Reliability of Air Displacement Plethysmography in a Large Sample

0482 Several studies have examined the validity of air displacement plethysmography (ADP) as a means of measuring body volume (BV) and assessing body density (Db) in humans. However, few studies have been done to assess the reliability of ADP. PURPOSE: To determine the reliability of ADP using the BodPod® in a large sample. METHODS: 980 healthy men and women (30 ± 15y, mean ± SD) completed two body composition assessments separated by 15–30 min. Some of these subjects (n = 348) completed a total of three body composition assessments. All testing was done in accordance with the manufacturer's instructions. RESULTS: Results from 2 tests: There was a significant correlation (r = 0.992, p = 0.001) between Db 1 (1.0463 ± 0.0009 kg/l [mean ± SEM]) and Db 2 (1.0463 ± 0.0009 kg/l). A paired t-test revealed no significant difference between Db 1and 2 (p = 0.935). The coefficient of variation (CV) for Db was 0.15%. Body Mass (BM) 1 and 2 were correlated significantly (r = 0.999, p = 0.001); however, there was a significant (p = 0.001) decrease from BM 1 (75.5095 ± 0.4612 kg) to BM 2 (75.4974 ± 0.4611 kg). BV tended to decrease (p = 0.08) from BV 1 (69.8998 ± 0.4491 l) to BV 2 (69.8840 ± 0.4486 l). Results from 3 tests: There were no significant differences found for Db among the 3 trials (1.0455 ± 0.0015 kg/l, 1.0454 ± 0.0015 kg/l, 1.0457 ± 0.0015 kg/l). The CV for Db was 0.18%. There was a significant decrease with time from BM 1(74.7607 ± 0.7646 kg) to BM 2 (74.7518 ± 0.7645 kg; p = 0.007) and from BM 2 to BM 3 (74.7460 ± 0.7645 kg; p = 0.001). BV decreased (p = 0.043) from BV 1 (69.2607 ± 0.7466 l) to BV 3 (69.2286 ± 0.7450 l). CONCLUSION: ADP using the Bod Pod® appears to assess Db reliably; however, the observed CV suggests that multiple trials are necessary to detect small treatment effects. Performing 3 trials instead of 2 does not appear to increase the reliability. The slight, but significant, reduction in BM seen over a short period of time suggests that the scale is sensitive enough to detect metabolic/evaporative mass loss. Supported by The Joe Weider Foundation