Voluntary Fluid Intake And Core Temperature Responses In Children During Exercise In The Heat

Abstract

Hydration can play an important role in maintaining performance and reducing clinical risk related to heat strain in young athletes. However, there remain a limited number of studies that describe core body temperature and other related responses to voluntary fluid intake in children during exercise in the heat. PURPOSE To examine the effects of ad libitum fluid intake, using chilled (∼10°C) water (W) vs. an 8% carbohydrate-electrolyte ([Na+]: 11.8 mmol·l−1) solution (CHO-8%), on core temperature and other physiological, behavioral, and perceptual responses in children during exercise in a hot environment. METHODS 29 healthy, active children (14 boys, 15 girls; age: 11.4 ± 1.2 y, 9–12 y; height: 151.4 ± 7.8 cm; weight: 42.4 ± 6.6 kg; BMI: 18.4 ± 1.7) completed two 80-min intermittent exercise (treadmill: 70% VO2max; cycle ergometer: 60% VO2max) sessions (using W or CHO-8%) on separate days (randomized, crossover design) in a hot (33°C) and humid (relative humidity: 54.7 ± 3.8%) environment. During each exercise session, fluid intake, urine volume, body weight (BW), core temperature, heart rate (HR), perceived exertion (RPE), thirst, taste, and gastrointestinal discomfort were measured at selected time points. Pre- and post-exercise urine specific gravity and osmolality were also determined. RESULTS CHO-8% consumption was greater compared to W (838.5 ± 50.7 g vs. 560.4 ± 47.9 g; p < 0.0001). Accordingly, with a similar post-exercise urine output (CHO-8%: 75.0 ± 12.7 g; W: 88.5 ± 13.5 g; p=0.3358), there was greater fluid retention during exercise in the CHO-8% trial compared to W (763.5 ± 49.0 g vs. 471.9 ± 49.6 g; p < 0.0001). Estimated sweat loss (by BW) was similar in both trials (CHO-8%: 591.8 ± 22.6 g; W: 568.8 ± 25.2 g; p=0.2634), resulting in a positive BW change (adjusted for urine output) in the CHO-8% trial and a BW-indicated fluid deficit in the W trial (+171.7 ± 56.4 g vs. −106.4 ± 52.6 g; p=0.0001). Core temperature was slightly higher (0.16 ± 0.01°C; p=0.0125) during CHO-8%, though the rate of change was similar in both trials. Moreover, this subtle difference did not translate into any statistical difference in physiological stress between trials, as indicated by HR or RPE. CHO-8% was consistently preferred over W (p < 0.001) in all selected taste perception categories. CONCLUSION CHO-8% appears more effective than W in keeping healthy, active children hydrated, by encouraging greater fluid intake and maintaining body weight, during exercise in the heat. However, greater consumption and retention of CHO-8% did not provide any measurable thermoregulatory or perceived exertion advantages over W during this exercise protocol. Supported by Kraft Foods Global, Inc.