Rehrer N J
School of Physical Education and Department of Human Nutrition, Otago University, Dunedin, New Zealand.
Sports Med. 2001;31(10):701-15. doi: 10.2165/00007256-200131100-00001.
It is well known that fluid and electrolyte balance are critical to optimal exercise performance and, moreover, health maintenance. Most research conducted on extreme sporting endeavour (>3 hours) is based on case studies and studies involving small numbers of individuals. Ultra-endurance sportsmen and women typically do not meet their fluid needs during exercise. However, successful athletes exercising over several consecutive days come close to meeting fluid needs. It is important to try to account for all factors influencing bodyweight changes, in addition to fluid loss, and all sources of water input. Increasing ambient temperature and humidity can increase the rate of sweating by up to approximately 1 L/h. Depending on individual variation, exercise type and particularly intensity, sweat rates can vary from extremely low values to more than 3 L/h. Over-hydration, although not frequently observed, can also present problems, as can inappropriate fluid composition. Over-hydrating or meeting fluid needs during very long-lasting exercise in the heat with low or negligible sodium intake can result in reduced performance and, not infrequently, hyponatraemia. Thus, with large rates of fluid ingestion, even measured just to meet fluid needs, sodium intake is vital and an increased beverage concentration [30 to 50 mmol/L (1.7 to 2.9 g NaCl/L) may be beneficial. If insufficient fluids are taken during exercise, sodium is necessary in the recovery period to reduce the urinary output and increase the rate of restoration of fluid balance. Carbohydrate inclusion in a beverage can affect the net rate of water assimilation and is also important to supplement endogenous reserves as a substrate for exercising muscles during ultra-endurance activity. To enhance water absorption, glucose and/or glucose-containing carbohydrates (e.g. sucrose, maltose) at concentrations of 3 to 5% weight/volume are recommended. Carbohydrate concentrations above this may be advantageous in terms of glucose oxidation and maintaining exercise intensity, but will be of no added advantage and, if hyperosmotic, will actually reduce the net rate of water absorption. The rate of fluid loss may exceed the capacity of the gastrointestinal tract to assimilate fluids. Gastric emptying, in particular, may be below the rate of fluid loss, and therefore, individual tolerance may dictate the maximum rate of fluid intake. There is large individual variation in gastric emptying rate and tolerance to larger volumes. Training to drink during exercise is recommended and may enhance tolerance.
众所周知，体液和电解质平衡对于最佳运动表现乃至健康维持都至关重要。大多数针对极限体育活动（超过3小时）开展的研究都基于案例分析以及涉及少数个体的研究。超耐力运动员在运动过程中通常无法满足其体液需求。然而，连续运动数天的成功运动员则接近能够满足体液需求。除了体液流失外，尝试考虑所有影响体重变化的因素以及所有水的摄入来源很重要。环境温度和湿度的升高可使出汗率增加至约1升/小时。根据个体差异、运动类型尤其是强度的不同，出汗率可从极低值变化至超过3升/小时。尽管不常出现，但饮水过量也可能带来问题，不合适的液体成分同样如此。在炎热环境下进行长时间运动且钠摄入量低或可忽略不计时，饮水过量或满足体液需求可能会导致运动表现下降，且低钠血症也并不罕见。因此，即便大量饮水只是为了满足体液需求，钠的摄入也至关重要，增加饮料浓度[30至50毫摩尔/升（1.7至2.9克氯化钠/升）]可能有益。如果运动期间饮水不足，恢复期补充钠对于减少尿量以及提高体液平衡恢复速率是必要的。饮料中添加碳水化合物会影响水的净同化率，在超耐力活动期间作为运动肌肉的底物补充内源性储备也很重要。为提高水的吸收，建议使用浓度为3%至5%重量/体积的葡萄糖和/或含葡萄糖的碳水化合物（如蔗糖、麦芽糖）。高于此浓度的碳水化合物在葡萄糖氧化和维持运动强度方面可能具有优势，但不会带来额外益处，而且如果是高渗的，实际上会降低水的净吸收速率。体液流失速率可能超过胃肠道吸收液体的能力。尤其是胃排空速率可能低于体液流失速率，因此，个体耐受性可能决定液体摄入的最大速率。胃排空速率和对大量液体的耐受性存在很大个体差异。建议进行运动期间饮水训练，这可能会提高耐受性。
