# Optimizing Field Body Fat Percentage Assessment in Professional Soccer Players
## 4 Discussion
supraspinale, and abdominal SKF showed best correlation with DXA-derived %BF. Similar correlation was reported by [PERSON] et al. (2018), for the sum of these four SKF measurements. According to [PERSON] et al. (2009), a different set of four SKF measurements (anterior thigh, abdominal, triceps and calf), shows even better agreement with DXA. However, this new equation was found here to correlate less well with DXA as well as in the studies of [PERSON] et al. (2018) and [PERSON] et al. (2018). Hence, the sum of several SKF measurements could be a good option to estimate %BF in soccer players, as it was suggested by the UEFA's expert nutrition group [4]. We recommend the sum of triceps, subscapular, supraspinale, and abdominal SKFs, as the use of more did not offer any additional benefit and could weaken correlation with DXA as shown by our results and those of [PERSON] et al. (2018) and [PERSON] et al. (2018). BIA is a widely used method to assess body composition but it is of limited accuracy for estimating body fat [8]. Although BIA has been validated in clinical practice [44], few studies in athletes have compared BIA with a reference method such as DXA [9]. In our study, BIA was found to show the lowest correlation with DXA and also it significantly underestimated %BF in comparison with this reference method. Skinfold measurements were better predictors of DXA-derived fat mass than BIA in our study population, which is consistent with the findings of others in male elite soccer players [2; 5]. Consequently, BIA does not seem valid for assessing %BF in soccer players, as its measurements vary significantly from those provided by the reference method. Moreover, it correlated poorly with anthropometry equations or absolute SKF measurements. One of the main limitations of body composition assessment has been the use of numerous types of devices and brands [9]. Here, we used three methods to estimate %BF and the anthropometric procedure was performed following ISAK guidelines [20] by an accredited level I anthropometrist. In similar studies, the same three methods were used, and the same guidelines were followed for anthropometry. However, in each study different instruments and equations were used. Thus, it is difficult to compare the results of the studies that have examined this issue limiting the identification of the best anthropometry equation to analyze %BF in elite soccer players. The use of DXA as a reference method has been also considered a limitation [2], as it has shown moderate accuracy and precision for %BF in highly trained team sports players [44]. Another limitation of our study was the small sample size. As a strength, participants were a homogeneous group of elite soccer players from a professional Spanish club competing at the highest national level (i.e., La Liga) who had the same level of training and similar diet. However, the individual amount and type of training performed by players was not recorded. Additionally, this study used a cross-sectional design which does not allow to determine the most effective field methods for measuring changes in %BF with confidence [2]. Therefore, further longitudinal studies are needed to accurately measure %BF over time in elite soccer player. Additionally, further studies involving female soccer players and players of different levels of competition are needed. DXA is a widely accepted reference method for assessing fat mass in athletes. However, the equipment is costly, and it is not usually accessible to most sport clubs. Thus, field methods such as anthropometry and BIA are used to evaluate body composition in athletes. Of these methods, anthropometry seems a better option, and while it is a low-cost and practical method, it should be performed by an accredited anthropometrist and following ISAK guidelines. Moreover, the best anthropometry equation to estimate %BF needs to be selected as there are several options and they do not seem interchangeable with each other or with the reference method.