Cycling competitions often take place in a warm environment which may reduce endurance performance. Whether use of a cooling vest during exercise in warm and humid environments promotes endurance is not known. Here we address this question for heavy cycling. Seven trained males were evaluated 3 times: first to determine their maximal capacities and twice during heavy cycling with or without using a light cooling vest (Flexi cold vest, Sweden, ice packs at ­20°C). After a standardised warm-up, the subjects followed a cycling protocol at 30°C and 40% relative humidity.

The subjects cycled at 60% VO2 max until exhaustion except for periods of 1 min starting after 9 min and every 10 min thereafter when cycling was at 80% VO2 max. The cooling vest was put on after 30 min. The time to exhaustion and rectal temperature after 50 min of cycling and at exhaustion were then measured.

We found that the time to exhaustion was significantly improved when the vest was used compared with the control session (72 ± 17 min vs 58 ± 7 min, respectively). After 50 min of cycling the rectal temperature did not differ between the two sessions (38.45 vs 38.54°C). At exhaustion, the rectal temperature was significantly higher in the session where the vest was used compared with the control session (39.1 vs 38.8°C, respectively). In conclusion, wearing an ice-vest during exercising in warm conditions improves endurance performance.