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THE EFFECT OF PRETEST INSTRUCTIONS AND BETWEEN DAY TEST-RETEST RELIABILITY OF AIR DISPLACEMENT PLETHYSMOGRAPHY

Abstract

E. Dunston, S. Chriest, S. Avena, K. Taylor, A. Vahk

Eastern Washington University, Cheney, WA

Air displacement plethysmography (ADP) is considered a valid estimate of body composition. However, pretest instructions are often not followed by the general population which is imperative for tracking body composition via multiple testing sessions. PURPOSE: To determine the reliability of ADP measurements with and without pretest instructions both between days and on the same day. METHODS: Participants (n=19; 14 females, 5 males, age 20.8±1.4 years, weight 69.2±12.5 kg) completed four testing sessions across two days. ADP testing on day one occurred in the morning (T1) and afternoon (T2) and 48-hours later another morning (T3) and afternoon (T4) test were completed. For T1, participants were not provided with pretest instructions and were asked to maintain normal activities. Standard pretest instructions were provided for all subsequent visits. At each session, a standard ADP measurement was completed with participants wearing manufacturer-approved clothing and lab-issued swim cap. Data were analyzed using paired samples t-tests to determine the effect of pretest instructions and Pearson correlations to determine test-retest reliability with an alpha level set at 0.05. RESULTS: Pretest instructions did not change body volume (BV; T1 66.3±12.4 vs. T2 66.2±12.4 L; p=0.33) or body fat (BF; T1 23.4±6.9 vs. T2 23.6±7.1 %; p=0.54) across same day measures. However, differences were detected for BV (T1 66.3±12.4 vs. T3 65.7±12.2 L; p<0.01) and BF (T1 23.4±6.9 vs. T3 22.7±7.3%; p=0.04) for measures completed on different days. Test-retest reliability for BV and BF was high across different days (r≥0.97, p<0.01). CONCLUSIONS: Pretest instructions did not change ADP measures on the same day, suggesting they may not be necessary to attain measurements within standard error of estimate for ADP. However, differences were found between scores across different days, although these were also within ADP standard error. Between day test-retest reliability was high for BV measurements and BF estimations, with greater variability noted in BF. Future research would be important to ascertain how varying amounts of food and fluid consumption, as well as participation in exercise prior to testing can affect the reliability of ADP measures. Quantifying these factors may provide insight on threshold measures to follow.

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