Impact of military training stress on hormone response and recovery

Abstract

Objectives Military personnel are required to train and operate in challenging multi-stressor environments, which can affect hormonal levels, and subsequently compromise performance and recovery. The aims of this project were to 1) assess the impact of an eight-day military training exercise on salivary cortisol and testosterone, 2) track the recovery of these hormones during a period of reduced training. Methods This was a prospective study whereby 30 soldiers (n = 27 men, n = 3 women) undergoing the Australian Army combat engineer ‘Initial Employment Training’ course were recruited and tracked over a 16-day study period which included an eight-day military training exercise. Non-stimulated saliva samples were collected at waking, 30 min post waking, and bedtime on days 1, 5, 9, 13, 15; measures of subjective load were collected on the same days. Sleep was measured continuously via actigraphy, across four sequential study periods; 1) baseline (PRE: days 1–4), 2) field training with total sleep deprivation (EX-FIELD: days 5–8), 3) training at simulated base camp with sleep restriction (EX-BASE: days 9–12), and 4) a three-day recovery period (REC: days 13–15). Results Morning cortisol concentrations were lower following EX-FIELD (p<0.05) compared to the end of REC. Training in the field diminished testosterone concentrations (p<0.05), but levels recovered within four days. Bedtime testosterone/cortisol ratios decreased following EX-FIELD and did not return to pre-training levels. Conclusions The sensitivity of testosterone levels and the testosterone/cortisol ratio to the period of field training suggests they may be useful indicators of a soldier’s state of physiological strain, or capacity, however inter-individual differences in response to a multi-stressor environment need to be considered.

Seasonal Variation in Vitamin D Status Does Not Interfere with Improvements in Aerobic and Muscular Endurance in Conscripts during Basic Military Training

“…Therefore, the monitoring of various hormonal markers can provide valuable information about the efficacy of the training process and the development of the trained state [48,49]. In a military environment, monitoring of serum testosterone and cortisol levels or TCR has been used for evaluation of training stress and for detecting too-heavy training loads which may lead to maladaptation [50][51][52][53]. In our conscripts, in both S-C and A-C, a significant increase in TCR over time suggests that they tolerated well the BMT-induced physical and psychological stress.…”

Characterising Psycho-Physiological Responses and Relationships during a Military Field Training Exercise

“…Data collection occurred as a part of a wider study which also examined hormonal responses [ 26 ] and changes in cognitive function [ 27 ] over this 15-day period within the Australian Army Combat Engineers Initial Employment Training course at Holsworthy Barracks, NSW, Australia. A conservative power analysis, using Heart Rate Variability (HRV), the ‘noisiest’ variable of interest, was undertaken as part of the wider study revealing a minimum sample size of 19 was required.…”