Jan 29, 2015Shaking It Up
As whole body vibration continues to catch on in weightrooms and with athletic trainers, researchers are shedding new light on how it works and what its benefits are.
By David M. Bazett-Jones
David M. Bazett-Jones, MS, ATC, CSCS, is a Doctoral Candidate at the University of Wisconsin-Milwaukee and is actively involved with the Athletic Training Program. He has published several studies about whole body vibration and how it relates to athletic performance and rehabilitation. He can be reached at: [email protected].
When first presented, the concept sounds a little crazy: Perform exercises while standing on a vibrating plate to help you work out more efficiently or as part of a rehabilitation program to help you return to play faster. But whole body vibration (WBV) is doing just that. And its growing popularity over the past decade has athletes, strength coaches, and athletic trainers wanting to know what the buzz (both figuratively and literally) is all about. The growing curiosity about WBV has been a double-edged sword. On one hand, there are more published studies on how it works and its possible benefits. In the first 10 months of 2010 alone, more than 80 research articles on WBV were published.
On the other hand, there are more unsubstantiated claims about its benefits than ever before. An Internet search of the term “whole body vibration” results in almost 200,000 hits. Plus, as the number and type of WBV devices available continues to grow, the practitioner’s decision on which devices to use becomes that much more difficult.
With so much to sort through, athletic trainers and strength and conditioning coaches face an uphill battle in deciding if, how, and with whom to use WBV. This overview of the most recent research and some practical applications of WBV in the athletic training room and the weightroom should help cut through the clutter.
HOW IT WORKS
Let’s start by defining vibration, which is a mechanical stimulation characterized by oscillatory or wavelike movement. It can be applied directly to muscles and tendons or indirectly through the use of vibrating platforms, dumbbells, cables, or even entire vibrating workout machines.
Vibration consists of frequency, amplitude, and acceleration. Frequency, in hertz (Hz), measures the number of cycles of the oscillation per unit of time. Amplitude, in mm, is the distance between the minimum and maximum displacement values of the oscillation. Together, frequency and amplitude determine the acceleration of the vibration, often calculated in “g”s (one g is the acceleration due to gravity). Most vibration platforms–the most common way to use WBV–provide frequencies of 20-50 Hz, amplitudes of 0.5-5 mm, and accelerations of just over one g up to 10.
So what happens when an individual stands on a vibration platform? Imagine for a minute that the athlete’s body is a rigid object. During the upward phase of the vibration oscillation, their body accelerates along with the platform until the platform reaches its peak. The body would then become airborne until it again contacted the vibration platform, at which time an impact force would occur between the body and the platform. These impacts could be harmful.
Because the human body is not rigid and our muscles and tendons store and release energy to help it act more like a spring, it can safely deal with these forces. Muscles have shown specific properties useful for dampening vibration, one being the linkage design of the musculoskeletal system, which allows a vibration to be transmitted through the legs to the trunk and dampens the vibration as the legs are bent. This is why an individual standing on a vibration platform with locked knees feels the vibration in their head (not a nice feeling), which goes away when they bend their knees.
Muscle activations and contractions occur as a result of each vibration. It’s commonly said that WBV causes thousands of separate muscle contractions during a typical training session. However, this theory has not been substantiated through research. A better description of muscle response to WBV is that they go through entire cycles of eccentric (lengthening) and concentric (shortening) contractions during a WBV workout. Again, this can be felt when one stands on a platform with knees bent–the quadriceps muscles feel tight like they are constantly contracting (like contracting a muscle isometrically).
There have been many claims about the mechanisms of WBV, the most common of which is called the tonic vibration reflex. This reflexive muscle contraction has only been found in a relaxed muscle during direct tendon vibration. No studies have yet linked tonic vibration reflex and WBV.
Tendon vibration does indeed elicit increased muscle spindle contraction. However, it also stimulates the Golgi tendon organ, causing antagonist muscle contraction. Since a muscle cannot contract and relax at the same time, other mechanisms may be present.
Those mechanisms could be reflex enhancement or post-activation potentiation. Or it may be that a complex cascade of effects is present and a dampening muscle absorbs energy and generates heat, resulting in increased muscle temperature and blood flow.
One thing is certain. The mechanism of WBV is multifaceted and will require much more study, even though researchers are already making headway on the ins and outs of how exactly it works.
WHY USE WBV?
