Physiological responses to hyperthermia during short term maximal exercise

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The effects of flame resistant protective clothing on heat exchange and thermal strain

Soldiers may be required to wear flame resistant protective clothing to mitigate the risk of burns in the event of a fire or exposure to flames. Flame resistance is provided by either including fibres of inherent flame resistance into the garments or by applying a flame retardant treatment to fibres that are usually flammable, which may affect the thermal properties of the clothing. The aim of this study was to evaluate the heat exchange properties of flame resistant protective clothing and predict the effects on thermal strain during prolonged work

Quantification of the decay and re-induction of heat acclimation in dry-heat following 12 and 26 days without exposure to heat stress

Compared with the induction of heat acclimation (HA), studies investigating the decay and re-induction of HA (RA) are relatively sparse and have yielded conflicting results. Therefore, 16 semi-nude men were acclimated to dry-heat by undertaking an exercise protocol in a hot chamber (dry-bulb temperature 46.1 ± 0.1°C; relative humidity 17.9 ± 0.1%) on 10 consecutive days (HA1-10) in winter UK. Thereafter, the subjects were divided into two groups and re-exposed to the work-in-heat tests after 12 and 26 days until RA was attained (RA12, n = 8; RA26, n = 8). The exercise protocol consisted of 60 min of treadmill walking (1.53 m s-1) at an incline individually set to induce a rectal temperature (Tre) of ∼38.5°C during HA1 (equating to 45 ± 4% peak oxygen uptake), followed by 10 min of rest and 40 min of further treadmill exercise, the intensity of which was increased across HA to maintain Treat ∼38.5°C. Tre, mean skin temperature, heart rate and rate of total water loss measured at 60 min did not change after HA7, and HA was taken as the mean of the responses during HA8-10. For both groups, there was no decay in Tre and for all measured variables RA was attained after 2 and 4 days in RA12 and RA26, respectively. It is concluded that once adaptation to heat has been attained, the time that individuals may spend in cooler conditions before returning to a hot environment could be as long as one month, without the need for extensive re-adaptation to heat

Sex-based differences in body core temperature response across repeat work bouts in the heat

Objective: To investigate the effects of repeated work bouts in the heat on peak body core temperature and to explore sex-based differences in body core temperature responses.Methods: Fourteen males and fifteen females performed four work bouts (two heavy and two moderate, alternating) in 32.5 °C Wet Bulb Globe Temperature (WBGT), each separated by 30-min seated rest in 28.0 °C WBGT. Participants wore a military combat uniform with body armour and helmet (10 kg load) during the work bouts, removing the vest and helmet during recovery periods.Results: Body core temperature elevation over time was faster in the first compared with subsequent work bouts of each intensity. Body core temperature elevation was similar between males and females during the first heavy work bout, then remained significantly lower in females for the reminder of the trial.Conclusions: Contrary to the assumed progressive elevation in strain, but in agreement with recent literature, a gradual reduction in heat storage in subsequent exercise bouts prevented a cumulative increase in heat strain in the conditions tested

Heat Stress Management in the Military: Wet-Bulb Globe Temperature Offsets for Modern Body Armor Systems

Objective: The aim of this study was to model the effect of body armor coverage on body core temperature elevation and wet-bulb globe temperature (WBGT) offset. Background: Heat stress is a critical factor influencing the health and safety of military populations. Work duration limits can be imposed to mitigate the risk of exertional heat illness and are derived based on the environmental conditions (WBGT). Traditionally a 3°C offset to WBGT is recommended when wearing body armor; however, modern body armor systems provide a range of coverage options, which may influence thermal strain imposed on the wearer. Method: The biophysical properties of four military clothing ensembles of increasing ballistic protection coverage were measured on a heated sweating manikin in accordance with standard international criteria. Body core temperature elevation during light, moderate, and heavy work was modeled in environmental conditions from 16°C to 34°C WBGT using the heat strain decision aid. Results: Increasing ballistic protection resulted in shorter work durations to reach a critical core temperature limit of 38.5°C. Environmental conditions, armor coverage, and work intensity had a significant influence on WBGT offset. Conclusion: Contrary to the traditional recommendation, the required WBGT offset was >3°C in temperate conditions (<27°C WBGT), particularly for moderate and heavy work. In contrast, a lower WBGT offset could be applied during light work and moderate work in low levels of coverage. Application: Correct WBGT offsets are important for enabling adequate risk management strategies for mitigating risks of exertional heat illness.</p

Influence of hydration volume and ambient temperature on physiological responses while wearing CBRN protective clothing

This study examined a low (L; 5 ml/kg per h) and high (H, 10 ml/kg per h) rate of fluid replacement in moderate (18°C) and hot (30°C) conditions on physiological responses while wearing personal protective equipment (PPE). PPE included the gas-tight suit (GTS), the powered respirator protective suit (PRPS) and the civil responder 1 (CR1). Relative to the moderate condition, physiological responses were greater in the hot condition. The percentage change in body mass was different (p 1% body mass loss and/or net body mass gain. STATEMENT OF RELEVANCE: Currently, the UK Emergency Services do not have specific evidence-based fluid replacement guidelines to follow when wearing chemical, biological, radiological and/or nuclear (CBRN) PPE. Although ad libitum fluid replacement is encouraged (when breathing apparatus permits), recommendations from evidence-based findings specific to different PPE and to different environmental conditions are lacking. This study provides novel evidence supporting the need to develop fluid replacement strategies during CBRN deployments in both moderate and hot environmental conditions for CBRN PPE

Health, fitness, and responses to military training of officer cadets in a Gulf Cooperation Council country.

To quantify the health, fitness, and physiological responses to military training of Officer Cadets from a Gulf Cooperation Council country