Comparing the Effectiveness of Whole Body Vibration and Local Vibration Exercise on Counter-Movement Jump Performance and Its Residual Characteristics in Well-Trained Athletes

Aim: This study aimed to compare the effectiveness of whole body vibration (WBV) and local vibration (LV) exercise on counter- movement jump performance (CMJ) and its residual characteristics in well-trained athletes. Material and Methods: Thirty-two male athletes (age: 22.3±3.2 years) visited the laboratory twice, 48 hours apart, and performed WBV and LV in two sessions of equal duration. Each test day had two parts (sham [0 Hz, 0 mm] and vibration treatment [50 Hz, 4 mm]), 20 min apart. LV or WBV were applied for 6×15 sec with 1 min passive rest between repetitions. During the LV, participants were asked to lie supine (2×15 sec) and then lie laterally (2×2×15 sec) such that the quadriceps muscles connected to the WBV device. WBV was applied in the squatting position at 135o knee angle. After each session, the participants were tested for CMJ for 8 min at the 1st, 2nd, 3rd, 4th,6th, and 8th min. Results: The results of two-factor repeated measures ANOVA test revealed that both WBV (p = 0.27; np2 = 0.04) and LV (p = 0.57; np2 = 0.03) and their sham conditions decreased CMJ height to a similar extent. Further, there was no statistically significant difference between WBV and LV at any measurement time point (p>0.05). Conclusion: WBV and LV were not effective methods to enhance the CMJ performance of well-trained athletes. However, WBV platform can be safely used as LV exercise equipment since no adverse effect was observed.

benefit from the vibration load to enhance performance (Drummond et al., 2014).However, local vibration (LV) may be more useful than WBV for targeting the muscles, because the muscles are directly exposed to the vibration in LV and absorption of the vibration is minimized (Drummond et al., 2014;Peer et al., 2009;Kurt et al., 2015).However, it is debatable whether LV is more effective than WBV in increasing the performance or in the treatment of injury.Another controversial topic is whether WBV equipment can be safely used for LV effectively.Kurt (2015) reported that LV is an effective exercise modality that acutely increases lower extremity flexibility compared to WBV and traditional stretching exercises.Since the subjects experienced no negative effects during LV, this treatment could be considered a safe and effective way of enhancing lower extremity flexibility.Similarly, Peer et al. (2009) reported that LV therapy can have significant acute benefits for improving flexibility and reducing perceived stiffness in healthy adults with ankle or hamstring injury.These positive effects of LV are explained by the fact that since LV is applied directly to the affected area, its impact is likely to be more concentrated than that of WBV.This may trigger a greater response in the affected muscle, including contractility of the agonist and relaxation of the antagonist, facilitating a greater range of movement than WBV (Peer et al., 2009).
There are many studies in the literature related to WBV, including squatting exercises, which have been used in general.Most of these studies used static or dynamic squat movements without external loads on the WBV plate in order to study the WBV effects on jumping performance (Abercromby et al., 2007;Cochrane et al., 2005;Turner et al., 2011;Cardinale et al., 2003;Dallas et al., 2015;Bagheri et al., 2012).In the squat movements on the WBV device, the vibratory stimulus is indirectly transferred to the body through the feet (Drummond et al., 2014;Peer et al., 2009;Rehn et al., 2007).However, the absorption of vibration energy by the soft tissues of the body during transmission to muscles while squatting on WBV device, leads to a reduced vibratory stimulus to the target muscles during jumping.It can be said that a body position in which the muscles that are active during jumping, are closer to WBV device instead of the squat position may provide more effective results while measuring the effects of WBV training on jumping performance (Cochrane et al., 2011;Drummond et al., 2014;Cochrane et al., 2005).LV may be a more useful vibration treatment for target muscles during jumping, because in LV they are exposed to a higher vibration load compared to WBV when squatting on the device (Peer et al., 2009).Therefore, this study aimed; a) to compare the effects of WBV and LV on CMJ performance levels in well-trained athletes b) whether a WBV platform like Power Plate can be used as LV equipment safely and effectively in the athletic population.We hypothesized that both LV and WBV would increase CMJ height in well-trained athletes and that the WBV platform may be used as LV equipment safely and effectively to enhance performance.

Participants
All procedures were approved by the ethics committee of a local university (approval no: 2014/162), and the study was carried out in accordance with the principles of the Declaration of Helsinki.Informed consent was provided by all volunteers participating in this study.
Thirty-two well-trained male athletes competing in sports like wrestling, judo, taekwondo, muay thai, and soccer (mean age 22.3 ± 3.2 year; mass: 73.1 ± 6.8 kg, training duration: 9.50 ± 4.27 hours/a week) were recruited for this study.The inclusion criteria for participants of the study were (i) performing physical activity for at least three or four hours per week, at least for the last three months, (ii) no injury or medical surgery related to lower extremities that could influence the test results, (iii) no functional limitation that could interfere with the test performance.The subjects had no health problems like diabetes, epilepsy, prostheses, neurological, or neuromuscular diseases requiring them to take pills regularly, which could prevent them from voluntary participation in the study.The participants were explained the testing protocol of the study in detail.Food or drinks containing caffeine or other stimulants, alcohol consumption, and rigorous physical activity were prohibited for at least 24 hours prior to the testing session for all participants.

