Abstract
Simple SummaryThis study focuses on the biomarkers that are predictive of heat intolerance in military populations. Military personnel are at risk of exertional heat stroke when the body’s temperature increases during intense physical activity in hot weather. Exertional heat stroke (EHS) may accompany or precede heat intolerance, an unusual sensitivity to heat. However, it is unknown if blood biomarkers (haematological, biochemical and hormonal) are predictive of heat intolerance. We subjected a sample of Australian Defence Force personnel and civilian volunteers to a heat tolerance test (HTT), and blood samples were obtained pre-and post–HTT. The results showed that a history of EHS was associated with changes in creatinine and urea. The biochemical and hormonal biomarkers associated with heat intolerance were alanine amino transaminase, creatine kinase, cortisol and creatinine. Furthermore, creatinine and cortisol were identified as predictors and useful biomarkers of heat intolerance. This study also highlights the need for further exploration of genetic biomarkers to aid early identification and the return to duty process for military personnel who may be at risk of heat intolerance.Heat intolerance is the inability to withstand heat stress and this may occur due to exertional heat stroke (EHS). However, it is unknown if heat intolerance is associated with immune and hormonal disturbances. This study investigates haematological, biochemical and hormonal biomarkers related to heat intolerance and EHS in military and civilian volunteers. A quasi-experimental pre-and post-test design was used, with participants drawn from the Australian Defence Force (ADF) and the general populace. Blood samples were collected and analysed for biomarkers. Inferential statistics compared the biomarkers between the groups. Changes in alanine amino transaminase (p = 0.034), creatine kinase (0.044), cortisol (p = 0.041) and creatinine (p < 0.001) differed between the heat-intolerant and heat-tolerant groups. Participants with a history of EHS showed significant changes in creatinine (p = 0.022) and urea (p = 0.0031) compared to those without EHS history. Predictors of heat intolerance were increasing post-HTT creatinine and cortisol (OR = 1.177, p = 0.011 and OR = 1.015, p = 0.003 respectively). Conclusively, EHS history is associated with changes in creatinine and urea concentrations, while the predictors of heat intolerance are creatinine and cortisol. However, further exploration of other biomarkers, such as genetic polymorphism, is needed.
Highlights
Australia has experienced an increase in ambient temperature by 1 ◦ C since 1910, with heat waves projected to increase in the future [1]
When the predictive role of the biochemical biomarkers is assessed, the biomarkers found to be predictive of heat intolerance were creatinine and cortisol
Our study shows that dehydration is not predictive of heat intolerance; our participants were provided with water ad libitum throughout the exercise
Summary
Australia has experienced an increase in ambient temperature by 1 ◦ C since 1910, with heat waves projected to increase in the future [1]. The extreme heat conditions threaten the health and wellbeing of outdoor workers, including labourers, essential services workers, farmers, athletes and military personnel [2]. The military organisation responsible for defending Australian sovereignty and national interests is the Australian Defence Force (ADF) [3]. The physical activities performed by the ADF in regions characterised by extreme hot conditions increase the risk of exertional heat illness (EHI) [4]. EHI is a severity-based spectrum of disorders, and exertional heat stroke (EHS) is a severe form of EHI [5]. When EHS occurs, it is essential to determine if the personnel can return to duty [6]
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