Hypohydration and Hyperthermia Impair Neuromuscular Control after Exercise

Purpose: This study aimed to evaluate the effects of hypohydration and hyperthermia during exercise on movement technique and postural control. Methods: Twelve healthy men (age = 20 +/- 2 yr, height = 182 +/- 8 cm, mass = 74.0 +/- 8.2 kg, (V)over dotO(2max) = 57.0 +/- 6.0 mL.kg(-1).min(-1); mean +/- SD) completed four randomized test sessions: euhydrated temperate (EUT), euhydrated hot (EUH), hypohydrated temperate (HYT), and hypohydrated hot (HYH). Temperate and hot conditions were performed in 18.0 degrees C +/- 0.2 degrees C, 50.0% +/- 3.5% relative humidity, and 34.0 degrees C +/- 0.3 degrees C, 45.0% +/- 4.5% relative humidity, respectively. Movement technique and postural control were assessed before exercise (PRE), after exercise (POST), and after recovery (REC). Movement technique was evaluated using the Landing Error Scoring System (LESS). Postural control was assessed using the Balance Error Scoring System (BESS) and center-of-pressure sway velocity (SV) and elliptical sway area (ESA) during a dynamic balance test. The 90-min treadmill exercise protocol (1.34-1.78 m.s(-1); 5% grade) required subjects to walk carrying a 20.5-kg rucksack. Subjects sat quietly in the test environment during a 60-min recovery period after exercise. Repeated-measures ANOVAs with a Tukey-HSD post hoc test evaluated differences between time and condition for dependent variables. Results: Exercise during HYH significantly increased LESS scores (PRE = 3.72 +/- 1.73, POST = 4.42 +/- 1.75) compared with HYT (3.75 +/- 1.76) and EUH (3.61 +/- 1.71) (P < 0.05). LESS scores remained elevated during REC for HYH compared with EUT (4.39 +/- 1.47 vs 3.47 +/- 2.05, P < 0.05). The HYH condition caused the greatest number of BESS errors (P = 0.02), largest ESA (P < 0.05), and highest SV (P = 0.02). Regardless of the condition, participants had the most BESS errors (P = 0.002) and highest SV (P = 0.003) during POST compared with the PRE and REC. Conclusions: Hypohydration during exercise in the heat impairs neuromuscular control. These findings suggest that physical activity in the heat while dehydrated may affect parameters associated with a higher risk of injury.