Introduction The UK military operates a Heat Illness Clinic (HIC) to aid the return to exercise, training and occupational duty recommendations for individuals who have suffered exertional heat illness or heatstroke. This paper describes the process of assessment and reports representative data from n=22 patients referred to the HIC.

Method The assessment included clinical consultation, and measurement of maximal oxygen consumption (V̇O₂max) and a heat tolerance test (HTT) conducted on a treadmill in an environmental chamber with an air temperature of 34°C and 44% relative humidity. Patients began the HTT wearing military clothing, carrying a rucksack (mass 15 kg) and walking at 60% V̇O₂max, at 30 min the rucksack and jacket were removed and the T-shirt at 45 min, individuals continued walking for 60–90 min. Patients were considered heat tolerant if rectal temperature achieved a plateau.

Results N=14 patients were heat tolerant on the first assessment and of the n=8 patients required to return for repeat assessment, five were heat tolerant on the second assessment and the remaining three on the third assessment.

Conclusions In conjunction with patient history and clinical evaluation, the HTT provides a physiological basis to assist with decisions concerning patient management and return to duty following an episode of heat illness.