Purpose: Constant load cycling followed by a repeated-sprint ability test was compared in males and females under thermoneutral (TN), hot-dry (HD), and hot-humid (HH) conditions. Methods: Twenty-four trained participants (12 males and 12 females) were assessed under three conditions: TN (20°C, 40% relative humidity [RH]), HD (40°C, 35% RH), and HH (31.5°C, 90% RH), with HD and HH matched to a Wet Bulb Globe Temperature of ~31°C. Each session included 40 min of constant load cycling (7.5 W·kg-1 metabolic heat production), 5 min of passive rest, and five 6-s sprints (24-s recovery). Results: Rectal temperature reached 38.5°C in both HD and HH, compared with 38.0°C in TN (P < 0.001) after 40 min, with no sex differences (P > 0.05). Heart rate was consistently higher in HD and HH than TN from 15 min onwards (P < 0.001) during constant load cycling, with females exhibiting higher heart rates across all conditions (150 vs 146 bpm; P < 0.001). Mean and peak power output, alongside sprint decrement score, did not differ between conditions; however, males had greater sprint decrement scores than females (-9.5% vs -5.2%, P < 0.001). Conclusions: Despite higher cardiovascular strain in females, both sexes showed comparable rectal temperature to constant load cycling, indicating similar heat tolerance in the two hot conditions. The lack of differences in repeated-sprint ability between hot environments, despite 40 min of submaximal cycling, suggests that RH and ambient temperature impose comparable performance challenges during "all-out" efforts.
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