Sex differences in performance loss above critical power in professional cycling are underexplored, yet crucial for tailoring training and race strategies. This study examined sex-specific differences in performance loss above critical power across accumulated work levels and effort durations in elite cyclists. Power output data from 16 female and 17 male WorldTour professionals were analyzed over one season. Performance loss was quantified after 1-5 kJ kg-1 accumulated work above critical power ((power output - critical power) dt for power output>critical power, normalized to body mass). Power decay was assessed for efforts of 5 and 30 seconds and 1, 5, 10, and 20 minutes. A small sex difference emerged at 1 kJ kg-1 (women: 3.73±4.12% vs. men: 2.44±4.23%, p=0.031, and d=0.31), with no differences at 2-4 kJ kg-1. At 5 kJ kg-1, men showed less loss (women: 29.58±29.35% vs. men: 16.58±10.44%, p<0.001, and d=0.60). Women exhibited greater decay in 5-minute efforts from 1 kJ kg-1 (p=0.001) and 10-20 minute efforts from 1 to 2 kJ kg-1 (p<0.05), with gaps widening at higher work levels. Men had higher estimated maximum oxygen uptake and critical power, enabling better sustainability under high-intensity fatigue, likely due to superior aerobic capacity.
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