This study investigated the effects of absolute humidity on heat dissipation and subsequent thermal, cardiovascular, and performance responses during self-paced exercise in the heat. Twelve trained male cyclists performed a 700-kJ time trial in four different humidity conditions (Low: 1.6 kPa, Moderate: 2.5 kPa, High: 3.5 kPa, and Very high: 4.5 kPa) in 33°C. The gradient in partial water vapor pressure at the saturated skin surface and in air, which determines sweat evaporation, decreased significantly with increasing humidity (Low: 3.53 ± 0.30 kPa, Moderate: 2.74 ± 0.24 kPa, High: 1.99 ± 0.20 kPa, Very high: 1.19 ± 0.16 kPa
p <
0.001). The maximum evaporative capacity of the environment (E