Hypothermia can occur during aquatic exercise, despite production of significant amounts of heat by the active muscles. Because the characteristics of human thermoregulatory responses to cold during exercise have not been fully elucidated, we investigated the effect of low-intensity exercise on the shivering response to core cooling in cool water. Eight healthy young men (24±3 years) were cooled through cool water immersion while resting (rest trial) and during loadless pedaling on a water cycle ergometer (exercise trial). Before the cooling, body temperature was elevated by hot-water immersion to clearly detect a core temperature at which shivering initiates. Throughout the cooling period, mean skin temperature remained around the water temperature (25°C) in both trials, while esophageal temperature ( T) did not differ between the trials ( P>0.05). The T at which oxygen uptake (V(・)O) rapidly increased, an index of the core temperature threshold for shivering, was lower during exercise than rest (36.2±0.4°C vs. 36.5±0.4°C, P<0.05). The sensitivity of the shivering response, as indicated by the slope of the T-V(・)O relation, did not differ between the trials (-441.3±177.