Thermoregulatory Response to Exercise After Exertional Heat Stroke.

After one episode of exertional heat stroke (EHS), risk factors must be identified to determine the potential for subsequent episodes. One of these risk factors, core body temperature (Tco) kinetics during strenuous exercise, may be a surrogate marker suggestive of impaired thermoregulation. This study aimed to determine the kinetics of increases in Tco among military subjects who had a history of EHS.

Forty subjects (38 males, mean age 28.4 ± 4.9 years, mean body mass index 24.9 ± 2.4) who had a history of EHS ran 8 km in full combat gear with continuous monitoring of Tco and heart rate. The run was a qualifying event for military service. Tco was assessed using an ingestible sensor (Cortemp HQ Inc., Palmetto, Florida). Maximum oxygen uptake (VO2max) was measured on the day before the run.

The mean performance time for the run was 44.6 ± 6.6 minutes achieved under mild climatic conditions. No neurological impairment was observed. The mean maximum Tco was 39.9 ± 0.5°C. On the basis of Tco during the last 10 minutes of running, two Tco profiles were identified: increased Tco (Tco increase > 0.5°C) and plateaued Tco. Neither profile depended on initial, mid-run, or maximal Tco, VO2max, speed running, body surface area or body fat mass.

Subjects who had a history of EHS exhibited different Tco profiles at the end of an 8-km run. Laboratory studies will be necessary to identify the mechanisms underlying these profiles; future longitudinal studies can determine whether a Tco increase >0.5°C during the last 10 minutes is a risk factor for EHS recurrence.