Sex differences in fatigability following exercise normalised to the power-duration relationship

Due to morphological differences, females demonstrate greater fatigue resistance of locomotor muscle during single‐limb and whole‐body exercise modalities. Whilst females sustain a greater relative intensity of single‐limb, isometric exercise than males, limited investigation has been performed during whole‐body exercise. Accordingly, this study established the power‐duration relationship during cycling in 18 trained participants (8 females). Subsequently, constant‐load exercise was performed at critical power (CP)‐matched intensities within the heavy and severe domains, with the mechanisms of fatigability assessed via non‐invasive neurostimulation, near‐infrared spectroscopy, and pulmonary gas exchange during and following exercise. Relative CP (72±5 vs. 74±2% Pmax, p = 0.210) and curvature constant (51±11 vs. 52±10 J·Pmax−1, p = 0.733) of the power‐duration relationship were similar between males and females. Subsequent heavy (p = 0.758) and severe intensity (p = 0.645) exercise time to task failures were not different between sexes. However, females experienced lesser reductions in contractile function at task failure (p≤0.020), and greater vastus lateralis oxygenation (p≤0.039) during both trials. Reductions in voluntary activation occurred following both trials (p<0.001), but were less in females following the heavy trial (p = 0.036). Furthermore, during the heavy‐intensity trial only, corticospinal excitability was reduced at the cortical (p = 0.020) and spinal (p = 0.036) levels, but these reductions were not sex‐dependent. Other than a lower respiratory exchange ratio in the heavy trial for females (p = 0.039), no gas exchange variables differed between sexes (p≥0.052). Collectively, these data demonstrate that whilst the relative power‐duration relationship is not different between males and females, the mechanisms of fatigability during CP‐matched exercise above and below critical power are mediated by sex.