# Optimizing Field Body Fat Percentage Assessment in Professional Soccer Players
###### Abstract  
Body composition is a determinant of performance in soccer. To estimate the body fat percentage (%BF), dual energy X-ray absorptiometry (DXA) is effective though this method is expensive and not readily accessible. This study examines the validity of widely used field methods based on anthropometric data and bioelectrical impedance analysis (BIA). Participants were 21 male Spanish First Division soccer players aged between 22 and 35 years. In each participant, body fat mass was determined by BIA and using 18 anthropometric equations including skinfold (SKF) measurements. DXA was used as reference. Correlation with DXA measurements was excellent for all equations and separate SKF measurements yet only moderate for BIA. However, only the equation recently developed for use in soccer players based on iliac crest and triceps SKFs showed no significant or standardized differences with DXA-derived %BF and these measurements also had the lowest bias. Our findings suggest that when DXA is not available, the best field method for %BF assessment in footballers is the equation based on iliac crest and triceps SKF. As another good option, we propose the sum of triceps, subscapular, supraspinal, and abdominal SKFs, as this combination also showed good correlation with DXA. football; fat mass; bioelectrical impedance; dual X-ray absorptiometry; skinfolds +
Footnote †: journal: Applied  
0000-0001-8898-2000]E. R.  
emits radiation, which although only scarce, will limit the frequency of measurements in soccer players, as in this sport, body composition needs be assessed at different time points during the season [4]. In professional players, body fat mass is commonly estimated through field methods such as bioelectrical impedance analysis (BIA) and anthropometric measures, especially skinfeld (SKF) thickness measurements [5]. Anthropometry is a cost-effective, acceptable, and practical method to assess body composition when conducted by a trained anthropometrist following appropriate guidelines, such as the recommendations of the International Society for the Advancement of Kiananthropometry (ISAK). Several equations for predicting fat mass have been developed for both non-athletic and athletic populations [6] although there are large differences between them. Moreover, only three equations have been specifically designed for football players, and these have not been validated for use in other sports modalities [2; 5; 7]. Hence, rather than estimating %BF using equations, the nutrition expert group of the Union of European Football Associations (UEFA) recommends the use of absolute SKFs to measure changes in body composition [4]. Therefore, the sum of SKFs measurement could be another valid alternative as an indicator of adiposity in professional soccer players, being a direct method without the need to apply any of the many existing equations, and showing a large relationship with DXA-determined body fat [2]. However, specific equations for elite male soccer players, explaining >78% variance in DXA-derived %BF using only two site skinfolds have been developed, measurement that can be performed in only 2-3 min [5]. We need reference values for fat percentage values with harmonization of anthropometric methodology in homogeneous elite male soccer players to get representative samples of professional soccer players. BIA has been widely used to estimate body composition. In football, this method is starting to gain popularity because of benefits such as its short measurement time, technical simplicity, and low cost [2; 8; 9; 10; 11]. However, its accuracy in determining %BF is limited [8] and its validity has not been proven against a reference method [9]. Additionally, for a proper evaluation, exercise should be avoided, which is an important limitation in athletes [8]. Many studies have used anthropometric equations to predict fat mass in professional soccer players [13; 14; 15; 16].