Impact of 12 weeks of basic military training on testosterone and cortisol responses.

Introduction: Military personnel train and operate in challenging multistressor environments, which can affect hormonal levels, and subsequently compromise performance and recovery. The aims of this project were to evaluate concentrations of cortisol and testosterone and subjective perceptions of stress and recovery across basic military training (BMT).

Methods: 32 male recruits undergoing BMT were tracked over a 12-week course. Saliva samples were collected weekly, on waking, 30 min postwaking and bedtime. Perceptions of stress and recovery were collected weekly. Daily physical activity (steps) were measured via wrist-mounted accelerometers across BMT. Physical fitness was assessed via the multistage fitness test and push-ups in weeks 2 and 8.

Results: Concentrations of testosterone and cortisol, and the testosterone:cortisol ratio changed significantly across BMT, with variations in responses concurrent with programmatic demands. Perceptions of stress and recovery also fluctuated according to training elements. Recruits averaged 17 027 steps per day between weeks 2 and 12, with week-to-week variations. On average, recruits significantly increased predicted VO_2max (3.6 (95% CI 1.0 to 6.1) mL/kg/min) and push-ups (5. 5 (95% CI 1.4 to 9.7) repetitions) between weeks 2 and 8.

Conclusions: Recruit stress responses oscillated over BMT in line with programmatic demands indicating that BMT was, at a group level, well-tolerated with no signs of enduring physiological strain or overtraining. The sensitivity of cortisol, testosterone and the testosterone:cortisol ratio to the stressors of military training, suggest they may have a role in monitoring physiological strain in military personnel. Subjective measures may also have utility within a monitoring framework to help ensure adaptive, rather than maladaptive (eg, injury, attrition), outcomes in military recruits.