Academic journal article Journal of Physical Education and Sport

Relationship of Mechanical Properties between Vertical Jump (SJ) and Concentric Test in a Three Angle Isokinetic Machine of Lower Extremities

Academic journal article Journal of Physical Education and Sport

Relationship of Mechanical Properties between Vertical Jump (SJ) and Concentric Test in a Three Angle Isokinetic Machine of Lower Extremities

Article excerpt

Introduction

Several researchers studied the reliability and validity of measurements in isokinetic dynamometers of self-made constructions, as well as in standard machines of various companies. Also measured the reliability of these devices through various parts of the body, such as i.e. upper & lower limbs, trunk, or several individual muscles and joints (Caiozzo et al. 1981; Martin et al. 1993; Lands et al. 1994; Wilson et al. 1997; Dowson et al. 1998; Blazevich and Jenkins 1998; Walshe et al. 1998; Kubo et al. 1999; Li et al. 1999 Paasuke et al. 2001; Gissis, 2003).

Vertical jump ability is an important and specialized form of training in many disciplines. Many researchers have addressed the plyometrics (Drop Jumps) and their research results offered a lot to the development of the coaching process (Bosco and Komi 1979). It lias been shown the relationship of vertical jump capacity with high explosive capability. Jumps are compound movements, where achieved high reaction forces in conditions of high coordination of movement. The power is developed based on energy storage mechanism in elastic items, during the eccentric contraction and release during concetric (Steben and Stcbcn. 1981; Bosco andPittera, 1982; Clutch et al. 1983).

Literature suggests a specific set of performance testers vertical jump, which is the indicator of the jumping ability of the test (Garcia-lopez et al., 2005). This test package consists of the vertical jump from a standing position without swinging arms and the knees flexed 90° [Squat Jump (SJ)], the vertical jump with counter movement without swinging arms and upright [Counter Movement Jump (CMJ)] and the vertical jump performed after the body drop from a specific height [Drop Jump (DJ)], (Bosco et al., 1982; Liu et al., 2009; Pereira et al., 2009; Korff et al., 2009; Lazaridis et al., 2010). A stretch-shortening cycle (SSC) can be defined as an active stretch (eccentric contraction) of a muscle followed by an immediate shortening (concentric contraction) of that same muscle. In human skeletal muscle SSC gives unique possibilities to study normal and fatigued muscle function and it's found in most sports. Although explosive power lias been extensively studied in lower body activities such as vertical jumping (Bosco et al., 1982; Tsatalas et al., 2010).

All kind of exercise including individual and team sports, share one common feature, that is the natural stretch and shortening cycle of eccentric-concentric, or concentric-eccentric contractions at sub maximal or maximal intensity. It is well known that during the eccentric phase of SSC, produced larger forces than the concentric (Kues, Mayhew 1996, Enoka 1996). Although, experimental models of exercise with eccentric contractions are well documented in terms of the time course, the muscle damage, soreness and stiffness (Norrbrand 2008, Chapman 2007, Lavender 2006).or the protective effect against muscle damage (Chen 2007), much less is known about how mechanical and neural factors interact during exercise training with high intensity eccentric contractions close to 90% of the maximal eccentric force.

Eccentric programs are recognized as particularly effective in increasing maximal strength (Duclay et al. 2008). The development of isokinetic dynamometers allowed for application of an accommodating resistance to the muscles, resulting in eccentric exercise at a constant movement velocity. Schmidbleicher & Gollhofer (1982), argue that the differentiation of jump height in relation to the height of drop is a result to a technique modulation during performs the vertical jump. If the drop height increase and the technique of jumping is not brought under control, the participants are likely to make more traffic down the moment of landing. Bosco et al. (1979), argue that a depth of jump after falling height 20-40 cm high positive values observed in performance during the concentric phase of contraction and when the jump is executed from greater heights, such as after a drop height of 40-60 cm, maximum values are observed both in the eccentric phase and in service during the concentric phase of contraction. …

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