Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York.
Department of Kinesiology, School of Public Health, Indiana University, Bloomington, Indiana.
J Occup Environ Hyg. 2023 Sep;20(9):414-425. doi: 10.1080/15459624.2023.2221713. Epub 2023 Jul 6.
The impact of water consumption bolus volume and frequency on hydration biomarkers during work in the heat is unknown. In a randomized, crossover fashion, eight males consumed either 500 mL of water every 40 min or 237 mL of water every 20 min during 2 hr of continuous walking at 6.4 kph, 1.0% grade in a 34 °C/30% relative humidity environment, followed by 2 hr of rest. Hydration biomarkers and variables were assessed pre-work, post-work, and after the 2 hr recovery. There were no differences in body mass between trials at any time point (all > 0.05). Percent change in plasma volume during work was not different when 237 mL of water was repeatedly consumed (-1.6 ± 8.2%) compared to 500 mL of water (-1.3 ± 3.0%, = 0.92). Plasma osmolality was maintained over time ( = 0.55) with no difference between treatments ( = 0.21). When consuming 500 mL of water repeatedly, urine osmolality was lower at recovery (205 ± 108 mOsmo/L) compared to pre-work (589 ± 95 mOsmo/L, < 0.01), different from repeatedly consuming 237 mL of water which maintained urine osmolality from pre-work (548 ± 144 mOsmo/L) through recovery (364 ± 261 mOsmo/L, = 0.14). Free water clearance at recovery was greater with repeated consumption of 500 mL of water (1.2 ± 1.0 mL/min) compared to 237 mL of water (0.4 ± 0.8 mL/min, = 0.02). Urine volume was not different between treatments post-work ( = 0.62), but greater after 2 hr of recovery when repeatedly consuming 500 mL of water compared to 237 mL ( = 0.01), leading to greater hydration efficiency upon recovery with repeated consumption of 237 mL of water (68 ± 12%) compared to 500 mL (63 ± 14%, = 0.01). Thirst and total gastrointestinal symptom scores were not different between treatments at any time point (all > 0.05). Body temperatures and heart rate were not different between treatments at any time point (all > 0.05). Drinking larger, less frequent water boluses or drinking smaller, more frequent water boluses are both reasonable strategies to promote adequate hydration and limit changes in body mass in males completing heavy-intensity work in the heat.
水合生物标志物在热环境中工作时的水消耗量和频率的影响尚不清楚。在一项随机交叉试验中，8 名男性在 34°C/30%相对湿度环境中以 6.4 kph、1.0%坡度连续行走 2 小时，每隔 40 分钟饮用 500ml 水，或每隔 20 分钟饮用 237ml 水，之后进行 2 小时的休息。在工作前、工作后和 2 小时恢复后评估水合生物标志物和变量。在任何时间点，两次试验之间的体重均无差异（均>0.05）。当反复饮用 237ml 水时，工作期间血浆体积的百分比变化与饮用 500ml 水时相似（-1.6±3.0%，=0.92）。血浆渗透压随时间保持不变（=0.55），处理之间无差异（=0.21）。当反复饮用 500ml 水时，恢复时的尿液渗透压较低（205±108 mOsmo/L），与工作前相比（589±95 mOsmo/L，<0.01），而反复饮用 237ml 水时，尿液渗透压从工作前（548±144 mOsmo/L）到恢复时（364±261 mOsmo/L，=0.14）保持不变。恢复时重复饮用 500ml 水的自由水清除率较高（1.2±1.0 mL/min），而饮用 237ml 水的自由水清除率较低（0.4±0.8 mL/min，=0.02）。工作后，两种处理之间的尿液量没有差异（=0.62），但在 2 小时恢复后，反复饮用 500ml 水时的尿液量大于饮用 237ml 水时（=0.01），导致反复饮用 237ml 水时的水合效率更高（68±12%），而饮用 500ml 水时的水合效率更低（63±14%，=0.01）。在任何时间点，处理之间的口渴和总胃肠道症状评分均无差异（均>0.05）。在任何时间点，处理之间的体温和心率均无差异（均>0.05）。在热环境中进行高强度工作时，男性可选择饮用较大但频率较低的水合液或较小但频率较高的水合液，这两种策略均可促进充分水合并限制体重变化。
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