Abstract

The effect of slightly lowered body temperature on endurance time and possibly related physiological factors was studied in seven male volunteers exercising on a cycle ergometer at an ambient temperature (Ta) of 18 degrees C. Work load was increased to 40 in a stepwise manner (phase I, min 0-16) followed by a period at 80 of peak oxygen (VO2) sustained to exhaustion. On one day, exercise was preceded by a double cold exposure (precooling test, PRET), resulting in a 204-kJ/m2 negative heat storage and a 4 and 0.2 degree C lower mean skin and core temperature at the start of exercise compared with the control test (CONT). Core temperature dropped further during exercise in PRET. Endurance time at 80 of peak VO2 was increased by 12 in PRET. Heart rate (HR) was decreased throughout PRET; oxygen pulse and arteriovenous O2 difference were significantly increased in phase I of PRET, whereas the PRET-CONT differences i stroke volume and cardiac output were not significant. In phase II of PRET (min 16-28), heavy exercise) sweat rate (SR) and heat conductivity, indicating forearm blood flow, were lower. Pedal rate (PR) was 9 lower in phase II of PRET. At the termination of exercise, PRET-CONT differences in HR, SR, and PR had disappeared. Verf.-Referat