This study, in the Journal of Applied Physiology from 2004, explored whether a cooling vest worn during an active warm-up enhances 5-km run time in the heat. Seventeen competitive runners (9 men and 8 women) completed two simulated 5-km runs in a hot, humid environment (32°C, 50% relative humidity). The athletes completed active warm-ups during which they wore either a T-shirt or a cooling vest. Results showed the 5-km run time was significantly lower (by 13 second) for those who warmed up in a cooling vest, with a faster pace most evident during the last two-thirds of the run.