Physical measurements
Subjects completed the research protocol on two different days (Day 1 and Day 2) with a 48-hour interval, to avoid any possible negative effects of physiological, neurophysiological and fatigue factors on the study.Each test day consisted of two sessions, separated by 20 min rest in the supine position.The first session was a sham intervention (control) (0 Hz, 0 mm vibration), and the second was WBV or LV intervention (50 Hz, 4 mm vibration).All tests were performed by the same group of researcher at the same time of the day (13:00 to 16:00) to avoid the effect of circadian rhythms on the study results.Each session started with a warm-up.Details of the day 1 (LV treatments) and day 2 (WBV treatments) protocols are explained below and in the flow chart (Table 1).Warm-up exercises: Warm up procedure included 5 min cycling on a cycle ergometer (Monark, Ergomedic-894 E Made in Sweden) at 60 rpm and 50 W. LV and WBV treatments: LV and WBV were applied using a vertical whole-body vibration platform with a standard dampening mat of 2 cm thickness (Power Plate® Next Generation PRO 5, 2x1A, 2010, USA).

Figure 1.Body positionsusedfor LV and WBV
LV treatments: In this session, the WBV platform was used as a LV source.Subjects positioned their muscles on the WBV platform in three different body postures.The target muscles were subjected to exercise for 2×15 sec with a 1 min passive rest in between.In the sham intervention session, subjects were not exposed to any vibration stimuli (0 Hz, 0 mm).During LV application, subjects were exposed to 50 Hz, 4 mm vibration.WBV treatments: Subjects performed isometric squat with bare feet at 135° ± 5° knee joint angle on the WBV platform for 6 × 15 sec with 1 min passive rest in between.In the sham intervention session, subjects had no exposure to any vibration stimuli (0 Hz, 0 mm).During the WBV application, subjects were exposed to 50 Hz, 4 mm vibration in the isometric squat position.Knee joint angle was controlled with plastic goniometer (Lafayette Instrument Europe, Richardson Products, INC., Sammons Preston J00240, 12-inch).During the squat position with vibration or no vibration, subjects placed their hands on the WBV device centralized handles for each set.

Countermovement jump (CMJ) test:
The CMJ heights were assessed using the Myotest Pro System (Myotest Sport Pro, Sweden).In the CMJ test, participants rapidly squatted down to a self-selected depth and then immediately performed a vertical jump with hands akimbo (Perrier et al., 2011).Strong verbal encouragement was provided to each participant to ensure that each jump was performed with maximal effort.The participants wore the same shoes during both sessions.Participants performed 5 CMJs with 45 sec rest intervals between successive jumps to assess baseline CMJ height.Mean score of the highest 3 CMJ was used in the statistical analyses as the baseline CMJ height.Right after each session, subjects underwent the CMJ test with maximal effort at the 1 st , 2 nd , 3 rd , 4 th , 6 th , and 8 th min to determine the residual effects of LV or WBV treatments.

Analysis of data
IBM SPSS Statistics for Windows version 22 was used for the data analysis.Normality assumption for residuals in repeated measures was tested using Shapiro-Wilk test.Two-way repeated measures ANOVA was used to assess whether changes in CMJ height after vibration treatments across time, had a different change pattern (interaction effect of Treatment × Time) compared to control treatment (no vibration).One-way repeated measures ANOVA with post hoc LSD tests were used to assess possible differences in CMJ heights between pre-test and different recovery time points of vibration treatments and control treatments.To avoid loss of statistical power, no confidence interval adjustment was performed for multiply comparisons (Perneger, 1998).Sphericity assumption was checked using Mauchly's Sphericity test.Paired Student's t-tests were used to compare the net effects of vibration treatments ("WBV -control treatment" versus "LV -control treatment") on CMJ height, at comparable time points during recovery.Statistical significance level was set at p ≤ 0.05 for all analyses.

RESULTS
Descriptive statistics of participants are demonstrated in Table 2.  Additionally, when net effects of vibration treatments were compared, no significant difference was detected in CMJ height changes (∆) between WBV and LV at any of the testing time points (Table 4).

