Kilduff, L.P., S. Lewis, M.I.C. Kingsley, N.J. Owen, and R.E. Dietzig. Reliability and detecting change following short-term creatine supplementation: Comparison of two-component body composition methods. J. Strength Cond. Res. 21(2): 378–384. 2007.—The purpose of the present study was twofold: firstly, to assess the reliability of various body composition methods, and secondly, to determine the ability of the methods to estimate changes in fat-free mass (FFM) following creatine (Cr) supplementation. Fifty-five healthy male athletes (weight 78.3 10.3 kg, age 21 1 years) gave informed consent to participate in this study. Subjects’ FFM was estimated by hydrostatic weighing (HW), air-displacement plethysmography (ADP), bioelectrical impedance analysis (BIA), near-infrared spectroscopy (NIR), and anthropometric measurements (ANTHRO). Measurements were taken on 2 occasions separated by 7 days to assess the reliability of the methods. Following this, 30 subjects returned to the laboratory for an additional test day following 7 days of Cr supplementation (20 g·d1 Cr 140 g·d1 dextrose) to assess each method’s ability to detect acute changes in FFM. In terms of reliability, we found excellent test-retest correlations for all 5 methods, ranging from 0.983 to 0.998 (p 0.001). The mean biases for the 5 methods were close to 0 (range 0.1 to 0.3 kg) and their 95% limits of agreement (LOAs) were within acceptable limits (HW 1.1 to 1.7 kg; ADP 1.1 to 1.2 kg; BIA 1.0 to 1.0 kg; NIR 1.4 to 1.4 kg); however, the 95% LOAs were slightly wider for ANTHRO (2.4 to 2.6 kg). Following Cr supplementation there was a significant increase in body mass (from 77.9 10.1 kg to 78.9 10.3 kg, p 0.000). In addition, all 5 body composition techniques detected the change in FFM to a similar degree (mean change: HW 0.9 0.6 kg; ADP 0.9 0.6 kg; BIA 0.9 0.6 kg; NIR 0.8 0.5 kg; ANTHRO 1.0 0.7 kg; intraclass correlation coefficient 0.962). We conclude that between-day differences in FFM estimation were within acceptable limits, with the possible exception of ANTHRO. In addition, all 5 methods provided similar measures of FFM change during acute Cr supplementation.

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