EFFECT OF BODY HYPOHYDRATION ON AEROBIC PERFORMANCE OF BOYS WHO EXERCISE IN THE HEAT

Abstract

PURPOSE: To assess the effect of various levels of body hypohydration on aerobic performance in boys. METHODS: Seven 10- to 12-year-old boys attended three sessions in which they first dehydrated through exercise (6×10-min bouts at 40–45% VO2max) in a climatic chamber, then rested for 45 min in a thermoneutral room and finally performed in 35°C, 50% relative humidity an all-out cycling test at 90% VO2max. Dehydration was aimed to induce hypohydration of 0%, 1% or 2% of initial body weight (BW). These were achieved through individualized combinations of climatic heat stress and drinking regimens. Session sequence was counterbalanced. BW changes, total work to exhaustion (TW) in kJ and heart rate (HR) were recorded. RESULTS: As intended, initial BW changes (−0.02 ± 0.02 %BW, −1.08 ± 0.06 %BW, −2.12 ± 0.05 %BW, for 0%, 1% and 2%, respectively) were significantly different (p < 0.001) among the sessions. TW was significantly lower −49.2 ± 10.0 kJ (p < 0.05) and 40.2 ± 7.8 kJ (p < 0.05) – in 1% and 2%, respectively, than in 0% (55.5 ± 11.3 kJ). HR at the end of the test reached a similar level (on average, 189–193 bpm, 95–98 %HRmax) in all sessions. CONCLUSION: Even mild (1%BW) to moderate (2%BW) hypohydration causes significant reduction in aerobic performance of boys at 35 °C, 50% relative humidity. Therefore, dehydration should be prevented to maintain performance in the heat. Supported by Gatorade Sports Science Institute