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Introduction

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Whenever one’s body temperature rises, even for physiological reasons, we enter into danger and anything that interferes with physiological cooling, or adds to the internal heat load, exacerbates that danger. The wonder is, not that anyone gets hyperpyrexia, but that so few of us do.

Ladell WS Disorders due to heat. Trans R Soc Trop Med Hyg 1957;51:189–207

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Because sporting activity can occur in hot conditions, sports medicine clinicians must be well versed in both prevention and management of heat-associated illness. Humans can only survive core temperatures greater than 41°C (106°F) for short periods, and protein denatures at a body temperature of 45°C (113°F).

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Fortunately, of all mammals, humans have developed an almost unmatched capacity to sweat, providing our species with one of the greatest capacities to lose heat during exercise and thus safely regulate our body temperatures even during exercise of long duration in environmental conditions that would otherwise be considered extreme. This was brilliantly shown by the performance of the 40 kg Japanese runner, Mizuki Noguchi, who won the 2004 Athens Olympic Marathon for women in a time of 2 hr 26 min 20 sec despite the extreme environmental conditions—35°C with moderate humidity.

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Some have argued that this remarkable sweating capacity of humans must have developed for some evolutionary purpose. Thus, Heinrich has proposed that as humans are savanna-adapted animals, the reason for our highly developed sweating response is because it provides us with an advantage, most likely to perform prolonged exercise in the heat.1 According to Heinrich, “We don’t need a sweating response to outrun predators, because that requires relatively short, fast sprinting, where accumulating a heat load is, like a lactic acid load, acceptable. What we do need sweating for is to sustain running in the heat of the day—the time when most predators retire into the shade.”1 Heinrich also notes that modern hunter-gatherers, like the !Kung Bushmen (San) of Southern Africa, do not carry food or water with them (on 30 km hunts in the heat) because that “hinders their ability to travel.”1 The first documentation of just such a hunt recorded that the !Kung San do not begin these long hunts lasting 4–6 hours unless the desert temperature is in excess of 40°C (104°F) with low humidity;2 the preferred hunting temperature is 42–45°C (108–113°F). Recently, highly trained members of the South African Special Forces were able to race march over 25 km in a temperature of 43°C while fully clothed in battle dress carrying rifles and full packs without ill effect while drinking only according to the dictates of thirst.3

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Despite this remarkable ability of some humans to exercise in such heat without health risk, on occasion, heat injury, in particular heatstroke, occurs to persons exercising in much less severe environmental conditions when the total heat load cannot explain why heatstroke developed. This suggests that individual susceptibility, rather than ...

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