The Effects of an 8 Weeks Plyometric Training Program or an Explosive Strength Training Program on the Jump-and-Reach Height of Male Amateur Soccer Players

IntroductionVertical jumping is important in a variety of sports. In many sport situations, jumping ability may determine the success of failure of a competition. Superior, jumping ability is a skill that athletes may develop, in part, through specific power, speed, and strength training. Strength coaches use a variety of training methods (e.g., isotonic, isokinetic, and isometric training) to increase vertical jumping ability. Recently, plyometric training has been suggested to provide the speed and explosiveness needed to best improve vertical jumping ability (Von Duvillard et ak, 1990). The capacity of soccer players to produce varied forceful and explosive actions such as jumping highly influences soccer match performance (Reilly et ak, 2000). The capacity to repeat explosive bouts is an important determinant of player performance (Stroyer et ak, 2004). Training for maximal strength lias been suggested to play a major role in improving explosive actions as a result of an increased force availability (Cronin et ak, 2000). Plyometrics, with its Greek derivative, comes from "plythein", which means to increase and "metric", which means to measure (Wilk et ak, 1993). A plyometric maneuver is involved of developing eccentric muscle tension (lengthening) prior to the concentric contraction (shortening) so that the stored elastic energy can be utilized to gain maximal speed of shortening with power while performing an explosive movement. Plyometric training enhances both neural and elastic aspects of the stretch-shortening cycle, such as the squatting motions before soccer players' leap into air. "Plyometric conditioning" is a term used to describe exercise drills that consist of leaps, bounds, skips, hops, and jumps down from and up to boxes, done with rapid explosive movements (Duda, 1988). Plyometric exercise tries to combine the natural physiological SSC characteristics in the muscles with strength and power to create a truly explosive movement. Plyometrics exercise focuses on training the period of time between the eccentric and comentric phases (Brown, 2007). Plyometric training does provide such training stimuli and lias shown evidence to improve explosive actions in pubertal (Brown et ak, 1986; Matavulj, 2001). Also, these studies demonstrated the benefits of a plyometric training program in pubertal boys during a basketball season, suggesting that in season specific training might be necessary to maintain of increase the explosive actions ability.Three phases of plyometric exercise have been identified including: the eccentric phase, the amortization phase, and the concentric phase. The eccentric phase is the mental preparation phase with its duration depending upon the desired stretch stimulus. If the eccentric stretch stimulus phase duration is too long, no improvement in explosive power is observed. The amortization phase occurs when the muscle converts nervous system input into the physical work. The amortization phase is the time between the eccentric and concentric components of plyometric activity. This phase must be of a short duration to achieve the optimal power in the plyometric activity. The concentric phase occurs with the concentric muscle contraction which should be more explosive with the previous stretch occurring during the eccentric phase. The nervous system is also proposed to assess the effects of the stretch-shortening cycle to optimally prepare the muscle for the second repetition of the plyometric maneuver (Wilk et al., 1993; Chu, 1998). The three general classifications of modes of strength training are isometric, isotonic, and isokinetic training. Isometric exercises occur when muscle generates tension with no movement. Isotonic exercise is divided into concentric contractions and eccentric tensions. During both concentric and eccentric tensions, the muscle is moving. The muscle shortens with concentric contractions and lengthens with eccentric tension. Isokinetic tension occurs with the muscle generating the same tension throughout its range of motion at a constant velocity of shortening (Fleck and Kraemer, 2004; Brown, 2007). …