Cardiopulmonary exercise testing after exertional heat stroke in a French military population

Exertional heat stroke (EHS) is a life-threatening emergency. However, little is known about factors that predict the occurrence and recurrence of EHS or the 'return to play' protocol after an EHS. The occurrence of an EHS in military personnel is not exceptional. The cardiopulmonary exercise test (CPX) has never been studied in military personnel or in athletes recovering from an EHS. Thus, this study aimed to analyse the CPX parameters in military personnel evaluated following an EHS.

Data were collected from 172 French military personnel prospectively included between 2014 and 2021, who underwent a CPX within 6 months of an EHS (162 cases without critical care requirement, 10 severe forms defined as a stay in intensive care and five recurrences).

The average maximal oxygen consumption (VO2max) was 44.4±7.70 mL/kg/min, that is, 111.4% of the predicted VO2max. The maximal aerobic power was 267.10±44.633 W, that is, 100.7% of the predicted value. The first ventilatory threshold was observed at 73.30%±11.44% of VO2max. The respiratory quotient was 1.10±0.10, and the ventilatory reserve was measured at 24%±24% at peak exercise. CPX did not reveal any respiratory or cardiac abnormality. The indirect value of VO2max estimated by the pre-morbid Cooper's test was 55.7 mL/min/kg. Despite the absence of specific abnormal CPX pattern in this population, post-EHS CPX suggested physical deconditioning.

This is the first study to report CPX results in a military population recovering from an EHS. The CPX results were consistent with those expected in recreational athletes, and CPX provided an objective evaluation of the level of deconditioning after EHS. This study suggests the absence of specific maladaptation to exercise in military personnel who experienced EHS. After EHS, these patients should undergo gradual, supervised retraining to prevent significant physical deconditioning.