Vrijens D M, Rehrer N J
School of Physical Education, Otago University, Dunedin, New Zealand.
J Appl Physiol (1985). 1999 Jun;86(6):1847-51. doi: 10.1152/jappl.1999.86.6.1847.
This study assessed whether replacing sweat losses with sodium-free fluid can lower the plasma sodium concentration and thereby precipitate the development of hyponatremia. Ten male endurance athletes participated in one 1-h exercise pretrial to estimate fluid needs and two 3-h experimental trials on a cycle ergometer at 55% of maximum O2 consumption at 34 degrees C and 65% relative humidity. In the experimental trials, fluid loss was replaced by distilled water (W) or a sodium-containing (18 mmol/l) sports drink, Gatorade (G). Six subjects did not complete 3 h in trial W, and four did not complete 3 h in trial G. The rate of change in plasma sodium concentration in all subjects, regardless of exercise time completed, was greater with W than with G (-2.48 +/- 2.25 vs. -0.86 +/- 1.61 mmol. l-1. h-1, P = 0.0198). One subject developed hyponatremia (plasma sodium 128 mmol/l) at exhaustion (2.5 h) in the W trial. A decrease in sodium concentration was correlated with decreased exercise time (R = 0.674; P = 0.022). A lower rate of urine production correlated with a greater rate of sodium decrease (R = -0. 478; P = 0.0447). Sweat production was not significantly correlated with plasma sodium reduction. The results show that decreased plasma sodium concentration can result from replacement of sweat losses with plain W, when sweat losses are large, and can precipitate the development of hyponatremia, particularly in individuals who have a decreased urine production during exercise. Exercise performance is also reduced with a decrease in plasma sodium concentration. We, therefore, recommend consumption of a sodium-containing beverage to compensate for large sweat losses incurred during exercise.
本研究评估了用无钠液体补充汗液流失是否会降低血浆钠浓度，从而促使低钠血症的发生。十名男性耐力运动员参加了一次1小时的运动前测试以估计液体需求量，并在34摄氏度、相对湿度65%的条件下，以最大耗氧量的55%在自行车测力计上进行了两次3小时的实验性测试。在实验性测试中，液体流失分别用蒸馏水（W组）或含钠（18 mmol/l）的运动饮料佳得乐（G组）进行补充。六名受试者在W组测试中未完成3小时，四名受试者在G组测试中未完成3小时。无论完成的运动时间如何，所有受试者血浆钠浓度的变化率W组均大于G组（-2.48±2.25 vs. -0.86±1.61 mmol·l-1·h-1，P = 0.0198）。一名受试者在W组测试的疲劳期（2.5小时）出现了低钠血症（血浆钠128 mmol/l）。钠浓度的降低与运动时间的减少相关（R = 0.674；P = 0.022）。较低的尿量生成率与较大的钠降低率相关（R = -0.478；P = 0.0447）。汗液分泌量与血浆钠降低无显著相关性。结果表明，当汗液流失量大时，用纯水W补充汗液流失可导致血浆钠浓度降低，并可促使低钠血症的发生，尤其是在运动期间尿量减少的个体中。血浆钠浓度降低也会降低运动表现。因此，我们建议饮用含钠饮料以补偿运动期间大量的汗液流失。
