Seasonal body composition alterations of an elite male soccer team evaluated with skinfold thickness equations and BIMP analysis

The purpose of this study was classified in two aspects: (1) evaluating seasonal changes in body composition of an elite male soccer team; (2) comparing body fat estimates of two different skinfold thickness equations ( Jackson-Pollock (JP), Withers) to those of multifrequency bioimpedance (BIMP) among soccer players. Skinfold thickness (7-site) and BIMP measurements were done to 24 players from the same team at 5 different time points throughout the season of 2016-2017. Team displayed no seasonal changes in any of the body composition parameters (body weight, muscle mass, body fat, bone mass, body water, visceral fat rate) (P>0.05). According to Bland-Altman plot analysis for repeated measures, bias between BIMP and JP estimates was 2.88 +/- 2.94, whereas bias between BIMP and Withers estimates was 0.53 +/- 2.13 and limits of agreement ranged between -2.83 and 9.69 for JP and BIMP, and between -3.57 to 4.76 for Withers and BIMP. A poor correlation was observed between JP and BIMP (rho(c)=0.29, 95% confidence interval (CI) [0.18-0.39]). Assessment between BIMP analysis and Withers formula returned a fair correlation (rho(c)=0.49, 95% CI [0.34-0.61]). Finally, Withers and JP formulas' estimates displayed only a moderate correlation (rho(c)=0.66, 95% CI [0.60-0.72]). Either of the methods cannot be used interchangeably, therefore longitudinal tracking of body fat must be done with a single method and equation. When 7- site skinfold measurements are conducted, we suggest implementing Withers equation among elite male soccer players.