Primary metabolic acidosis induced by four days of simulated combat training: impact of strenuous physical exercise, sleep deprivation, and food restriction

The military population relies on being mentally and physically healthy to perform well during operations. Recent studies indicate that multiple stressors during combat training influence both acute and chronic stress responses in soldiers, ultimately affecting their performance and health. This study investigated the physiological effects of strenuous physical activity, mental strain, sleep deprivation, and energy deficits during four days of simulated combat training (SCT) by analyzing changes in body composition and blood biomarkers, focusing on metabolic changes. This cohort study with a pre- and post-design included 48 cadets (12 females and 36 males) from the Royal Norwegian Air Force Academy, aged 20-29 years, who participated in mandatory SCT. Body composition was measured using bioelectrical impedance (InBody 770), and blood biomarkers were collected through blood samples and capillary blood gas. We observed a significant decrease in total body weight following SCT, including reductions in total body water, muscle mass, and fat mass. Metabolic markers such as pH, pCO2, and base excess were significantly decreased, while the anion gap significantly increased. Lactate levels showed no significant change following SCT. All electrolyte and nutritional markers (triglyceride, glucose, sodium, calcium, and chloride) significantly decreased, except for potassium, which showed no change. These findings support the necessity for comprehensive monitoring and management of metabolic acidosis, electrolyte imbalances, and hydration status in soldiers undergoing SCT. Ensuring sufficient nutrition, hydration, and recovery time is crucial to reduce negative health effects and maintain optimal performance during and following SCT.