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Case Study 2: Vibration and Muscle Strength and Power

This is an excerpt from Evidence-Based Practice in Exercise Science by William Amonette,Kirk English & William Kraemer.

Charity is a university strength and conditioning coach. Recently, a professor in the school's exercise physiology program acquired several vibration plates for a planned research study. The vibration plates are housed in the athletic training facility and are available to the athletes. Charity heard about training with vibration plates at a national conference she attended recently; the presenter described a variety of upper and lower body exercises that could be performed on the plate and anecdotally claimed that such training results in noticeable performance improvements in athletes participating in a variety of sports. As an evidence-based practitioner, Charity realizes that although the vibration plate presentation was compelling, she needs to search the literature to determine what kind of scientific support exists for using vibration plate training as a modality to improve physiological and athletic performance.

Background

Vibration is thought to enhance acute neuromuscular performance via the stimulation of Ia afferent nerves, which effects a myotatic reflex contraction (Abercromby et al., 2007). Acutely, vibration improves maximal force and power output during concentric contractions; this facilitative effect is greater in elite athletes than in amateurs (Issurin & Tenenbaum, 1999; Liebermann & Issurin, 1997). However, vibration is ineffective when applied acutely to promote recovery or improve subsequent running performance after a strenuous exercise bout in highly fit runners (Edge, Mundel, Weir, & Cochrane, 2009). In competitive athletes, routine vibration training can increase strength, jump performance, and flexibility (Fagnani, Giombini, Di Cesare, Pigozzi, & Di Salvo, 2006), as well as improve proprioception and balance after anterior cruciate ligament reconstruction in comparison to a conventional rehabilitation program (Moezy, Olyaei, Hadian, Razi, & Faghihzadeh, 2008).

Charity currently employs evidence-based strength and conditioning programs with her athletes; these programs consist largely of resistance exercise - both traditional strength and explosive Olympic weightlifting exercises. Thus, to make a valid comparison in her athletic population, Charity should compare the effectiveness of vibration training to that of traditional resistance exercise. Given the limitations of vibration training (cost, availability, spatial restrictions), only if vibration training (either alone or in combination with traditional training) proves superior to traditional training would it be prudent to incorporate it on a large scale. Thus the evidence-based question is as follows.

In trained athletes, does vibration training, either alone or as an adjunct to resistance exercise, elicit improvements in muscle strength or power that are superior to those realized with traditional resistance training?

Search Strategy

Typing "vibration" into PubMed yields a list of MeSH subheadings; we select "vibration training." This returns 1141 studies. Activating the Age filter (Adult: 19-44 years) and Language filter (English) reduces this number to 377. Next, we add "AND athletes" to the search string ("vibration training AND athletes"), which returns 20 articles. Scanning these abstracts reveals 3 papers directly related to the chronic effects of vibration training (Delecluse et al., 2005; Issurin, Liebermann, & Tenenbaum, 1994; Preatoni et al., 2012). Of the 17 articles not included, most are acute studies and several others examine the effects of vibration on postworkout recovery and postsurgical rehabilitation outcomes; another study was excluded because it is not clear what exercise the control group performed.

Discussion of Results

The three articles reviewed are summarized in table 15.2. Preatoni and colleagues (2012) evaluated the effects of vibration training alone and in combination with traditional resistance training in 18 national-level female athletes (12 soccer and 6 softball athletes, with equal proportions in all groups). Subjects were randomized to one of three groups: (1) whole-body vibration training group, (2) traditional strength training group, and (3) combined whole-body vibration and strength training group. All training was performed during the winter preparatory period and in combination with other sport-specific field training such as speed drills, aerobic work, and technical and tactical skill practice. The periodized resistance training program was performed 2 days per week for 8 weeks; for the first week it consisted of six sets × six repetitions of squats performed at body weight with vibration (vibration group), at 60% 1RM (strength training group), or 30% 1RM with vibration (combined whole-body vibration and strength training group). Every 2 weeks, the external load was increased 6% (for the strength training group) and 3% (for the combined whole-body vibration and strength training group); greater intensity for the vibration group was achieved by increasing vibration frequency 5 Hz every 2 weeks (frequency was also increased for the combined group). Outcome measures included isometric strength (leg press); dynamic force, velocity, and power (explosive leg press with loads of 100% to 200% body weight in 20% increments); and power and power endurance (vertical jump and continuous 15-s vertical jumps, respectively). Training increased isometric strength (main effect, P = 0.02) with no differences between groups. No changes were observed for any parameter of the explosive leg press test. Performance on both vertical jump tests increased with training (main effect, P < 0.002), but there were no differences between groups. Maximum jump height (vertical jump test) and mean jump height and power (continuous 15-s vertical jump test) were increased only in the strength-trained group. The investigators also evaluated the characteristics of the vibration device (i.e., frequency, amplitude, and acceleration) and found variations up to 20% from the selected value; this was particularly true at higher frequencies. On the basis of other published data (Blottner et al., 2006; Mulder et al., 2008, 2007; Rittweger et al., 2006), the authors conclude that vibration exercise can elicit similar or improved outcomes compared to traditional strength training only when similar external loads are used; that is, they attribute the lack of an effect in their study to the lower external loads lifted by the combined vibration + strength training group (Preatoni et al., 2012).

