Investigations in the physiological demands of soccer have identified that a significant percentage of energy production in match performance is provided through the aerobic pathways. It is therefore important to assess maximal oxygen uptake (V[O.sub.2Max]) of players in order to evaluate their aerobic fitness status and optimize their physical conditioning. However, it is also important to consider the variation of (V[O.sub.2Max]) profiles for soccer players, with differences having been identified in terms of playing position as well as playing style. This paper reviews the academic literature between 1996 and 2006 and reports on the methodologies employed and the values obtained for stature, body mass and (V[O.sub.2Max]) profiles of soccer players of different positions in professional Brazilian clubs at U-17, U-20 and First Division levels. Indirect measurements accounted for the majority of tests conducted at U-17 (70%) and U-20 (84.6%) levels whereas at First Division level almost half of the (V[O.sub.2Max]) evaluations were performed by direct measurements (47.8%). The mean (V[O.sub.2Max]) profiles obtained for outfield players in U17 was 56.95 [+ or -] 3.60 ml x [kg.sup.-1] x [min.sup.-1], 58.13 [+ or -] 3.21 ml x [kg.sup.-1] x [min.sup.-1] for U-20 players and 56.58 [+ or -] 5.03 ml x [kg.sup.-1] x [min.sup.-1] for First Division players. In Brazil, the U-20 players appear to have highest V[O.sub.2Max] values, however the profiles reported for all outfield positions in U-17 and First Division levels are often lower than those reported for the same category of players from other countries. This may be a reflection of the style of play used in Brazilian soccer. This is further emphasized by the fact that the playing position with the highest V[O.sub.2Max] values was the external defenders whereas most findings from studies performed in European soccer indicate that midfielders require the highest V[O.sub.2Max] values.
Key words: Soccer, maximal oxygen uptake, playing positions.
The exercise pattern of soccer can be described as dynamic, random and intermittent (Bloomfield et al., 2007) to an extent which makes physical conditioning of players a complex process. This pattern involves a myriad of physiological processes which act in random sequences throughout match-play and this provides a huge challenge for coaches to condition players for the specific requirements of the game. However, it has been established that in order to advance in playing level, players must develop their aerobic capacity to tolerate the physiological load at higher levels of play (Helgerud et al., 2001; Stolen et al. 2005; Wisloff et al., 1998). The total mean distance covered by the top-level players during match-play has been reported to be between approximately 10,000m to 13,500m with distinct differences observed between each playing position (Bangsbo et al., 2006; Barros et al., 2007; Di Salvo et al., 2007). Other researchers using sophisticated time-motion analysis techniques have suggested a higher mean distance of 13,746m for players in Champions League matches (Di Salvo et al., 2007). This could be otherwise represented as an exercise protocol of running ~150m every minute for 90mins, having a 15min rest period after the first 45mins. In order to achieve this, even at moderate intensity, a high demand is placed on the player's aerobic energy system. Also, when considering the anaerobic requirement for match-play, the necessity of a well developed aerobic system is vital in order to recover quickly between repeated bouts of high intensity anaerobic activity (Stolen et al. 2005). It is well documented that higher levels of aerobic fitness provides a player with greater involvement potential during a match (in European studies), with significant relationships reported between V[O.sub.2Max] and the total distance covered as well as the frequency of sprints made in a match (Bangsbo et al., 1991; Helgerud et al., 2001; Wisloff et al., 1998), with time spent in high intensity activity as well as the number of involvements with the ball by the player (Helgerud et al., 2001) and ultimately, the final classification of the team in competitions (Wisloff et al., 1998). These improvements in performance have been associated with a greater ability to offset fatigue through an enhanced oxidization of lipids as well as sparing of glycogen and lower lactate production (Henriksson & Hickner, 1996).
