The University of Alabama, Tuscaloosa, AL RELIABILITY OF HAND-TO-FOOT BIOELECTRICAL IMPEDANCE AFTER AN ACUTE PERIOD OF PASSIVE HEATING Anthony W. Fava, Brett S. Nickerson, Bailey A. Welborn, Mark Richardson, and Michael R. Esco The University of Alabama, Tuscaloosa, AL Abstract Methods Results Bioelectrical impedance analysis (BIA) is a field method commonly used by practitioners for the estimation of body fat percentage (BF%).  Many requirements must be met prior to administration such as avoiding extreme temperatures.  However, there is limited information available investigating the effects of hot temperatures on BIA.  PURPOSE: The purpose of this study was to determine the influence of an acute exposure of passive heating on BIA-derived BF%.  METHODS: Nineteen apparently healthy college-aged males participated in this study (age = 23.3 ± 3.6 years, height = 175.5 ± 6.1 cm, weight = 79.5 ± 10.8 kg).  Prior to participation all participants were required to provide a urine specific gravity (USG) less than 1.020. Upon ensuring USG was less than 1.020, BIA-derived BF% measures were performed in a thermoneutral environment before (PRE) passive heating. Following PRE condition, participants entered an environmental chamber and were instructed to lie supine on a gurney for 15 minutes at a temperature of 35° C. Immediately after 15 minutes of passive heating, the participants exited the environmental chamber and returned to a thermoneutral environment for a second BF% measurement (POST).  RESULTS: The mean (± SD) for PRE and POST BIA-derived BF% was 22.6 ± 3.8% and 21.1 ± 4.0% respectively, which was significantly different (p < 0.001, Cohen’s d = 0.40).  PRE had a near perfect intraclass correlation (ICC) with POST (ICC = 0.92).  The method of Bland-Altman showed 95% limits of agreement for BF% values to range from 0.5% below to 2.7% above the mean difference of 1.5%. CONCLUSIONS: The findings of this investigation showed that PRE provided a slightly higher BF% value than POST after an acute exposure to heat.  Furthermore, the near perfect ICC in addition small limits of agreement suggest that there was similar patterns of variability between the PRE and POST BF% values. PRACTICAL APPLICATIONS: Practitioners who utilize BIA in settings that are hot or where temperature is not easily controlled should consider the results of this study prior to assessing BF%.  An acute exposure of passive heating results in a slightly lower BF% value when compared to measures that are taken in a controlled setting such as a thermoneutral environment, which could influence the reliability of the device.   Nineteen college-aged adults (age = 23.3 ± 3.6 years, height = 175.5 ± 6.1 cm, weight = 79.5 ± 10.8) volunteered to participate in this study. Prior to BIA measurements, all participants were required to be hydrated and provide a urine specific gravity < 1.020. After hydration was confirmed, the first BF% value was measured in a thermoneutral (22° C) environment before (PRE) an acute period of passive heating. Following PRE BIA measures, participants were instructed to lie supine on a gurney in an environmental chamber for 15 minutes at a temperature of 35° C. After the acute period of passive heating, participants exited the environmental chamber back into a thermoneutral environment for a second (POST) BIA-derived BF% measurement. BIA PRE – BIA POST (BIA PRE + BIA POST) / 2 Figure 2: Bland-Altman plot comparing the differences in PRE and POST BIA-derived BF% (n=19). The middle solid line indicates the constant error between PRE and POST values. The 2 outside dashed lines indicate the 95% confidence interval of the difference. Conclusions POST BIA-Derived BF% was significantly lower than PRE, but had a small effect size. POST BIA-derived BF% is consistently lower than PRE. Narrow limits of agreement for PRE and POST BF%. Practical Applications Heat exposure results in a decreased BF% value when using hand-to-foot BIA. Therefore, the device should not be used for analysis on individuals who are exposed to hot temperatures prior to testing. Practitioners utilizing hand-to-foot BIA should recommend participants avoid hot environments since it might result in less reliability of the device. Results Intro & Purpose The mean (± SD) for PRE and POST BF% values were 22.6 ± 3.8% and 21.1 ± 4.0% respectively, being significantly different (p < 0.001, Cohen’s d = 0.19). PRE had a near perfect intraclass correlation (ICC) with POST (ICC = 0.92). The 95% limits of agreement according to the Bland-Altman method for BF% values ranged from 0.5% below to 2.7% above the mean difference of 1.5%. Hand-to-foot bioelectrical impedance is used to estimate body fat percentage (BF%). Pretesting guidelines for BIA devices recommend the avoidance of extreme temperatures before measurements. There is limited information available investigating the effects of hot temperatures on BIA. The purpose of this study was to determine the impact of an acute exposure of passive heating on hand- to foot BIA-derived BF%. References Buono MJ, Burke S, Endemann S, Graham H, Gressard C, Griswold L, and Michalewicz B. The effect of ambient air temperature on whole-body bioelectrical impedance. Physiological Measurement 25: 119-123, 2004 Caton JR, Molé PA, Adams WC, and Heustis DS. Body composition analysis by bioelectrical impedance: effect of skin temperature. Medicine and Science in Sports and Exercise 20: 489-491, 1988. Liang MT, Su HF, and Lee NY. Skin temperature and skin blood flow affect bioelectric impedance study of female fat-free mass. Medicine and Science in Sports and Exercise 32: 221-227, 2000.