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Objective: This project was aimed at evaluating the impact of combat armor on physiological and cognitive functions during low-intensity exercise in hot-humid conditions (36°C and 60% relative humidity). Methods: Nine males participated in three trials (2.5 hours), walking at two speeds and wearing different protective equipment: control (combat uniform and cloth hat); torso armor with uniform and cloth hat; and full armor (uniform, torso armor, and helmet). Results: As time progressed, core temperatures increased and deviated signifi cantly among trials, rising at 0.37°C h −1 (control), 0.41°C h −1 (torso armor), and 0.51°C h −1 (full armor). Heart rates also progressively diverged, and subjects lost signifi cantly more sweat during the two armored trials. However, cognitive-function tests revealed neither signifi cant main effects nor time by treatment interactions. Conclusion: The combat armor and helmet signifi cantly increased thermal and cardiovascular strain, but these were unlikely to lead to either exertional heat illness or impaired cognitive function during uneventful urban, military patrols in hot-humid conditions.

A significant number of military personnel suffer from exertional heat illness, with some extreme cases resulting in death. These illnesses may occur without warning, they are often characterised by a rapid onset and can occur even in experienced personnel. Various field treatments for hyperthermia have been developed, and one of particular interest is the use of cold-water immersion. Not surprisingly, immersion in ice-cold water (0-2oC) has been shown to be an effective means of rapidly reducing body core temperature (Proulx et al., 2003, 2006).

Extensive research into the physiological impact of wearing thermal protective clothing has been conducted for many years. However, the current literature does not provide a consensus concerning the interaction of heat strain and cognitive function. This project sought to investigate the problems associated with personnel working in uncompensable environmental conditions while wearing Australian Defence Force (ADF) protective clothing. Four separate investigations were conducted. The first was a field based study evaluating the thermal influences of operating a helicopter simulator. The second was a laboratory study evaluating the impact of wearing body armour on physiological and cognitive function. Thirdly, a theoretical evaluation of, the problems associated with performing work in an uncompensable heat stress environment and, the physical characteristics of various coolants and cooling systems were investigated. Finally, a laboratory investigation on the physiological and cognitive consequences of wearing a personal protective ensemble while performing exercise with and without an activated liquid-cooling garment. A significant reduction in flying performance was evident when pilots were heated to a mean skin temperature (TGsk) of~39EC compared to the other two conditions (~33EC and 37EC, P less than 0.05), using a water perfusion garment to achieve these target TGsk. However no obvious detriments in cognitive performancewere observed for the two laboratory based studies even though subjects were exposed to a significant thermal load, as determined by increases in TC, TGsk and fc (P less than 0.05). For the final study, where thermal strain was significantly higher in the hot-dry trial without cooling (P less than 0.05), resulting in a terminal rectal temperature that was 1.6EC higher than the thermoneutral condition, the liquid-cooling garment (water temperature 15EC) successfully prevented all detriments in physiological function observed during the hot-dry tr

The hottest months encountered on northern Australian cattle stations are from September to November, where the climate is both hot and dry, and it is during these months that horseback cattle mustering occurs. Stockmen wear clothing that restricts heat loss (collared shirts and long trousers), yet protective helmets have recently been introduced into the cattle industry (AS/NZS 3838:2006), as part of the increasing occupational health and safety responsibilities of pastoral companies. Anecdotal evidence points to the possibility that protective helmets may increase the probability of stockmen developing heat illness, or experiencing reduced workplace performance. Herein, we describe the working and thermal environment on these cattle stations, and provide an overview of the metabolic demands, and the concurrent physiological and cognitive strain encountered during horseback mustering in a hot-dry environment, whilst stockmen wore an equestrian helmet (Taylor and Caldwell, 2007). In subsequent investigations, we evaluated heat penetration through various forms of headwear (Caldwell and Taylor, 2007), and completed laboratory-based trials in which the physiological impact of an equestrian helmet, relative to the traditional felt hat, was evaluated (Caldwell et al., 2007).

