Movement Technique and Standing Balance After Graded Exercise-Induced Dehydration

Context: Hypohydration has been shown to alter neuromuscular function. However, the longevity of these impairments remains unclear. Objective: To examine the effects of graded exercise-induced dehydration on neuromuscular control 24 hours after exercise-induced hypohydration. Design: Crossover study. Setting: Laboratory. Patients or Other Participants: A total of 23 men (age = 21 +/- 2 years, height = 179.8 +/- 6.4 cm, mass = 75.24 +/- 7.93 kg, maximal oxygen uptake [VO(2)max] = 51.7 +/- 5.5 mL.kg(-1).min(-1), body fat = 14.2% +/- 4.6%). Intervention(s): Participants completed 3 randomized exercise trials: euhydrated arrival plus fluid replacement (EUR), euhydrated arrival plus no fluid (EUD), and hypohydrated arrival plus no fluid (HYD) in hot conditions (ambient temperature = 35.2 degrees C +/- 0.6 degrees C, relative humidity = 31.3% +/- 2.5%). Each trial consisted of 180 minutes of exercise (six 30-minute cycles: 8 minutes at 40% VO(2)max; 8 minutes, 60% VO(2)max; 8 minutes, 40% VO(2)max; 6 minutes, passive rest) followed by 60 minutes of passive recovery. Main Outcome Measure(s): We used the Landing Error Scoring System and Balance Error Scoring System (BESS) to measure movement technique and postural control at pre-exercise, postexercise and passive rest (POSTEX), and 24 hours postexercise (POST24). Differences were assessed using separate mixed-design (trial x time) repeated-measures analyses of variance. Results: The magnitude of hypohydration at POSTEX was different among EUR, EUD, and HYD trials (0.2% +/- 1%, 3.5% +/- 1%, and 5% +/- 0.9%, respectively; P<.05). We observed no differences in Landing Error Scoring System scores at pre-exercise (2.9 +/- 1.6, 3.0 +/- 2.1, 3.0 +/- 2.0), POSTEX (3.3 +/- 1.5, 3.0 +/- 2.0, 3.1 +/- 1.9), or POST24 (3.3 +/- 1.9, 3.2 +/- 1.4, 3.3 +/- 1.6) among the EUD, EUR, and HYD trials, respectively (P =.90). Hydration status did not affect BESS scores (P =.11), but BESS scores at POSTEX (10.4 +/- 1.1) were greater than at POST24 (7.7 +/- 0.9; P =.03). Conclusions: Whereas exercise-induced dehydration up to 5% body mass did not impair movement technique or postural control 24 hours after a prolonged bout of exercise in a hot environment, postural control was impaired at 60 minutes after prolonged exercise in the heat. Consideration of the length of recovery time between bouts of exercise in hot environments is warranted.