Age-Related Differences in Linear Sprint and Power Characteristics in Youth Elite Soccer Players

IntroductionMany contributing factors are relevant in determining the success of a soccer performance, especially that at the top level. Each player has different physical abilities, technical skills, tactical thinking and psychological characteristics and therefore he has his own role in the team. In terms of physical activity, there are different requirements on physical, physiological and bioenergetic expenditure. The soccer match is characterized by intermittent physical load in which periods of high intensity are alternated with periods of low intensity. Speed and explosive power are considered to be prerequisites for the success of youth soccer players (Reilly, Bangsbo, & Franks, 2000). High load intensity is a crucial element distinguishing players of elite and lower levels. Elite level players perform 2 - 3 km in higher running intensity (> 15 km/h) and 0.6 km in sprint (> 20 km/h) (Iaia, Rampinini, & Bangsbo, 2009). Elite players perform approximately 30 - 40 sprints of various lengths during a match and more than 700 turns (Bloomfield, Polman, & O'Donoghue, 2007). Stolen, Chamari, Castagna, and Wisloff (2005) reported that high-intensity activities occur approximately every 90 seconds during a match and last for 2 - 4 seconds. High intensity activity during the game is an important element in soccer because increasing speed over a short distance may be necessary not only for adults but also for youth soccer players in crucial phases of the game. For professional players, Andrzejewski, Chmura, Pluta, Strzelczyk, and Kasprzak (2013) reported that 90% of sprints were performed within 5 seconds. Some authors consider the player's first steps and the ability to gradually increase their speed as the most important component of the running performance during the game (Dellal et al., 2011; Sleivert & Taingahue, 2004). In terms of these findings, the 5 and 10 m tests appear to be suitable for the assessment of acceleration (Maly, Zahalka, Mala, & Teplan, 2014; Stolen et al., 2005; Strudwick, Reilly, & Doran, 2002; Teplan, Maly, Zahalka, & Mala, 2013). Faude, Koch, and Meyer (2012) stated that straight sprints are the most dominant actions when scoring goals in professional soccer. Most sprints were conducted without the ball. Thus, straight sprinting should be considered in fitness testing and training. However, players rarely reach their maximum speed during a match; therefore, the acceleration phase is crucial in game performance (Jovanovic, Sporis, Omrcen, & Fiorentini, 2011). Examining strength and power might be useful in monitoring professional soccer players' performance. Vertical jumping performance is a simple indicator of muscular strength of lower extremities and it is often used in assessment of changes caused by specific training (Kotzamanidis, Chatzopoulos, Michailidis, Papaiakovou, & Patikas, 2005; Siegler, Gaskill, & Ruby, 2003; Zahalka, Maly, Mala, Teplan, & Hrasky, 2013). When assessing jumping performance, the most commonly measured parameters include the jump height achieved, maximum force produced at the take-off, rate of force development and also a shape of force-time curve during the jump is described. Gauffin, Ekstrand, Arnesson, and Tropp (1989) reported in their study that players from first two teams in the French highest league achieved better results in vertical jumps compared with teams at lower positions in the league table while Wisloff, Helgerud, and Hoff (1998) in a similar study in Norwegian elite soccer league found no significant differences between the first and last classified team. A vertical jump is one of decisive factors in soccer players. It is a complex action that depends on coordination (Bobbert & Schenau, 1988; Zahalka, Maly, Mala, & Teplan, 2012), type of muscle fibre and its stiffness (Bobbert, 2001) and maximum strength (Baker, 1996). Wisloff, Castagna, Helgerud, Jones, and Hoff (2004) reported that there is significant correlation between the vertical jump height and speed abilities in 30 m sprint; however, Chamari et al. …