Concordance between Laboratory and Field Methods for the Assessment of Body Fat in Olympic Combat Athletes: Analysis of the Influence of Adiposity

Abstract

Combat sports athletes competing in the same discipline exhibit notable and substantial differences in body weight, body composition (BC) and adiposity. No studies have considered the influence of adiposity levels in the agreement between different BC assessment methods. The aim of this study was to analyze the influence of adiposity in the agreement between different methods used to estimate relative body fat (%BF) in Olympic combat sport athletes. A total of 38 male athletes were evaluated using air displacement plethysmography and dual-energy X-ray absorptiometry (DXA) as laboratory methods, and bioelectrical impedance analysis (BIA), near-infrared interactance (NIR) and anthropometry as field methods. All methods were compared to DXA. Agreement analyses were performed by means of individual intraclass correlation coefficients (ICCs) for each method compared to DXA, Bland−Altman plots and paired Student t-tests. The ICCs for the different methods compared to DXA were analyzed, considering tertiles of %BF, tertiles of body weight and type of sport. For the whole group, individual ICCs oscillated between 0.806 for BIA and 0.942 for anthropometry. BIA showed a statistically significant underestimation of %BF when compared to DXA. The agreement between every method and DXA was not affected by %BF, but it was highest in athletes at the highest %BF tertile (>13%). The ICC between NIR and DXA was poor in 72−82 kg athletes. Our results indicate that field methods are useful for routine %BF analysis, and that anthropometry is particularly appropriate, as it showed the highest accuracy irrespective of the athletes’ adiposity.

Keywords: Olympic combat sports; adiposity; body composition; elite athletes; methods agreement.

Figure 1

Bland–Altman plots representing the difference between DXA-derived %BF and %BF determined using (a) anthropometry, (b) BOD POD, (c) NIR and (d) BIA. The central dotted line represents the mean inter-methods difference. The upper and lower broken lines represent the 95% limits of agreement (inter-methods difference ± 1.96 SD of the differences). Abbreviations: %BF = percentage of body fat; DXA = dual-energy X-ray absorptiometry; BOD POD = air displacement plethysmography; NIR = near-infrared interactance; BIA = bioelectrical impedance analysis; SD = standard deviation.

Figure 2

Forest plot: ICC (crude) and 95% confidence interval for the relationship between BMI and %BF (measured by BOD POD, BIA, NIR, and anthropometry) by subgroups (sport) or tertiles (%BF measured by DXA and weight). Abbreviations: ICC = intra-class correlation; CI = confidence interval; BMI = body mass index; %BF = percentage of body fat; BOD POD = air displacement plethysmography; NIR = near-infrared interactance; BIA = bioelectrical impedance analysis; DXA = dual-energy X-ray absorptiometry.