The hand is one of the most closely studied body segments with respect to sweat secretion, with previous research focussing on its neural control, secretion differences between glabrous and non-glabrous (hairy) skin surfaces, and upon the impact of thermal and non-thermal stimuli on sudomotor function. It is generally considered that the glabrous palmar surfaces are adrenergically activated during times of mental or emotional stress, while the non-glabrous dorsal surfaces are cholinergically innervated, and respond to thermal stimuli (Wolf and Maibach, 1974). However, surprisingly little is known concerning the regional distribution of sweating within the palmar and dorsal surfaces of the hand. Therefore, in this project, we investigated the distribution of sweating within the hand, and measured sweat rates from ten sites on the dorsal and palmar surfaces during mild hyperthermia.

Metabolic and external heat sources are equally capable of elevating body core temperature in individuals working in hot environments. When heat loss avenues are impeded by clothing and protective equipment, the risk of exertional heat stress is further increased. There are various work-rest guidance tables available within the literature, some of these have correction factors for variations in clothing insulation, such that rest periods are lengthened and work periods shortened when clothing insulation is increased (TBMED 507). However, there is a paucity of experimental data upon which such modifications may be based. An absence of such empirical data may result either in an increased risk of exertional heat illness, or compromised operational capability, if physiological strain is over-estimated (Danielsson and Bergh, 2005). Therefore, the aim of this project was to assess the impact of wearing such body armour on physiological and cognitive function in hot-humid conditions.

When exposed to environmental heat stress, one’s ability to perform physical and mental tasks can be compromised. In relation to a helicopter pilot, a slight decrement in flight performance can result in devastating consequences. Previously, Froom et al. (1993) found environmental heat stress elevated pilot error, whilst Caldwell et al. (2005) have described impaired flight simulator performance during progressive hyperthermia. Such changes can reflect reduced cognitive function, and Faerevik and Reinertsen (2003) have shown that heat stress can contribute to deficits in both vigilance and multi-choice reaction time. Presumably, the use of biological and chemical (BC) protective clothing will exacerbate this state.

Within environments that pose either a chemical or a biological threat to workers, the ability to regulate body temperature is adversely affected by the need to wear personal protective ensembles. These chemical and biological (CB) protective ensembles impede the loss of metabolically-generated heat, the wicking of sweat and the removal of water vapour resulting from the evaporation of sweat. The design objective of most newly-developed materials is to facilitate heat loss, whilst retaining the appropriate chemical and biological protection. In this project, the focus was upon the physiological impact of exercising in a hot-dry environment, whilst wearing CB protective ensembles made from various combinations of these materials.

It is well known that elevations in body temperature can impair both physical and cognitive performance. For helicopter pilots, the major heat source during flight originates from solar radiation. However, when nuclear, biological and chemical (NBC) protective clothing is worn, metabolic heat generated during the pre-flight period, and during the mission, is trapped, exacerbating thermal strain. In this project, the hypothesis that elevations in body heat content would degrade flight performance was tested. Helicopter pilots completed three, two-hour flight simulations under three levels of thermal strain, administered in a balanced order. Thermal strain was induced using a water-perfusion gannent, worn under flight and NBC clothing, and supplied with water that would elicit skin temperatures of 33°C (control), 37°C (moderate) and 39°C (hot). Each sortie was programmed and controlled by the simulator flight officer (blind to treatment order), and was comprised of eight flight circuits, each involving takeoff and landing exercises. During each circuit, the pilots were required to identify and solve two operational problems, graded as "easy", "moderate" and "hard". In this report, we present preliminary data from four pilots. Terminal core temperatures for each trial were: 37.5°C (±0.17; control), 38.6°C (±0.14; moderate) and 38.8°C (±0.19; hot). This strain was also reflected within the terminal heart rates: 87.8 b.min-1 (±9.6; control), 127.8 b.min-1 (±9.1; moderate) and 150.8 b.min-1 (±6.1; hot). The simulator officer independently graded pilot performance, and while the moderate trial resulted in slightly reduced performance scores, relative to control (P>0.05), scores were significantly lower in the hot trials (P<0.05). Strong correlations existed between the thermal load and both the effort needed to sustain the appropriate flight performance, and the pilots' own assessment of performance quality. From these data, it appears that mean body temperature has the mo