJ vs 3.9 ± 1.3 kJ; p = 0.03) and in women (1.6 ± 0.8 kJ vs 2.9 ± 1.7 kJ; p = 0.05), however there were no sex differences in either W’extor W’­sev. There were no sex differences in MVC at task failure following severe‐intensity exercise. However, MVC was lower in women following extreme‐intensity exercise compared to men, although there were no sex differences in MVC relative to baseline. Further, there were no differences in MVC by the end of recovery compared to baseline in men or women following extreme‐intensity exercise.Qpot was not different at task failure following severe‐ and extreme‐intensity exercise between men and women. However, men showed lower Qpot relative to baseline, suggesting greater peripheral fatigue development, with the exception of exercise at 90% MVC. These data provide evidence that important sex differences exist in the contributions of peripheral fatigue to task failure and in recovery from exercise which depend on exercise intensity. Therefore, practitioners need to consider exercise intensity and the time course of recovery when prescribing exercise to men and women.