Journal of Physical Education and Sport

Abstract

IntroductionSoccer 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, Wisloffet 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. As a player jumps an average of 15.5 times during a soccer game (Reilly and Thomas, 1976) and for every 2 turns a player performs during a game, a landing from a jump or header occurs (Withers et al., 1986). Studies have shown that landing with decreased knee flexion may increase the forces on the anterior cruciate ligament (ACL) (Griffin et al., 2000). According to Boden et al. (2000) most ACL injuries occur when the knee is near full extension during a sharp deceleration or while landing after a jump. This extended position of the knee joint, together with eccentric contraction of the quadriceps muscle, increases the strain on the ACL and it may lead to an injury, especially if there are low levels in muscle strength or muscle imbalances between the hamstrings and quadriceps. Soccer players should be taught correctly the technique in landing after a jump which demands a smaller knee flexion angle, as the extended knee may have less dynamic control and the ability to absorb the produced forces (Lloyd et al., 2005). Cometti et al. (2001) examined vertical jump in three different divisions and demonstrated CMJ values of 41.56 ± 4.18cm, 39.71±5.17cm, 43.93±5.65cm in first, second and third division, respectively as well as SJ values of 38.48±3.8cm, 33.86±7.47cm, 39.83 ± 5.51 in each division, respectively. Recently, Wisloffet al. (2004) presented CMJ values of 56.4 ±4.0 cm in elite male soccer players which are similar to those observed by McMillan et al. (2005) in CMJ (53.4±4.2 cm) and in SJ 40.3±4.0 cm.Fat seems to be a very good insulator of the human body because it tends to preserve the heat that's been produced during exercise in the core of the body. …