By now, numerous studies on WBV and its effects have been conducted and published. Here are some of the highlights on the benefits of using WBV:
Vertical jump. The recent surge in WBV began in 1998 after a study by Bosco et al. reported enhancement of vertical jump height with its use. Since then, acute increases in vertical jump (up to nine percent) have been reported by many other authors. Note that these effects may be gender specific, with our group reporting improvements for women but not men. These results may also be specific to training level, with the largest improvements seen mainly in those who are less trained.
Strength gains. Using WBV to promote muscle strengthening has also received continued attention over the past decade. In a 2010 study, Marin & Rhea compared the effects of acute (single-use) and chronic (repetitive use over time) WBV and found that while acute exposure had negligible effects, chronic exposure was consistent with the effects of traditional resistance training. This finding is important because WBV training can typically be performed in much shorter durations than traditional resistance training. More so, individuals who have restricted motion due to age or injury may benefit the most from static WBV exercises to increase strength or lean body mass. The researchers further reported that WBV programs that included both static and dynamic exercises were more effective than static alone.
Muscle warmup. Since muscle temperature increases when muscles absorb vibrations, WBV may be effective as part of pre-competition warmup routines. Athletes generally complete some sort of pregame preparation for this very reason–to “warm up” their muscles. Published studies of golfers and softball players who used WBV during their warmups showed improvements in golf club speed and bat speed during competition.
Flexibility. Performing stretching exercises while on a vibration platform may help athletes limber up a little more. Research has reported that even simply standing on a WBV platform for five minutes improved flexibility by over 16 percent. A recent study saw a 22-percent increase in flexibility with four weeks of static stretching during WBV but only a 14 percent increase when participants did static stretching alone. Furthermore, the group that did static stretching combined with WBV was able to maintain a significant (11 percent) enhancement in flexibility even after a three-week cessation period.
A note of hesitation must also be presented here. Many club and professional sports teams are using WBV on the sidelines during competition, similar to the use of a stationary bicycle, to help keep athletes warmed up. This raises the question, “Is there such a thing as too much WBV?” The opportunity for repetitive exposures and intensity of muscle activation that WBV elicits leads me to hypothesize that excessive use during competition may actually cause greater fatigue, possibly leading to greater injury risk. But research into this question is sorely needed.
While acute performance enhancements have been documented in applications like jumping, WBV has not been shown to improve sprint or agility performances when used as part of a warmup. This may be because the task of sprinting involves the entire body for a longer duration than a movement like jumping.
Over time, it’s possible that an athlete’s sprinting may improve, but even after eight months of WBV training, no chronic benefits on agility have been documented. Overall, it seems reasonable to assume that a minute or two of WBV may improve performance of a short, explosive task.
Does WBV help fight obesity by improving body composition? While lean body mass has been reported to improve following 10 weeks to 18 months of WBV training, these benefits have mostly been seen in the elderly or untrained. Given the limited number of studies on this subject, WBV seems effective in improving body composition in the elderly, obese, or untrained. However, it may not be effective for young or active individuals.
Does WBV have a cardiovascular effect, thus helping to improve heart health? Recent research indicates that the answer is no. It seems that a semi-squat with WBV is no more taxing to the cardiovascular system than without it. Until further research shows otherwise, it looks like bikes, treadmills, or elliptical machines are still integral pieces of equipment to improve health.
WBV FOR REHAB
Using WBV in a rehabilitation setting is a fairly new endeavor, but rehab patients can benefit from WBV in multiple ways. In fact, I would venture to say that the application of WBV to rehabilitation and populations with limited mobility is the future of WBV. First, since WBV has been shown to increase muscle temperature faster than cycling, it may function as a good pre-rehabilitation warmup.
The increased blood flow that occurs with the use of WBV may positively influence swelling and inflammation at a non-acute injury site, but this hypothesis has not been adequately explored via research. WBV might also be beneficial in rehabilitation by helping to ease pain, possibly by over-stimulating pain receptors in a way similar to the Gait Control Theory (e.g. rubbing your elbow after you hit it).
Interestingly, vibration itself has long been linked to low back pain in truck drivers and others in similar lines of work. However, it seems that when WBV is utilized as exercise intervention, those with low back pain experience a drop in pain level. Differences in the vibration application, frequency, and duration, or the posture during exposure could account for this conflict. WBV has even been reported to aid in pain reduction in fibromyalgia–a condition generally accompanied by constant pain.