DISCUSSION
Vibration exercise is a novel exercise modality, which is used in athletes and general population to improve muscle strength and power, improve bone density, prevent sarcopenia and falls in the ageing population, and modulate hormone secretion associated with exercise (Rittweger, 2010).The present study aimed to compare effectiveness of WBV and LV treatment on enhancement of CMJ height in well-trained athletes.The most significant finding in this investigation was that an acute session of WBV and LV reduced CMJ heights to a similar extent when compared to control (sham) treatments.These similar change patterns indicated that reductions in CMJ heights in WBV and LV sessions were resulted from isometric body postures during the treatments.In other saying, net effects of WBV and LV on CMJ were insignificant.It is difficult to explain why sham interventions led to reductions in CMJ height.These results do not support our hypotheses.However, we concluded that WBV platform can be safely used as an LV exercise equipment, since our subjects experienced no negative effects such as headaches, joint or muscle pain, dizziness, visual impairment, hearing loss, erythema, itching, and edema of the legs during vibration treatments (Dolny et al., 2008).
Many studies have reported that acute WBV leads to increase in jump height and power after vibration treatment (Cardinale et al., 2003;Dallas et al., 2015;Rittweger et al., 2003;Issurin et al., 1999;Cormie et al., 2006;Torvinen et al., 2002;Bazett-Jones et al., 2008;Bullock et al., 2008).On the other hand, a limited number of studies have reported no effect or even a decline (Rittweger, 2010;Cochrane et al., 2004;Gerodimos et al., 2010;Kurt et al., 2015;Cronin et al., 2008).The contradictory results in these studies may have been caused by load parameters of the vibration exercises such as frequency, amplitude, displacement, body position, duration of thetreatment, rest timeand training or health status of the subjects (Adams et al., 2009;Bazett-Jones et al., 2008).
It is reported that low frequency and low amplitude vibration treatment is a safe and effective exercise intervention (Cardinale et al., 2003).Cardinale and Lim (2003) argued that WBV with low frequency (20 Hz, 4 mm) increases squat jump (SJ) and CMJ height.However, WBV with high frequency (40 Hz, 4 mm) decreases squat jump and CMJ height.On the other hand, Bazzet-Jones et al. (2008) reported that 40-50 Hz and 2-4 mm WBV treatment is more effective in increasing CMJ performance compared to 30-35 Hz and 2-4 mm vibration treatment.Rønnestad (2009) suggested that WBV with 50 Hz, and 3 mm is superior to 20-35 Hz and 3 mm, in increasing SJ height.We realize that although in our study, the vibration frequency and amplitude were similar to those in the above studies, the duration of the vibration treatments was too short to achieve any performance change.A further study could be planned with 50 Hz, 4 mm, and 30-60 sec vibration treatments to compare the effectiveness of LV and WBV treatments on CMJ height.
Another important factor in the study of vibration exercises is the training status of the athletes.Some researchers argued that well-trained individuals show acute improvement in force generating capacity (Bosco et al., 1999), and untrained subjects show an acute decrease following similar vibration exercise protocol (Bullock et al., 2008;de Ruiter et al., 2003;Delecluse et al., 2005).Bullock et al. (2008)and Delecluse et al. (2005) argued that well-trained athletes, especially those accustomed to high-intensity stretch-shortening activities, have fast-twitch muscle fibers that have no scope for further performance improvement; this is due to already existing high levels of reflex sensitivity, fast-twitch fiber recruitment, and motor neuron excitability.In addition, the stiffer muscletendon units of athletes compared to untrained individuals could be another reason for no improvement, since stiffer muscle-tendon units minimize muscle length changes during WBV, reducing transmission of the vibratory stimulus tolerated body parts and resulting in a lower WBV load.This implies that performance enhancement, especially that related to speed-strength activities in well-trained athletes via WBV is more subtle than in untrained individuals.
Another way of treatment by vibration is local vibration.Formerly, local vibration was applied to the muscle belly or tendon (Issurin et al., 1999).Presently, however, segmental biomechanical muscle stimulation (BMS) devices use local stimulation rather than whole body stimulation (Peer et al., 2009).Siegmund et al. (2014) reported that BMS is useful for improvement of lower back and hamstring flexibility, as well as perceived stiffness.Issurin et al. (1994) andCronin et al. (2008) proposed that three potential mechanisms could explain the benefits of local vibration treatments: a) increase in pain threshold, b) increase in blood flow with a commensurate increase in temperature, and c) induced relaxation of the stretched muscle.
A familiarization session for the subjects was not included in the present study.Results observed in the present study may have also been caused due to lack of familiarization session.Further studies should examine the effects of LV and WBV on CMJ performance in well-trained athletes.More research is also necessary to determine the appropriate body position, frequency-amplitude of treatment, and time of exposure to the vibration.
Although no improvement in CMJ height was observed, we concluded that the Power Plate WBV platform could be safely used as LV treatment source, without adverse effects.

Table 1 .
Experimental design flowchart

Table 2 .
Descriptive statistics of participants (n=32) These findings indicated that WBV and LV had no significant extra effect on CMJ height when compared to effects of control treatments.Effects of control treatments are demonstrated in

Table 3 .
Change patterns in CMJ height after control treatments performed at 0 Hz, 0 mm vibration (n=32) *p ≤ 0.05; ∆: Reduction relative to pre-test score, min: minute; CMJ: Counter-Movement Jump; WBV: Whole Body Vibration; LV: Local Vibration; Time: Time passed after the cessation of control treatment; SE: Standard Error