This study evaluated how preparing for an interval workout, while wearing a cooling vest, affects core temperature (Tc), heart rate (HR), and interval time in long-distance runners. Nineteen male collegiate cross-country runners exercised under two different conditions: (a) wearing a Nike PreCool" ice vest for one hour prior to the workout (30 minutes resting with the vest and 30 minutes while performing their warm-up); and (b) a control condition utilizing a traditional warm-up. Subjects performed 8 ? 1000 m intervals. HR and Tc were measured prior to warm-up, immediately before the first interval, and after each interval. Tc measured before the first interval was significantly lower in the vest condition (difference = 0.37? ? 0.2?C). Differences persisted through the sixth interval. Differences in HR and interval times were nonsignificant between conditions for all intervals. Wearing an ice vest prior to and during warm-up effectively lowers Tc during long-distance interval training.