Cognitive function during self-paced cycling under heat stress: Performance, perceptual, and neuromuscular fatigue...

Heat stress impairs both physical and cognitive function, yet its impact on simultaneous cognitive-motor dual-tasking (CMDT) remains unclear. Sixteen trained athletes completed two high-intensity CMDT sessions in hot (HOT, 40°C) or temperate (CON, 20°C) conditions. Each 21-min cycling exercise comprised 7-min at a self-paced 'strong' intensity followed by 14 min at a fixed-power, based on the last power selected, during which participants performed two 7-min blocks (Ex7-14, Ex14-21) of a sustained attention task (SART). Heart rate (%HR_max), rectal temperature (T_rec), and perceived mental effort were monitored, while knee-extensor neuromuscular fatigue was assessed after exercise via femoral nerve stimulation during a 1-min sustained maximal contraction. Self-paced power output was lower in HOT (198 ± 49 W) than CON (223 ± 46 W, P <0.001). %HR_max rose more steeply in HOT (interaction P <0.001), whereas T_rec did not differ between conditions (38.5 ± 0.4°C at Ex21). SART performance declined over time (-10 ± 7%, P = 0.006) but was consistently lower in HOT (64 ± 12%) vs. CON (74 ± 8%, P = 0.004), despite similar increases in perceived effort. The force loss during sustained contraction was greater in HOT (-71 ± 21%) vs. CON (-54 ± 19%, P = 0.024). Despite lower self-paced power, heat stress further impaired concurrent cognitive performance during CMDT and subsequent force production, indicating greater fatigue development.