Body composition assessment via bioelectrical impedance analysis: Standardized vs. unstandardized pre-assessment protocol

Objective This study assessed the repeatability and agreement of body mass (BM), fat mass (FM), fat-free mass (FFM), and total body water (TBW) using Bioelectrical Impedance Analysis (BIA) under standardized (SP) versus unstandardized procedures (UP). Materials and methods Twenty-seven volunteers (23.8 ± 2.4 years) underwent two BIA evaluations (InBody 120) on consecutive days: first under UP (UP1 and UP2), then under SP (SP1 and SP2). Coefficient of variation (CV%), standard error of measurement (SEM), and intraclass correlation coefficient (ICC; 95% CI) assessed repeatability. Multiple comparisons (UP1 vs. UP2 vs. SP1 vs. SP2) and effect size (ES) analyses were conducted. Agreement (SP vs. UP) was evaluated using mean difference (MD), ES, CV%, SEM, ICC, Lin's concordance correlation coefficient (CCC), and 95% limits of agreement (LoA). Results All comparisons showed high ICC values (0.98–1.00), no significant differences ( P > 0.29), very low CV% (0.06–1.34), and SEM (0.05–0.22). SP vs. UP comparisons revealed low CV% (0.45–4.53) and SEM (0.32–0.77). Small ES were observed (0.001–0.19), except in men for FFM and TBW (ES = 0.27–0.28). The smallest LoA (%) occurred for BM (women = 2.01, −2.09; men = 2.96, −2.59) and the largest for FM (women = 9.21, −12.11; men = 17.99, −20.35). LoA (%) for TBW and FFM were similar between sexes (ULoA% = 5.21–5.88; LLoA% = −4.80 to −5.36). Conclusion Consecutive BIA tests demonstrated strong short-term repeatability. Deviations from standardized pre-assessment primarily affected FM estimates, reinforcing the importance of standardization.