Date of Completion

5-7-2011

Embargo Period

4-26-2011

Open Access

Open Access

Abstract

ABSTRACT

Individual and Combined Effects of Hyperthermia, Dehydration and Fatigue on Balance. Megan M. VanSumeren, University of Connecticut

Purpose: The purpose of this controlled, randomized laboratory study was to determine the effect of hyperthermia, dehydration and fatigue as both combined and individual factors on balance performance as tested with three separate balance assessment tools.

Methods: 12 healthy male subjects (20±2 yrs old, 181.83±7.53cm , 74.09±8.43kg) completed four trials in a randomized order. The four trials were Normothermic, Hydrated (HyN), Normothermic Dehydrated (DehyN), Hyperthermic, Hydrated (HyHot), and Hyperthermic, Dehydrated (DehyHot). Balance was assessed using three tests; static stance, clinical tool Balance Error Scoring System (BESS), and a dynamic stance. Subjects performed the balance assessments three times during each trial; before exercise (pre-test), immediately after exercise (post-test) and after an hour of recovery (rec). The exercise component required subjects to walk on a 5% incline treadmill for 90 minutes at a pre-determined speed between 3.0mph-4.0mph. During the recovery period, subjects sat in the heat chamber with a water perfused suit on in order to maintain their exercising rectal temperature. Subjects were required to wear a 20.45kg pack during the entirety of the trial with the exception of the seated recovery period. Dependent variables were: center of pressure (COP), mean sway velocity, mean COP sway path, and average elliptical sway area for both the static and dynamic tests, as well as BESS individual stance scores and BESS total score. Separate repeated measures analyses of variance were performed to evaluate the dependent variables between time (pre-post-rec) and trials (HyN, DehyN, HyHot, DehyHot).

Results: For the BESS test, a main effect for time was observed for three of the four stances; SLFirm (F(2,22)=5.37, p=.01), TanFirm (F(2,22)=4.64, p=.02), TanFoam (F(2,22)=3.44, p=.05). The post-test held the highest number of errors on any stance compared with the pre-test and the recovery test. Both the TanFirm and TanFoam revealed a main effect for condition (F(3,33)=3.05, p=.04, F(3,33)=7.14, p=.001, respectively). Overall, the DehyHot condition caused the highest BESS scores. For the Dynamic stance, a main effect for time was noticed for the variables of mean COP sway path and velocity (F(2,22)=7.60 , p=.003, F(2,22)=7.61, p=.003, respectively) with the post-test resulting in the longest and fastest measures. All three variables demonstrated a main effect for condition; sway area (F(1.93, 21.26)=3.56, p=.048), sway path (F(3.33)=3.39, p=.029), velocity (F(3,33)=3.58, p=.024). The DehyHot trial caused the biggest changes in postural sway. Static results revealed a main effect for time in sway path and sway velocity (F(2,22)=4.03, p=.032, F(91.2, 13.5)=5.56, p=.045, respectively). Post-test scores caused the biggest change in sway.

Conclusions: For all three of the balance assessments, there was a decrease in balance ability at post-test. The highest values on any balance assessment took place in the DehyHot trial, suggesting that when combined, dehydration and hyperthermia affect balance. Overall, balance deficits were driven mostly by fatigue in the dehydrated and hyperthermic condition.

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