Other specific applications of WBV for rehabilitation have been reported in literature as well. One study reported that patients with knee osteoarthritis saw improvements in muscle strength following eight weeks of vibrating platform work and slightly better balance. Following a total knee arthroplasty, patients who received four weeks of WBV-based rehabilitation showed similar improvements in strength and function compared to traditional progressive resistance exercise protocols.
Anterior cruciate ligament reconstruction patients have reported significant improvements in proprioception when using WBV therapy instead of a conventional rehabilitation program. Improvements were also seen in patients’ non-operative knees as well, demonstrating a possible crossover effect. According to one study, these improvements may be due to repetitive stimulation of the various receptors that provide information needed for proprioception. All in all, WBV may provide rehabilitation professionals with a unique tool to provide multiple benefits within a limited time frame.
Before jumping into WBV training with athletes or clients, it is important to do a number of things. Performing a pre-intervention physical and taking a medical history should be at the top of the list. If you don’t feel that doing so is within your scope of practice, have the individual get a written letter of clearance from their physician for WBV use.
Some WBV manufacturers provide lists of risks associated with use, but there may be some unknown risks and you should use your best judgment when evaluating an athlete or rehab patient for WBV use. I have had individuals with epilepsy and diabetes (two common manufacturer contraindications) use WBV and they’ve experienced positive results, but that doesn’t mean all epileptics and diabetics will.
There may also be unknown risks. Two recent case reports of serious reactions to WBV drive home the importance of this point. One patient had a severe reaction because of asymptomatic kidney stones, and another patient experienced a serious case of vertigo. We also don’t know the long-term, chronic use effects at this time, only the effects of WBV on spinal and circulation pathologies from the industrial setting, which are much longer durations. Until we can further understand the long-term effects of WBV, unsupervised or unlimited use (e.g. at home) should be discouraged.
Always observe individuals using WBV closely, especially in cases where medical or family history increase risk for complications. Finally, athletes and other patients should be fully informed of the benefits and risks of using WBV. This should include explaining that we don’t know all of the benefits nor all of the risks associated with WBV, and that no research on long-term daily use exists.
Using WBV as an acute performance enhancer may require some trial and error on your part when designing a program–and it may differ from person to person. In general, 30 or 50 Hz seems to be effective for acute performance enhancement. You might also want to try pairing low frequencies (30 Hz) with low amplitudes (2 mm) and high frequencies (50 Hz) with high amplitudes (4 mm), according to researchers. It’s important to note that greater rest periods (at least two minutes) between sets are more beneficial to acute performance enhancement than shorter rest times (less than one minute)–especially when multiple (at least six) WBV exposures are used in one session.
As for which exercises to perform, a WBV program should resemble a traditional resistance training periodization program. Since neuromuscular adaptations are likely to account for many of the enhancements seen with WBV, periods should be short and change often, approximately every two weeks. Exercises should progress from easy static moves like a semi-squat to more difficult static moves like a squat to 90 degrees, then to more dynamic exercises like a full squat.
Some individuals may find static exercises more challenging than dynamic exercises, so this progression can be adapted to individual needs. Advanced athletes may want the extra challenge of adding weight to their WBV exercises as well. Exercises in the seated or lying positions should only be performed when absolutely necessary and only in younger or athletic populations.
Tweaks to a program in search of optimum benefit might include increases in duration, then frequency, then amplitude in order to constantly provide adequate stimulus to the neuromuscular system. You can even use electromyography (a way to evaluate the electrical activity produced by skeletal muscles) to determine the optimal vibration frequency for each individual. Reducing the amount of rest between sets may also increase the intensity of the WBV workout.
The duration of WBV work should not exceed 15 minutes of actual vibration time per session, and this time should be much shorter if an athlete is using WBV on a daily basis. Finally, a “washout” period in which an individual discontinues WBV training for a few months to participate in other forms of exercise may be important for long-term safety and avoiding training plateaus.
WBV is an exciting new exercise and rehabilitation modality that may offer substantial benefits to many people, especially athletes. Scientific evidence is available for many of the claims made about WBV, but further research is needed for others. Those who are untrained or elderly have the most to gain from WBV interventions.
At this point, the potential benefit of WBV must be coupled with thinking about the potential risks and unknown long-term effects. However, with taking proper precautions and using logical progressions, it seems that WBV is safe for most individuals.
To view full references for this article, go to: www.Training-Conditioning.com/References.
To see some of the author’s video examples of WBV exercises, go to: www.Training-Conditioning.com and click on “Video Library” in the top left-hand corner of the page.