The University of Alabama, Tuscaloosa, AL Reliability of bioelectrical impedance spectroscopy after an acute exposure of passive heating Brett S. Nickerson, Bailey A. Welborn, Ronald L. Snarr, Mark Richardson, and Michael R. Esco The University of Alabama, Tuscaloosa, AL Abstract Methods Results Bioelectrical impedance spectroscopy (BIS) is a non-invasive method that is used for measuring body fat percentage (BF%) in various field settings. Events that might alter hydration status such as heat exposure may impact the reliability of BIS. However, there is limited information available to examine this statement. PURPOSE: The purpose of this study was to determine the impact of an acute exposure of passive heating on BIS-derived BF%. METHODS: Eighteen college-aged adult males partook in this study (age = 23.5 ± 3.6 years, height = 175.2 ± 6.1 cm, weight = 79.5 ± 11.2). Before testing all participants were required to be hydrated and provide a urine specific gravity < 1.020. Once hydration was confirmed participants had their first BF% value measured in a thermoneutral environment before (PRE) passive heating. Following the PRE trial, participants entered an environmental chamber and were instructed to lie supine on a gurney for 15 minutes at a temperature of 35° C. Following passive heating, the participants exited the environmental chamber back into a thermoneutral environment for a second (POST) BIS-derived BF% measurement. RESULTS: The mean (± SD) for PRE and POST BF% values were 17.9 ± 5.5% and 16.9 ± 5.5% respectively, which was significantly different (p < 0.001, Cohen’s d = 0.19). PRE had a near perfect intraclass correlation (ICC) with POST (ICC = 0.97). The 95% limits of agreement for BF% values ranged from -0.8% below to 2.9% above the mean difference of 1.05%. CONCLUSIONS: The results of this study found that PRE was significantly different than POST after an acute exposure to heat, though the effect size was trivial. The near perfect ICC and small range of individual differences suggest that the BIS differences were consistent for all individuals. PRACTICAL APPLICATOINS: Practitioners who utilize BIS in field settings during months of hot temperatures should consider the results of this study before the assessment of BF%. Hot environments may result in a slightly lower BIS-derived BF% value compared to when the measure is taken in a thermoneutral setting. Eighteen college-aged adults (age = 23.5 ± 3.6 years, height = 175.2 ± 6.1 cm, weight = 79.5 ± 11.2) volunteered to participate in this study. Prior to BIS 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 BIS 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) BIS-derived BF% measurement. BIS PRE – BIS POST (BIS PRE + BIS POST) / 2 Figure 2: Bland-Altman plot comparing the differences in PRE and POST BIS-derived BF% (n=18). 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 BIS POST BF% was significantly lower than PRE. Trivial difference in mean BF% before and after passive heat exposure. ICC suggests POST BIS-derived BF% is consistently lower than PRE. Narrow limits of agreement. Practical Applications Heat exposure induces a decrease in BF% when using BIS. Therefore, the device might be influenced in a field setting where temperature is not easily controlled. Practitioners utilizing BIS should recommend participants avoid hot temperatures since the condition could yield less reliable results than a thermoneutral environment. Results Intro & Purpose Body fat percentage (BF%) is often evaluated with field techniques such as bioelectrical impedance spectroscopy (BIS). Pretesting guidelines for BIS devices recommend the voidance of extreme temperatures before measurements. Research has shown hot temperatures to significantly influence single-frequency bioelectrical impedance analysis, but no information is available on the effects of acute heat exposure on BIS (1-3). The purpose of this study was to determine the impact of an acute exposure of passive heating on BIS- derived BF%. The mean (± SD) for PRE and POST BF% values were 17.9 ± 5.5% and 16.9 ± 5.5% respectively, which was significantly different (p < 0.001, Cohen’s d = 0.19). PRE had a near perfect intraclass correlation (ICC) with POST (ICC = 0.97). The 95% limits of agreement according to the Bland-Altman method for BF% values ranged from -0.8% below to 2.9% above the mean difference of 1.05%. 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.