The critical intensity of exercise, often estimated as critical power (CP), is the highest metabolic rate that can be sustained in a steady state. The purpose of this study was to compare dynamic knee extension CP between healthy males (n=12) and females (n=12) to investigate sex differences in muscle performance. Participants first completed a body composition assessment and a whole-body (cycling) test to determine maximal oxygen uptake (VO2max). To remove the confounding effects of sex differences in body composition, males and females were matched for whole-body VO2max per kg of fat-free mass (FFM; 59.5[7.9] and 59.2[6.0] mL·kg FFM-1 ·min-1 , respectively; p=0.921). Subsequently, participants completed a maximal dynamic knee extension test and four constant-workload tests to determine single-leg VO2max and CP. Single-limb VO2max was not different between males and females (22.3[3.9] and 23.8[4.0] mL·kg FFM1 ·min-1 , respectively; p=0.362). Absolute dynamic knee extension CP was greater in males (33.8[6.6] W) than females (25.4[5.6] W; p<0.05), but normalizing CP to peak power (0.75[0.11] vs. 0.73[0.07]; p=0.678), body mass (BM; 0.42[0.08] W·kg BM-1 vs. 0.39[0.09] W·kg BM-1 ; p=0.307), FFM (0.52[0.10] W·kg FFM-1 vs. 0.52[0.08] W·kg FFM-1 ; p=0.946), or leg FFM (3.01[0.50] W·kg FFM-1 vs. 3.09[0.57] W·kg FFM-1 ; p=0.715) abolished these sex differences. Overall, there was no sex difference in the critical intensity for small muscle mass exercise in fitness matched males and females. These results reinforce that the major sex difference in exercise performance is related to anthropometric differences between males and females.