Martin D Hoffman1,2,3, Rhiannon M J Snipe4,5, Ricardo J S Costa4. 1. Physical Medicine and Rehabilitation Service, Department of Veterans Affairs, Northern California Health Care System, 10535 Hospital Way, Sacramento, CA, 95655-1200, USA. mdhoffman@ucdavis.edu. 2. Department of Physical Medicine and Rehabilitation, University of California Davis Medical Center, Sacramento, CA, USA. mdhoffman@ucdavis.edu. 3. Ultra Sports Science Foundation, El Dorado Hills, USA. mdhoffman@ucdavis.edu. 4. Department of Nutrition, Dietetics and Food, Monash University, Victoria, Australia. 5. Centre for Sport Research, School of Exercise and Nutrition Sciences, Deakin University, Victoria, Australia.
Abstract
PURPOSE: To examine if ad libitum drinking will adequately support hydration during exertional heat stress. METHODS: Ten endurance-trained runners ran for 2 h at 60% of maximum oxygen uptake under different conditions. Participants drank water ad libitum during separate trials at mean ambient temperatures of 22 °C, 30 °C and 35 °C. Participants also completed three trials at a mean ambient temperature of 35 °C while drinking water ad libitum in all trials, and with consumption of programmed glucose or whey protein hydrolysate solutions to maintain euhydration in two of these trials. Heart rate, oxygen uptake, rectal temperature, perceived effort, and thermal sensation were monitored, and nude body mass, hemoglobin, hematocrit, and plasma osmolality were measured before and after exercise. Water and mass balance equations were used to calculate hydration-related variables. RESULTS: Participants adjusted their ad libitum water intake so that the same decrease in body mass (1.1-1.2 kg) and same decrease in body water (0.8-0.9 kg) were observed across the range of ambient temperatures which yielded significant differences (p < .001) in sweat loss. Overall, water intake and total water gain replaced 57% and 66% of the water loss, respectively. The loss in body mass and body water associated with ad libitum drinking resulted in no alteration in physiological and psychophysiological variables compared with the condition when hydration was nearly fully maintained (0.3 L body water deficit) relative to pre-exercise status from programmed drinking. CONCLUSIONS: Ad libitum drinking is an appropriate strategy for supporting hydration during running for 2 h duration under hot conditions.
PURPOSE: To examine if ad libitum drinking will adequately support hydration during exertional heat stress. METHODS: Ten endurance-trained runners ran for 2 h at 60% of maximum oxygen uptake under different conditions. Participants drank water ad libitum during separate trials at mean ambient temperatures of 22 °C, 30 °C and 35 °C. Participants also completed three trials at a mean ambient temperature of 35 °C while drinking water ad libitum in all trials, and with consumption of programmed glucose or whey protein hydrolysate solutions to maintain euhydration in two of these trials. Heart rate, oxygen uptake, rectal temperature, perceived effort, and thermal sensation were monitored, and nude body mass, hemoglobin, hematocrit, and plasma osmolality were measured before and after exercise. Water and mass balance equations were used to calculate hydration-related variables. RESULTS:Participants adjusted their ad libitum water intake so that the same decrease in body mass (1.1-1.2 kg) and same decrease in body water (0.8-0.9 kg) were observed across the range of ambient temperatures which yielded significant differences (p < .001) in sweat loss. Overall, water intake and total water gain replaced 57% and 66% of the water loss, respectively. The loss in body mass and body water associated with ad libitum drinking resulted in no alteration in physiological and psychophysiological variables compared with the condition when hydration was nearly fully maintained (0.3 L body water deficit) relative to pre-exercise status from programmed drinking. CONCLUSIONS: Ad libitum drinking is an appropriate strategy for supporting hydration during running for 2 h duration under hot conditions.
Authors: Rhiannon M J Snipe; Anthony Khoo; Cecilia M Kitic; Peter R Gibson; Ricardo J S Costa Journal: Eur J Appl Physiol Date: 2017-12-12 Impact factor: 3.078
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