## 4 Discussion
### Body Composition Values  
In soccer, there are different playing positions with their own demands and characteristics [2; 3; 9; 10; 49]; several working groups have tested whether or not there are significant differences in body composition [16; 44; 50]. While most studies apply a horizontal subdivision for playing positions (goalkeeper, defender, midfielder, and forward), it would be advisable to also make a vertical subdivision (central defender, lateral defender, attacking midfielder, central midfielder, defensive midfielder, and winger) to further specify the anthropometric characteristics, activity profiles, and/or physiological demands of each player [49]. Previously some studies investigated the differences in body composition between different playing positions. In a study of 64 professional players from four different English Premier League teams, body composition was analyzed by DXA, dividing the subjects by playing positions (goalkeeper, defender, midfielder, and forward). Goalkeepers differed from the other positions in both anthropometric and body composition variables, being the tallest (1.90 \(\pm\) 0.03 m), heaviest (91.2 \(\pm\) 4.60 kg), and with the highest percentage of FM (12.9 \(\pm\) 2.00%) [44]. Most recently, [PERSON] et al. also analyzed the differences between the different playing positions (goalkeeper, defense, midfielder, and forward) in 57 soccer players of the same Spanish league club through anthropometry and BIA. The highest fat percentages were obtained in goalkeepers (9.40 \(\pm\) 1.40%), followed by defenders (8.00 \(\pm\) 1.60%) with respect to the rest of the positions (midfielders 7.40 \(\pm\) 1.30% and forwards 7.70 \(\pm\) 1.40%) [16]. Ziv & Lidor published a review where they evaluated the physical characteristics and physiological attributes of goalkeepers, highlighting that they are generally taller than 180 cm, with a body weight over 77.0 kg and a percentage of FM around 12.0-14.0% [50]. Lastly, the Union of European Football Associations (UEFA) expert group statement [12] also reported that the goalkeeper was the playing position with the highest values for height, weight, and FM. In our work, in relation to goalkeeper height and weight, with the exception of one study [27], all show these characteristics [23; 25; 26; 28; 29; 30; 31; 32; 33; 44; 46; 47; 48; 51; 52]. Although the percentages of FM coincide in several studies [27; 31; 42; 44; 48; 51], there are exceptions above [23; 26; 46; 47; 52] and below the range suggested by [PERSON] & Lidor [32; 37; 43; 51]. Although the goalkeeper is often attributed as the position with the highest FM, as shown in Table 3, there were no statistically significant differences for both the percentage and weight of FM compared to the other playing positions. However, the sum of six skinfolds, which is correlated with FM, did show statistical differences, with the goalkeeper havingthe highest sum of skinkolds (58.8 mm). These results could be justified due to the fact that the goalkeeper, during training and especially in matches, in general, travels shorter distances than the rest of the playing positions, so it is reasonable that the goalkeeper is the playing position with the highest sum of skinkolds. In addition, due to their sporting role, they need to have a vertical jump and a developed wingspan in order to block the shots of the opposing team, which would justify the results obtained in relation to height, weight, and muscle mass [9; 10; 12; 50]. In the case of the defenders, they appear to be in the position with the highest total weight and MM together with the goalkeepers. This makes sense because, due to their role in the game, it is a very physical position in which they must stop attackers by intercepting plays both on the ground and in the air and initiate offensive plays on many occasions. Midfielders are the shortest and lightest, as well as showing similar values to forwards in MM and FM.