Delecluse and colleagues (2005) examined the additive effect of a whole-body vibration training program over 5 weeks in 20 sprinters. Male and female sprinters (mean 100 m times: female = 12.46 ± 0.59 s, male = 11.45 ± 0.42 s) were randomly assigned to either a vibration or a control group. Both groups maintained their conventional training program, which consisted of intervals (10-60 s), speed training (two or three sessions per week with efforts near race pace), speed drills (two sessions per week), plyometric drills (one session per week), and explosive resistance training (three sessions per week) at 75% to 95% 1RM (three to five sets × two to five repetitions). In addition to their typical training, the vibration group completed three sessions per week of unloaded static and dynamic leg exercise on a vibration platform. The exercises employed were high squat, deep squat, wide stance squat, single-leg squat, lunge, and heel raise. The vibration program was implemented progressively through increases in the duration of vibration time and concomitant decreases in the rest periods; vibration amplitude (displacement) and frequency were also increased over the 5-week program. The study was conducted during the precompetitive phase of training. Outcome measures included strength (isometric and isokinetic knee extensor-flexor), maximal knee extension velocity (at 1%, 20%, 40%, and 60% of maximum isometric force), vertical jump, starting parameters (start time, horizontal start velocity, and horizontal start acceleration), and maximum velocity in a 30 m sprint. There were no changes in either group after the 5-week training program, nor were there any interaction effects or differences between groups posttraining.

Issurin, Liebermann, and Tenenbaum (1994) examined the effects of vibration training in 28 young male athletes who regularly participated in a wide cross section of club or varsity sports such as judo, swimming, volleyball, tennis, soccer, track and field, and cycling. Subjects were randomized to one of three groups: (1) upper body strength training with vibration and lower body flexibility training, (2) upper body strength training and lower body flexibility training with vibration, and (3) a calisthenics - basketball game control. The training program, which was conducted three times per week for 3 weeks, consisted of a ~10-min warm-up, a single upper body strength exercise (seated bench pull: six sets × six repetitions at 80% to 100% 1RM performed to failure), and ~20 min of specific static and ballistic stretching of the upper leg musculature. The program was performed by both experimental groups; vibration was added to either the upper or lower body activity according to group assignment. Outcome measures included strength (bench pull 1RM) and flexibility (two-leg split distance and sit and reach distance). Collectively, 1RM strength and both flexibility measures increased with training (main effects); there were also differences between groups for each outcome (group × time interaction effect). Unfortunately, the authors did not provide statistical contrasts between groups (e.g., strength training vs. strength training with vibration) to elucidate the between-group differences; because of the influence of the control group (which changed very little for any measure) on both main and interaction effects, it is difficult to interpret the study findings.

Luo, NcNamara, and Moran (2005) published a review evaluating the effects of vibration training on muscle strength and power, examining the effects of both chronic and acute vibration training. In 2005, only three papers had been published on the chronic adaptations to vibration training; of these, only one study employed trained athletes as subjects and has already been discussed (Issurin et al., 1994).

Conclusion and Strength of Evidence

There has been an explosion of literature regarding whole-body vibration in recent years. Some studies have been well conducted; others are poorly designed or uncontrolled, leading to erroneous or equivocal conclusions. There is still minimal understanding of the appropriate frequency, amplitude, direction, and length and mode of exercise needed for positive adaptations to vibration training. Despite the widespread use of vibration in athletic and private training settings, the evidence at the current time does not suggest that it is a strong tool to improve strength in athletically trained populations, although there is evidence for use in other populations.

There is level B evidence to refute the use of vibration training as a stand-alone or adjunct training method to increase muscle strength or power in athletes, as it is not demonstrably superior to traditional resistance exercise.

Program Recommendations

Although evidence supports vibration as a tool to improve strength and power in untrained populations, the data do not support its use to improve performance in athletes versus traditional strength methods. There is some evidence to support its use as a tool to acutely potentiate a power response; thus if Charity chooses to implement vibration, based on the literature it should be used as a postexcitatory potentiation tool. In general, Charity should continue training her athletes using traditional strength and conditioning programs but continue to watch the literature for emergent studies and protocols.

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