The aim of the present study was to evaluate and compare the body composition and the cardiorespiratory performance as well as to examine the isokinetic muscle strength of the lower extremities and the vertical jump performance in professional, semi-professional and amateur Greek soccer players of the same club. Subjects formed three groups: professionals, U-21 and U-17. All subjects underwent anthropometric measurements, body fat assessment and performed a maximal exercise test on treadmill to determine VO^sub 2max^. Jumping ability was measured with two different tests and muscle strength of the quadriceps and hamstrings was examined at three angular velocities. The absolute values of VO^sub 2max^ (ml/min) were higher in professionals compared to U-21 and U-17 (p<0.05, p<0.001) while the relative values (ml/kg/min) did not differ between groups. Professionals presented significantly higher values in SJ and CMJ compared to U-21 by 11.3% and 10.5% and U-17 by 10.5% and 9.4%, respectively (p<0.001 and p<0.01). Professionals and U-21 demonstrated higher peak torque values at all angular velocities of knee flexors and extensors compared to U-17 (p<0.05, p<0.001). Conclusively, the professionals obtained higher values in muscle strength and jumping ability. These findings can be attributed to age, training experience, and specific strength training program. Moreover, the cardiorespiratory performance and body composition may be improved if the specific training program is followed by a balanced diet too.
Key words: physiological profile, VO2max, isokinetic muscle strength, vertical jump, physical fitness, elite soccer.
Soccer is a team sport with an intermittent nature of physical activity. It primarily involves running but also explosive-type efforts such as sprints, jumps, tackles, kicking, changing pace and duels for winning the possession of the ball (Cometti et al., 2001). All these actions require a variety of skills which must be combined so that to ensure that the player's performance will be successful. Such explosive actions often turn out to be decisive in game situations that lead in scoring. The ability to generate explosive muscle force within fractions of a second is an important determinant of performance (Thorlund et al., 2009). The execution of technical skills followed by effects of fatigue may cause an increase in playing errors (Mohr et al., 2003; Lyons et al., 2006; Huijgen et al., 2009). Muscle fatigue is difficult to define but is has been reported as the inability to maintain the required or expected force in the initial high level (De Ste Croix et al., 2003; Westerdlad et al., 1991). For these reasons, it is important for aerobic performance and muscle strength to be examined for high level amateurs and young soccer players.
There seems to be a high relevance between high levels of cardiorespiratory endurance and competitive ranking, quality of play and distance covered during a soccer match (Bangsbo and Linguist, 1992; Krustrup et al., 2003; Impellizzeri et al., 2005, Wisløffet al., 1998). Previous studies have shown that the values of VO2max professional soccer players vary from 55 - 65 ml/kg/min (Metaxas et al., 2009; Metaxas et al., 2005; Ekblom, 1994; Reilly et al., 2000) and 65-70.7 ml/kg/min in young players (Chamari et al., 2005). Muscle strength deficiency has been thought to be as one of several risk factors for hamstring injury (Yamamoto, 1993; Worrell, 1994; Askling et al., 2003). Knee flexor strength is extremely important in a soccer player because it provides joint stabilization during soccer-related actions and maneuvers (Aagaard et al., 1996; Cometti et al., 2001). Quadriceps peak torque values that have been reported in the bibliography (Metaxas et al., 2009) are 256 - 270 Nm at 60o.sec-1 in different division players and hamstring values are 144 - 155 Nm at the same angular velocity.
Jumping and pivoting is also frequently performed in soccer. …