The Influence Of Posture On Bioelectrical Impedance Analysis In Adults

PURPOSE: To examine whether pre-testing posture influences percent body fat measurements determined by bioelectrical impedance analysis. METHODS: One-hundred thirty-one adults (67 females; 64 males) volunteered to participate in this study (age = 21.6 ± 3.5 years; body mass index = 25.4 ± 4.7 kg/m2). Body mass and percent body fat (%BF) were measured using leg-to-leg bioelectrical impedance analysis (LBIA; Tanita 300-A), segmental bioelectrical impedance analysis (SBIA; Tanita BC-418) and multifrequency bioelectrical impedance analysis (MFBIA; InBody 770) during two separate conditions (seated and standing) within a 7-day period. After an initial baseline measurement of body mass and %BF on each device, subjects were instructed to sit or stand for 15 minutes. Additional body composition measurements were recorded, in the standing position, at the 5 and 15-minute timepoints of each experimental trial. Body mass and %BF data from the three devices was assessed using two-way repeated measures ANOVA with Bonferroni-adjusted post-hoc tests. Alpha level was set a priori to p < 0.05. RESULTS: Body mass was not influenced by posture for either condition (seated or standing) or across any BIA device. Standing significantly (p < 0.05) reduced SBIA %BF at the 5-minute (23.4 ± 9.1%) and 15-minute (23.2 ± 9.0%) timepoints when compared to baseline (23.7 ± 9.1%). LBIA measured %BF was also significantly reduced after 5-minutes of standing when compared to baseline (24.3 ± 8.6% vs. 24.6 ± 8.6%; p < 0.05). No differences were observed in MFBIA assessed %BF during the standing condition. In addition, no differences were observed during the seated condition for any of the bioelectric impedance analyzers over time. CONCLUSIONS: Our findings demonstrate that prolonged standing (up to 15 minutes) prior to body composition assessment reduces %BF values when using LBIA and SBIA technology. However, the magnitude of change was relatively small (≤ 0.5%BF) and therefore expected to have little practical significance when making health recommendations.