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Abstract
Introduction Measuring cortisol during military training offers insights into physiological responses to stress. We attempted precisely timed, cortisol awakening response (CAR) and pre-sleep cortisol (PSC), and diurnal slope (peak morning minus evening cortisol), during a British Army exercise. We aimed to understand cortisol dynamics and evaluate the feasibility of CAR and PSC in this environment.
Method Setting: high-intensity, 10-day infantry exercise. Participants: regular infantry soldiers exercising (EX, n=25) or headquarters-based (HQ, n=6). Participants undertook PSC and WAKE and WAKE+30 min samples after 1–2 days, 5–6 days and 9–10 days. Wrist-worn GENEActiv accelerometers were used to assess sleep duration in EX only. Samples taken ±15 min from prespecified time points were deemed adherent. Validated questionnaires were used to measure resilience and perceived stress. Cortisol and cortisone were measured simultaneously by liquid chromatography tandem mass spectrometry.
Results From adherent participants’ samples, CAR was positive and tended to decrease as the exercise progressed. From all available data, HQ demonstrated greater diurnal slope than EX (F=7.68, p=0.02), reflecting higher morning cortisol (F=4.72, p=0.038) and lower PSC (p=0.04). No differences were seen in cortisol:cortisone ratio. 26.1% of CAR samples were adherent, with moderately strong associations between adherence and stress (r=0.41, p=0.009) but no association between adherence and day of exercise (χ2=0.27, p=0.8), sleep duration (r=–0.112, p=0.43) or resilience (r=–0.79, p=0.75). Test–retest reliability ratings for CAR were Cronbach’s α of 0.48, –11.7 and 0.34 for the beginning, middle and end of the exercise, respectively.
Conclusions We observed a reduction in morning cortisol and decreased diurnal slope during a high-intensity military exercise, compared with the HQ comparator cohort in whom diurnal slope was preserved. A carefully timed CAR was not feasible in this setting.
- DIABETES & ENDOCRINOLOGY
- Adrenal disorders
- Biochemistry
- General endocrinology
Data availability statement
Data are available upon reasonable request.
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Data availability statement
Data are available upon reasonable request.
Footnotes
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Contributors RMG, DW and RR conceived the study. RMG designed the protocol and obtained funding and ethical approval. RMG, NT, AC and JS edited the protocol and conducted the study. ITP and MS provided military perspective to study conduct and editorial input. NH and AT designed and conducted analyses. RMG produced the first draft and all authors wrote the manuscript. RMG is the guarantor and accepts full responsibility for the work and conduct of the study.
Funding This study was funded by a grant from the UK Ministry of Defence (ASC Task 0108).
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
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