Explosive power is a quality that most athletes require for sporting prowess and conventional methods such as resistance and plyometric training have been the mainstay for enhancing power (Cronin and Sleivert, 2005; De Villarreal et al., 2011). Recently, however whole-body vibration or vibration exercise (VbX) has gained popularity as a form of neuromuscular training due to its time efficiency and ease of use. The most common form of VbX is achieved by standing on a commercially manufactured machine with an oscillating platform, which moves in the vertical plane or moves in a side-alternating motion about a central axis. The platform produces periodic vertical sinusoidal oscillations, where energy is transferred to the human body. Through the rapid eccentric-concentric muscle action caused by the vertical sinusoidal oscillations, this transient effect to enhance muscle performance is thought to be mediated by a rapid reflex and stretch-reflexes (Ritzmann et al., 2010), which is likely to involve the tonic vibration reflex (Pollock et al., 2012). However, other mechanisms of muscle temperature, blood flow and post-activation potentiation are enhanced following VbX (Cochrane et al., 2010; 2008; Kerschan-Schindl et al., 2001; Rnnnestad and Ellefsen, 2011) and may contribute to increasing muscle performance (Cochrane, 2013).
Most sporting movements produce eccentric and concentric muscle actions with a combination of horizontal, vertical and/or anterior-posterior ground reaction forces where lower-limb power measures are often assessed by various vertical and horizontal jump tests (Maulder and Cronin, 2005). To date, a number of studies have reported that countermovement jump (CMJ) is enhanced following acute VbX in elite field-hockey players (Cochrane and Stannard, 2005), trained recreational athletes (Bedient et al. 2009, Cormie et al. 2006, Bosco et al. 2000) although one study has reported no effect in elite athletes (Bullock et al., 2008). Furthermore, Bosco et al. (1999) observed that following acute VbX, single-leg press power increased (6-8%) across loads of 70, 90, 100, 139 kg in elite volleyball players and in male college athletes squat power increased 5.2% after receiving acute VbX (Rhea and Kenn, 2009). Given the potential of VbX as alternative exercise modality to increase explosive muscle performance the majority of the aforementioned studies have only focused on single acyclic movement performed in the vertical plane but there is paucity of research on the acute effect of VbX on horizontal jump performance. It has been suggested that further research is required with trained athletes to ascertain if acute VbX can potentiate stretch-shortening cycle activities, such as, repetitive horizontal jumping (Wilcock et al., 2009). It is well established that repetitive jump tests in the horizontal plane can provide a reliable and valid measure to assessing lower-leg power (Maulder and Cronin 2005) and that cyclic horizontal jump tests are capable of replicating power and force characteristics that occur in various athletic movements (Moresi et al., 2011). Therefore, this study proposes to address whether acute VbX can enhance explosive muscle actions in the horizontal plane by assessing bilateral horizontal repetitive jump performance.
Following VbX any changes associated with muscle performance will be dependent on the manipulation of VbX parameters, such as; vibration frequency (Hz), vibration peak-to-peak displacement (mm) and vibration duration (min or s). Although, there are a multitude of VbX combinations, a number of studies have examined optimal acute VbX guidelines for muscle performance (Adams et al., 2009, Da Silva-Grigoletto et al., 2011; Gerodimos et al., 2010; Ritzmann et al., 2013). However, there is a paucity of research on the duration of the rest interval between successive bouts or sets of muscle performance following acute VbX. Adams et al. (2009) reported that countermovement jump peak power was enhanced 1-5 mins following acute VbX and Cochrane et al., (2010) found that post-90s of VbX, the rate of force development was significantly higher compared to control and no vibration interventions. In the resistance training literature it has been documented the rest interval between sets of exercises is an important acute parameter when designing a resistance programme (Evangelista et al., 2011; De Souza et al. 2010), which can influence muscular performance (Pincivero et al. 1997; Robinson et al. 1995). Further, eliciting post-activation potentiation relies on many factors that include optimising the rest interval between the conditioning activity and outcome measure but often it has produced conflicting results (Comyns et al., 2006; Wilson et al., 2013). Similarly, little is known about the rest period when undertaking sets of explosive power movement and previous research has suggested that a closer examination of whether 1 or 2 min is sufficient to maintaining power aspects between repeated sets (Willardson, 2006).
Previous acute VbX research has focused on acyclic vertical jump performance, which has been shown to significantly increase CMJ height (Bazett-Jones et al., 2008; Bosco et al., 2000; Cochrane and Stannard, 2005; Cormie et al., 2006; Torvinen et al., 2002). However, no study has assessed the effect of acute VbX on cyclic horizontal jump performance. Therefore, the aim of this study was to investigate the acute effect of VbX on repetitive (cyclic) horizontal jumping performance and to examine the duration of the rest interval between the horizontal jump sets following acute VbX. Based from previous research that acute VbX can enhance acylic bilateral CMJ height (Bazett-Jones et al., 2008; Bosco et al. 2000; Cochrane and Stannard 2005; Cormie et al., 2006; Torvinen et al. 2002), it was hypothesised that repetitive horizontal jump performance would increase from an acute bout of VbX. As a secondary hypothesis, it was postulated that following VbX, that a larger rest period (2min) between horizontal jump sets would increase performance.
Fourteen track athlete males (age 20.8 [+ or -] 1.8 yr; height 1.80 [+ or -] 0.05 m; body mass 73.1 [+ or -] 7.5 kg)...