The Effects of Two Different Whole-Body Vibration Frequencies on Isometric Strength, Anaerobic Performance, and Rating of Perceived Exertion

IntroductionAnaerobic performance consists of anaerobic power and anaerobic capacity, 2 of the most important performance criteria of sports requiring short-term explosive effort (Issurin and Tenenbaum, 1999; Ozkan et al., 2009). Studies done in the last decade showed that there is positive correlation between anaerobic performance and leg strength (Kin-Ðsler et al., 2008). According to Arslan (2005), performance in basic motor skills such as running and jumping is highly related to leg strength; moreover, leg strength is one of the key components in modern sports.It has been reported that both recreational and competitive athletes preferred modern strength training methods to traditional ones until the 1980s (Wirth et al., 2011; Cardinale and Erskine, 2008). Therefore, the number of athletes who use vibration-training methods is increasing (de Ruiter et al., 2003a).Although the neuromyogenic mechanism of vibration applications is not fully understood, stimulation of muscle spindles, one of the sensory receptors of muscles, by the mechanical vibration may be one of the possibilities of this mechanism. This stimulation leads to the activation of the alpha-motor neurons and initiation of muscle contractions comparable to the previously described tonic vibration reflex (Delecluse et al., 2003). Although this information mostly explains the physiological mechanism of the vibration training, there is no consensus on which combinations of application variables (such as frequency, amplitude, application and resting periods, number of sets, contraction type [dynamic or static], use of additional load or body weight, and body position) are safest and most effective (Paradisis and Zacharogianis, 2007; Cardinale and Lim; 2003; Delecluse et al., 2003).Cardinale and Wakeling (2005) stated that frequency, amplitude, and application duration in vibration training defines the intensity of the vibration application. Frequency and amplitude of vibration exercises are 2 of the most commonly discussed variables in whole-body vibration training (WBVT). Generally, low-amplitude and high frequency application is accepted as a safe and effective method for improving musculoskeletal fitness (Torvinen et al., 2002a; Paradisis and Zacharogiannis, 2007; Rehn et al., 2007). In contrast, Cardinale and Lim (2003) argue that low-frequency and low-amplitude vibration application is also an effective method and state that high-frequency applications can cause neuromuscular fatigue, activating inhibitor mechanisms that impair performance. Some researchers also stated that to improve different motor skills, different frequencies and amplitudes should be applied (Gerodimos et al., 2010). According to Ronnestad (2009), the optimal frequency for improving average peak power and vertical jump height is 40-50 Hertz (Hz). However, 4-8 Hz has been stated to be the optimal frequency for flexibility improvement according to Gerodimos et al. (2010).Furthermore, it has long been known that biological tissues also resonate with different frequencies. Internal organs, eyes, and muscles resonate at 8, 20, and 7-15 Hz, respectively (Mester et al., 2006). In some clinical studies, frequencies lower than 20 Hz were found to be harmful for human health (Schuhfried et al., 2005; Gusi, 2006; Paschold and Mayton, 2011). For this reason, the preferred frequency for vibration training should not be lower than 20 Hz. Torvinen et al. (2002) showed that 4 months of WBVT with nonathletic adults (21 men and 35 women aged 19-38 years) increased isometric lower limb extension strength. In contrast, Delecluse et al. (2005) found no increase of knee-flexor strength after 5 weeks of progressive WBVT with well- trained sprinters (6 women and 4 men, aged 17-30 years).Many studies have shown that vibration training increases jump and anaerobic performance (Bosco et al., 1998; Torvinen et al., 2002; Wilcock et al., 2009; Paradisis and Zacharogianis, 2007). …