Soccer is considered the most popular sport in the world, being practiced in almost all nations (Reilly & Williams, 2003), and as sporting performance evolves, concerns about the factors involved in its improvement increases, so that the monitoring of body composition variables to achieve better results becomes more important. Accordingly, given morphological characteristics obtained in the anthropometric assessments and in the body composition (body mass [BM], height, fat free mass [FFM] and fat mass [FM]) are important to excel in soccer.

Due to the size of the soccer pitch and the duration of the game, each players performs one specific function within the team, showing specific physical characteristics (Davis, Brewer, & Atkin, 1992; Goulding et al., 2009; Silvestre, West, Maresh, & Kraemer, 2006; Sporis, Jukic, Ostojic, & Milanovic, 2009)

Aside from some research which has been carried out with these athletes (Carling & Orhant, 2010; Casajus, 2001; Davis et al., 1992; Franks, Williams, Reilly, & Nevill, 1999; Reilly, Bangsbo, & Franks, 2000; Rhodes et al., 1986; Rienzi, Mazza, Carter, & Reilly, 1998; Silvestre et al., 2006), sports science has been more dedicated to the studies of aerobic and anaerobic fitness, with less attention given to the morphological variables, which are generally studied by a bi-compartmental model of evaluation (BM= FFM+ FM).

Research having as main framework multi-compartmental models in which the body is split into three or more components is a must (Heyms­field, Wang, Visser, Gallagher, & Pierson, 1996), allowing a detailed study that takes into consideration the distribution of the FFM in a segmented way. Additionally, there are few studies that have investigated the body composition of Brazilian soccer players, and analyzed according to field position. Thus, the objective of the present study was to analyze the body composition and bone mineral density of athletes from elite Brazilian soccer teams and to compare the differences between the field positions.

These athletes competed in a league with 20 teams and the season lasted for 11 months of the year. Because there are only a few breaks over the season, data collection was done during the pre-season.

From an ethical point of view, the related project was approved by the Ethics Research Group of the university (Protocol nº 48/2010). All participants were fully informed about the nature and demands of the study, as well as the known health risks. They completed a health history questionnaire and were informed that they could withdraw from the study at any time. All participants signed a written consent form.

Instruments and Procedures

Anthropometry and Body Composition

Body mass was measured with an electronic weighting scale (Filizola®), with a maximum capacity of 180 kg and a precision of 0.1 kg. Height was measured with a fixed stadiometer (Sanny ®), with an accuracy of 0.1 cm and
a length of 2.20 m.

To estimate fat free mass, fat mass, percentage of body fat, fat free mass of legs and bone mineral density, an absorptiometry device for X-ray of Dual-energy (DEXA) of Lunar brand was used, DPX-MD, software 4.7 The DEXA body composition was estimated by dividing the body into three anatomical compartments: fat-free mass, fat mass and bone mineral density (BMD). Results are reported in grams of lean mass, fat and body fat percentage (Lohman, Roche, & Heymsfield, 1996). This technique also allows the estimation of total and segmental body composition. Thus we estimated the total body composition and lower limb.

The determination of the body regions was done according to Silvestre et al. (2006). All evaluations were performed in competitive pre-season.

Table 2 presents the different body compositions according to player position. The positions LM (10.5 ± 5.2), CM (9.7 ± 4.0) and FW (9.9 ± 4.4) had lower values of FM and %FM than both the GK (17.3 ± 6.0) and the control group (15.0 ± 5.3). Compared to the other positions, FFM was higher in the GK (68.2 ± 10.9) and BF (64.6 ± 6.8) (p< 0.05). No significant differences were verified in FFM-Legs among the athletes groups but all of them presented significantly higher values than the CG (p< 0.05).

In this study the soccer players, when compared to the control group, showed differences in all variables, but for age and weight, showing the effect of specific training in this sport. The average percentage of fat found in soccer players was 14%, values similar to those found by Silvestre et al. (2006) (13.9%) and Matkovic et al. (2003) (14.9%) with first division players from Connecticut and Croatia respectively. However, they are all higher than those shown by Sutton, Scott, Wallace, and Reilly (2009) who evaluated four of the elite English soccer teams. These differences may be due to the instruments used and evaluation period (pre-season or period of competitions), as well as the competitive level of the participants. Gissis et al. (2006) analyzed the values of body fat in soccer players according to their competitive level in the Greek league teams, showing significantly lower values in the best placed teams.

Sutton et al. (2009) showed that body fat and bone mineral density are the best variables to discriminate soccer players from the control group, according to multiple regression models, this effect was observed in the goalkeepers. In the study by Sutton et al. (2009) goalkeepers showed higher values of body fat percentage when compared to other field positions. These results are similar to those found in this study; however, goalkeepers only differed from midfielders and attackers.

These differences in fat percentage between goalkeepers and defenders from the remaining positions may be due to the characteristics required in training and games. Reilly (1997) noted that goalkeepers and defenders run on average 4 and 8 km, respectively, in a match, while in other positions the distance can reach 12 km. So it is natural that goalkeepers would have a lower aerobic capacity and a higher percentage of body fat.

Matkovic et al. (2003) and Arnason et al. (2004) reported greater differences between goalkeepers and other player positions, with goalkeepers being taller, heavier and having a higher fat percentage. In these two studies small differences between the other positions (goalies excluded) were also found.

In this research, goalkeepers also had a higher absolute amount of fat-free mass compared to the control group, the laterals, midfielders and attackers. However, when only the fat-free mass of the legs was analyzed the difference found was only in relation to the control group. Sutton et al. (2009) used the percentage of fat-free mass and found no differences between the positions of play. These two pieces of information show the importance of different forms of analysis.

Soccer players have differences in all body composition variables. In this study goalkeepers and defenders were taller and heavier than the players from the sidelines, the midfield and the attack. However, the values of fat-free mass are influenced by different types of methods which can be used for estimation of the body composition and how the values are used (absolute and relative).

There were no differences in BMD between soccer players, according to field position, but when the soccer players were compared with the control group there were differences (p= 0.001). Fredericson et al (2007), compared the BMD of soccer players with runners and sedentary men, and noted that soccer players' total BMD only showed a difference with the control group, which is similar to our findings. The highest BMD values found among players can be explained, because soccer is a sport that involves activities and intermittent high intensities, which include sprinting, jumping, accelerations, decelerations and quick changes of direction, which involve the stimulation of acquiring bone mineral (Heinonen, Sievanen, Kyrolainen, Perttunen, & Kannus, 2001; Robling, Hinant, Burr, & Turner, 2002).

The data from the present study provides an insight of the anthropometric characteristics and the body composition of professional soccer players. That said, some limitations should be addressed. The goalkeeper being a position with a smaller number of athletes on the team, the data collection season and not having a diet control group.

The results of this study show that soccer players have specific morphological characteristics related to body composition as compared to a control group. However, only goalkeepers differed as compared to the other player positions.

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Acknowledgments:
Nothing to declare.
Conflicts of Interest:
Nothing to declare.
Funding:
Nothing to declare.

Manuscript received February 27, 2014; Revised April 21, 2014; Accepted April 25, 2014

*Corresponding author: Departamento de Educação Física, Universidade Estadual Paulista (UNESP), Rua Roberto Simonsen, nº 305 – Centro Educacional, Presidente Prudente, CEP 19060-900 São Paulo, Brasil; E-mail: netoef@yahoo.com.br