Sex Differences in the Power-Duration Relationship for Dynamic Knee Extension are Largely Explained by Muscle Size

; p=0.921). Participants completed four constant work rate tests to measure critical power (CP) and the curvature constant (W'). Using magnetic resonance imaging (MRI), quadriceps volume was assessed to estimate and control for muscle mass, and the patellar tendon moment arm (PTMA) was measured to estimate quadriceps force. Males demonstrated a significantly greater CP (p=0.003), CP torque (p<0.001), CP quadriceps force (p=0.003), and W' (p=0.036) compared to females. No sex difference in CP measures remained after controlling for quadriceps mass (p>0.05). An interaction between sex and quadriceps mass regarding W' (p=0.036) revealed a positive association in males (p<0.001) but not in females (p=0.926). After adjusting for quadriceps mass, whole-body and single-leg aerobic fitness were related to CP (p<0.05). Maximal quadriceps force was related to W' (p=0.044), but strength did not appear to influence CP independently of quadriceps mass (p>0.05). Overall, sex differences in absolute CP were largely explained by muscle size as opposed to an innate difference between male and female muscle, and variability in CP was not independently related to strength or PTMA.