To establish a profile of the aerobic capacity of soccer players, it is critical to consider many different independent factors which include chronological age, biological maturity, training age, morphology and anthropometry as well as preferred playing position. In order to establish normative data, profiles should be categorized against a range of levels of performance, as it appears that higher performance levels require higher physical and physiological demands (Rienzi et al., 2000). In addition, the measurement process for aerobic capacity must be considered as many different protocols have been suggested which ultimately fall into two categories, namely direct evaluation through online gas analysis techniques under laboratory conditions or indirect protocols using field testing methods or ergometers such as treadmills. Finally, it is of extreme importance to recognize the time of season that the testing has been performed, the mental and physical state of the players, the conditioning regimen the players have been through and the immediate period leading up to the testing. Due to a myriad of these variables, a wide range of V[O.sub.2Max] and estimated total energy expenditure (Kcal) have been reported in the literature.
The aerobic capacity (V[O.sub.2Max]) represents the metabolic parameter that quantifies the maximal oxygen uptake of an individual and is an important performance indicator in soccer. Mean heart rate values for university level players in the first and second half have been converted to a V[O.sub.2] of 51.1 and 46.2 ml x [kg.sup.-1] x [min.sup.-1] respectively (Bangsbo, 1994). However, it has been established that these values of V[O.sub.2] are unlikely to be a true reflection of aerobic energy requirements through the HR-V[O.sub.2] regression calculation and provide an overestimation of energy expenditure (Reilly, 1997). In general, for high level soccer players the reference values obtained from laboratories in peer-reviewed articles appear to range between 55-70 ml x [kg.sup.-1] x [min.sup.-1] (Bangsbo et al., 1991; Casajus, 2001; Kemi et al., 2003; Stolen et al., 2005), with some individual values reported as superior to 73 ml x [kg.sup.-1] x [min.sup.-1] (Silva et al., 1999). Also, direct V[O.sub.2] measurements from match-play have been measured although the method is limited due to the inhibition of full involvement in soccer performance due to the restrictions from the equipment needed (Kawakami et al., 1992; Reilly, 1997). Therefore, it is suggested that players should have V[O.sub.2Max] values superior to 60 ml x [kg.sup.-1] x [min.sup.-1] in order to be competitive at the highest levels in soccer (Reilly et al., 2000), although it is important to note that this is not a limiting factor to successful performance. Determining V[O.sub.2Max] of soccer players is therefore useful when assessing talent, in selection of players, in the design of physical conditioning programmes, predicting and monitoring physical match performance. Therefore, establishing reference parameters in high performance can assist in making important informed decisions, particularly for the strength & conditioning staff at soccer clubs and National teams to manipulate physical training to optimize the regimes.
Several recent studies have reported data of V[O.sub.2Max] values from First Division soccer players of high level teams from the European soccer league (Casajus, 2001; Dupont et al., 2005; Edwards et al., 2003; Kemi et al., 2003; Wisloff et al., 1998). From these data, it appears that players have increased aerobic capacity in these European studies in recent years. There may be several reasons for this increase which may include a higher number of sport science and conditioning practitioners appointed in top-level European clubs performing sophisticated profiling, prescription and monitoring of training as well as the increased use of technologies to analyze and performance (Carling et al., 2008). However, the development of aerobic capacity of soccer players playing in Brazil has not been collated and reported which is surprising when considering the success of Brazilian National Teams in recent years in international competitions, including winning the FIFA World Cup in 1994 and 2002, the Copa America in 1997, 1999, 2004 and 2007 and the Confederations Cup in 2005. Thus, this present study aims to report on the stature, body mass and V[O.sub.2Max] profiles of Brazilian soccer players reported since 1996, draw some comparisons with other playing nations and provide contemporary data for players identified by age category and playing position, in particular to provide reference for coaches and practitioners in Brazil and in Europe, where many Brazilian players are signed to European clubs.
In order to track the physical and physiological development of Brazilian soccer players, a review of International and Brazilian sport science journal publications between 1996 and 2006 was undertaken. Inclusion categories for this study included each publication had to have been subjected to peer-review and contain the provision of data concerning the biographic, anthropometric and maximal oxygen uptake (V[O.sub.2Max]) values from high level male Brazilian soccer players in any of the First Division, U-17 (under 17 years old), U-20 (under 20 years old) categories and First Division State and National clubs. Internet sources where utilized to access electronic journal databases including Medline...