Noakes Timothy D
Department of Human Biology, University of Cape Town, Sports Science Institute of South Africa, Cape Town, South Africa.
Sports Med. 2007;37(4-5):463-6. doi: 10.2165/00007256-200737040-00050.
Early human ancestors evolved hunting in the midday heat on the dry African savannah and developed favourable biological adaptations that permit prolonged running in the heat. These physiological adaptations must have included the capacity to sweat profusely to maintain a low body temperature when running for 4-6 hours in dry heat, an absence of adverse consequences from developing mild to moderate fluid deficits caused by sweat losses during the hunt, a serum osmolality based thirst mechanism and the ability to 'outrun their thirst' (to resist the deleterious psychological and other effects of severe thirst). Until the early 1970s, the guidelines for fluid ingestion during exercise were not to drink and are consistent with this interpretation. By 1996, guidelines stated, "individuals should be encouraged to consume the maximal amount of fluids during exercise that can be tolerated without gastrointestinal discomfort up to a rate equal to that lost from sweating," and this was interpreted by some as "to drink as much as tolerable." This article argues that humans are designed to drink just enough to maintain plasma osmolality, not necessarily bodyweight, both at rest and during exercise. Drinking to maintain bodyweight may impair exercise performance by inducing a weight penalty and may increase the probability of exercise-associated hyponatraemia in slow marathon runners.
早期人类祖先在炎热的非洲大草原中午时分进化出狩猎行为，并形成了有利的生物适应性，使其能够在高温下长时间奔跑。这些生理适应性必然包括在干燥炎热环境中奔跑4至6小时时大量出汗以维持低体温的能力、狩猎过程中因出汗导致轻度至中度体液不足而不会产生不良后果、基于血清渗透压的口渴机制以及“跑赢口渴”的能力（即抵抗严重口渴带来的有害心理和其他影响）。直到20世纪70年代初，运动期间的液体摄入指南都是不喝水，这与上述解释一致。到1996年，指南规定：“应鼓励个人在运动期间摄入能耐受且不会引起胃肠道不适的最大量液体，摄入量应与出汗量相当”，一些人将此解释为“能喝多少就喝多少”。本文认为，人类无论是在休息还是运动时，其生理设计都是饮用足以维持血浆渗透压的液体量，而不一定是维持体重的液体量。为维持体重而饮水可能会因增加体重负担而损害运动表现，并且可能会增加慢速马拉松跑者发生运动相关性低钠血症的概率。
