Cardiopulmonary function in special operations forces compared to conventional infantry soldiers

Fitness is essential to military personnel in general, especially in the special operations forces (SOF), where the demanding tasks require a high level of physical fitness and mental robustness. However, little research has been done on SOF to characterise the putative underlying cardiopulmonary adaptations that distinguish them from conventional infantry soldiers (INF). This study aims to evaluate the cardiopulmonary function in SOF compared INF. The study assessed cardiac function and dimension using transthoracic echocardiography obtained at rest in eight soldiers from a SOF unit and in eight INF. ${\dot{V}}_{O_2\max }$ was measured by direct calorimetry (secondary outcome) at the same time blood samples were collected to measure lactate levels. Lung function was assessed by spirometry, while the haemoglobin-corrected pulmonary diffusing capacity for carbon monoxide (D_L,COc) was examined by the single-breath technique. SOF had higher stroke volume (mean difference = 21 mL, P < 0.001) and left ventricular ejection fraction (mean difference = 7%, P = 0.026) than INF. Furthermore, SOF had higher global constructive myocardial work and global work index compared to INF. ${\dot{V}}_{O_2\max }$ as percentage of predicted according to age, weight and sex was higher in SOF, and they also had lower lactate levels during the ${\dot{V}}_{O_2\max }$ test than INF (P = 0.029). None of the measured lung function metrics differed between groups. In conclusion, when compared to conventional infantry soldiers, SOF soldiers had marked cardiac adaptations with evidence of eccentric LV remodelling. It remains to be determined if this reflects different training regimes or selection.