Voluntary fluid intake, hydration status, and aerobic performance of adolescent athletes in the heat
 
 
Journal Title (Medline/Pubmed accepted abbreviation): Appl Physiol Nutr Metab
Year: 2010
Volume: 35
Number: 6
Page numbers: 834-841
doi: 10.1139/H10-084

Summary of Background and Research Design

Background: Exercising in higher temperatures can lead to dehydration if voluntary fluid intake does not adequately compensate for fluid loss. The composition, flavor, and temperature of a drink influences fluid consumption. In several studies, dehydration was prevented in highly trained and heat-acclimated boys with availability of flavored, carbohydrate-added water. However, few studies in child athletes evaluating voluntary fluid intake and body fluid balance are reflective of real training or race conditions. Therefore, this study was undertaken to assess the effects of drink flavoring and composition on fluid intake, hydration, and performance in adolescent male runners exercising in the heat.

Hypothesis/purpose of study:It was hypothesized that both flavoring and addition of carbohydrates and electrolytes to drinks would increase voluntary fluid consumption, thereby preventing dehydration and increasing exercise performance during a running exercise at higher temperatures.

Subjects:8 self-reported healthy males who ran cross country volunteered for this study (mean ± standard deviation: age, 13.7 ± 1.1 yr; height, 165.3 ± 8.5 cm; weight, 51.6 ± 8.5 kg; percent body fat, 13.2% ± 5.4%; VO2peak, 59.5 ± 4.0 mL O2/kg/minute)

Experimental design:Repeated-measures, cross-over study

Treatments and protocol: 8 treadmill sessions were conducted over 5 to 6 weeks (orientation, 4 identical heat-acclimation sessions, and 3 identical exercise sessions). Orientation included a beverage sensory test. Testing was 110 minutes (5 bouts of 15-minute running and 5 minutes of rest in-between), followed by a 10-minute rest and running to exhaustion (90% VO2peak). A chilled beverage was available at all times during the testing session only and was consumed ad libitum by the subjects. The chilled beverage was tap water, grape-flavored water (FW), or grape-flavored water with 6% carbohydrate and 18 mmol/L sodium chloride added (CNa). Body weight (including clothes), temperature, VO2, and heart rate were recorded at baseline, at the end of exercise and rest periods, and during the last run. Dehydration was calculated as percent change in body weight adjusted for urine output and clothing weight (sweat).

Summary of research findings:
  • Although the athletes could detect differences in taste and sweetness between tap water and the supplemented drinks, they could not detect a difference between the FW and CNa.
  • Heart rate, temperature, and perceived exertion were similar for all 3 beverage sessions.
    • – No beverage × time interaction effects were found.
No beverage × time interaction effects were found.
  • Voluntary fluid intake was 77%, 74%, and 93% of total fluid lost during the exercise session for water, FW, and CNa, respectively.
    • –This intake was sufficient to compensate for 90%, 94%, and 112%, respectively, of sweat losses alone (no significant differences among the beverages).
  • Time to exhaustion was not significantly different between water, FW, and CNa sessions (8.7, 7.8, and 9.7 min, respectively; P = .16).
  • There was no significant correlation between percent body weight change and time to exhaustion.

Interpretation of findings/Key practice applications:

Flavored water with or without additives did not significantly stimulate fluid intake in this study, which reflected real-life conditions. These findings are in contrast to previous studies, where conditions may not reflect actual training or nonathletes were evaluated. There was also no effect from FW and CNa on exercise performance compared with tap water, although this should not be unexpected considering the adequate fluid intake of the volunteers. Based on these data, heat-acclimated adolescent males can voluntarily consume enough of any fluid to remain well hydrated and maintain performance while exercising in the heat.
 
However, this study had limitations that may have resulted in the lack of beverage effect on fluid intake. The athletes in this study may have been more knowledgeable concerning hydration and its importance. In addition, the exercise duration may have been too short. In a previous similar study, it took 90 minutes before differences in fluid balance became apparent. Finally, the potential effects of water additives on thirst may have been too small to influence fluid intake in this study because the intensive exercise levels may have created a high demand for fluids that overwhelmed any preference to satisfy thirst.
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