Heat strain during military training activities: The dilemma of balancing force protection and operational capability

Abstract

Military activities in hot environments pose 2 competing demands: the requirement to perform realistic training to develop operational capability with the necessity to protect armed forces personnel against heat-related illness. To ascertain whether work duration limits for protection against heat-related illness restrict military activities, this study examined the heat strain and risks of heat-related illness when conducting a military activity above the prescribed work duration limits. Thirty-seven soldiers conducted a march (10 km; ∼5.5 km h−1) carrying 41.8 ± 3.6 kg of equipment in 23.1 ± 1.8°C wet-bulb globe temperature. Body core temperature was recorded throughout and upon completion, or withdrawal, participants rated their severity of heat-related symptoms. Twenty-three soldiers completed the march in 107 ± 6.4 min (Completers); 9 were symptomatic for heat exhaustion, withdrawing after 71.6 ± 10.1 min (Symptomatic); and five were removed for body core temperature above 39.0°C (Hyperthermic) after 58.4 ± 4.5 min. Body core temperature was significantly higher in the Hyperthermic (39.03 ± 0.26°C), than Symptomatic (38.34 ± 0.44°C; P = 0.007) and Completers (37.94 ± 0.37°C; P<0.001) after 50 min. Heat-related symptom severity was significantly higher among Symptomatic (28.4 ± 11.8) compared to Completers (15.0 ± 9.8, P = 0.006) and Hyperthermic (13.0 ± 9.6, P = 0.029). The force protection provided by work duration limits may be preventing the majority of personnel from conducting activities in hot environments, thereby constraining a commander's mandate to develop an optimised military force. The dissociation between heat-related symptoms and body core temperature elevation suggests that the physiological mechanisms underpinning exhaustion during exertional heat stress should be re-examined to determine the most appropriate physiological criteria for prescribing work duration limits.

Systematic review of gender differences in the epidemiology and risk factors of exertional heat illness and heat tolerance in the armed forces

“…34 Furthermore, during military training exercises, men may have comparatively tolerated working in the heat beyond the endurance limits. 22 This finding was re-echoed in a previous systematic review that men in the general population had a higher rate of all types of heat illnesses compared with women. 21 Although the incidence of heat stroke was lower in women compared with men in this review, the incidence of heat stroke among women has increased over the past 4 years.…”

“…21 However, no previous review has investigated the epidemiology and risk factors of heat illness as well as gender responses to the heat tolerance test in men and women in the armed forces. Given that, heat illness can impact defence operational effectiveness and may result in acute loss of manpower and possible medical discharge from service, 22 the review should be conducted to inform policies.…”

Heat, health, and humidity in Australia's monsoon tropics: a critical review of the problematization of ‘heat’ in a changing climate

“… Such accounts have tended to focus not just on environmental conditions but also on exertion and exposure as areas of intervention. The Australian Defence Force for example articulates levels of exertion in relation to exposure through establishing recommended workload and work/rest cycles in relation to particular WBGT values . For other labor‐intensive industries, including those in the monsoon tropics, WHS policies follow a similar basic principle, typically recommending ‘work to rest ratios,’ ‘down tools policies,’ strategies to ‘self‐pace’ or otherwise reduce work intensity and strategies such as ‘rescheduling work so the hot tasks are performed during the cooler part of the day’ (see, e.g., Refs and ).…”

Interaction between Indoor Occupational Heat Stress and Environmental Temperature Elevations during Heat Waves

“…A recent systematic review and meta-analysis reported that during, or at the end of work under heat stress, 35% of workers experience occupational heat strain, while 30% of workers report productivity losses (Flouris et al 2018a). However, occupational heat stress has been mainly studied to date in jobs associated with the military, construction, mining, agricultural, and metal industries (Brake and Bates 2002;Hunt et al 2016;Jay and Brotherhood 2016;Krishnamurthy et al 2017;Ryan and Euler 2017), as they include intense physical activity, wearing of protective clothing, and/or exposure to extreme ambient conditions. For outdoor workers it is well documented that high environmental heat strain has marked negative effects on workers' productivity (Ioannou et al 2017;Sahu et al 2013), whereas the effects on indoor workers are less clear and the impact more complex as industrial heat production and building architecture become factors of importance.…”