Intra- and inter-session reliability of air plethysmography for assessing body composition in university athletes

Pretesting guidelines for assessing body composition using air plethysmography pose significant difficulty when assessing hundreds of university athletes. Furthermore, there is limited evidence concerning the typical error for indices of body composition in Canadian female and male university athletes. This was a test–retest study examining the intra- and inter-session reliability of the BOD POD® system (COSMED, Rome, Italy) for assessing body composition. A total of 44 university athletes volunteered as participants (♂n = 22 and ♀n = 22). Athletes were assigned two measurements on day 1, a morning (AM₁) and an afternoon (PM) measurement. On day 2, participants returned for their second morning measurement (AM₂). Each morning measurement required participants to be fasted and not have performed exercise for a minimum of 2 h, while the afternoon measurement disregarded all pretesting guidelines. The typical error (TE) from the intra-session reliability (AM₁ vs. PM) in males and females was minimal for body weight (TE ≤ 0.50 kg, p ≤ 0.006), body fat (TE ≤ 0.87%, p ≥ 0.244), and fat-free mass (TE ≤ 0.67 kg, p ≤ 0.067). The TE from the inter-session reliability (AM₁ vs. AM₂) in males and females was marginal for body weight (TE ≤ 0.45 kg, p ≥ 0.949), body fat (TE ≤ 1.10%, p ≥ 0.195), and fat-free mass (TE ≤ 0.83 kg, p ≥ 0.462). This study demonstrated excellent reliability for assessing body composition when negating pretesting guidelines and offers practitioners multiple possibilities for establishing the smallest meaningful change in body composition.