Thermal responses of men and women during cold-water immersion: influence of exercise intensity

Summary The influence of exercise intensity on thermoregulation was studied in 8 men and 8 women volunteers during three levels of arm-leg exercise (level I: 700 ml oxygen (O₂) · min^–1; level II: 1250 ml O₂ · min^–1; level III: 1700 ml O₂ · min^–1 for 1 h in water at 20 and 28°C (T _w). For the men inT _w 28°C the rectal temperature (T _re) fell 0.79°C (P<0.05) during immersion in both rest and level-I exercise. With level-II exercise a drop inT _re of 0.54° C (P < 0.05) was noted, while at level-III exerciseT _re did not change from the pre-immersion value. AtT _w of 20°C,T _re fell throughout immersion with no significant difference in finalT _re observed between rest and any exercise level. For the women at rest atT _w 28°C,T _re fell 0.80°C (P<0.05) below the pre-immersion value. With the two more intense levels of exercise,T _re did not decrease during immersion. InT _w 20°C, the women maintained higherT _re (P<0.05) during level-II and level-III exercise compared to rest and exercise at level I. The_{T re} responses were related to changes in tissue insulation (I _t) between rest and exercise with the largest reductions inI _t noted between rest and level-I exercise acrossT _w and gender. For men and women of similar percentage body fat, decreases inT _re were greater for the women at rest and level-I exercise inT _w 20°C (P< 0.05). With more intense exercise, the women maintained a higherT _re than the men, especially in the colder water. These findings indicate that exercise is not always effective in offsetting the decrease inI _t and facilitated heat loss in cool or cold water compared to rest. The factors of exercise intensity,T _W, body fat, and gender influence the thermoregulatory responses.