Athletes embrace vibration training despite mixed reviews

If not for the Power Plate vibration training platform, Matt Hasselbeck might have showed up to training camp overweight and out of shape. Or so the Seattle Seahawks quarterback, who spent the off-season recuperating from labral surgery, suggested in the Aug. 13 issue of Sports Illustrated.

Hasselbeck told SI that performing lunges, squats, and other exercises on the vibrating platform, which theoretically stimulates neuromuscular activity, made his at-home workouts more efficient by allowing him to use less weight and perform fewer repetitions without diminishing the benefit.

Hasselbeck isn't the only elite athlete to have embraced vibration technology. Vibration platforms have become integrated, to varying degrees, into the strength and conditioning regimens of many professional and collegiate sports teams. Some football teams even have vibration platforms on the sidelines for use during games.

"The players like it, they believe in it, and it works for them, so we're going to use it," said Mickey Marotti, CSCS, director of strength and conditioning at the University of Florida, who says he uses the technology to improve flexibility. "We use it all the time: before games, during games, before practice, after practice, before workouts, after workouts."

Most trainers and strength and conditioning coaches, however, use vibration exercise primarily as an adjunct to their standard dynamic warm-up routine. The most tantalizing of the technology's potential applications-that of actually improving athletic performance by increasing muscle strength or power-has yet to find its way into the weight room or onto the playing field. In fact, even in the laboratory, researchers' attempts to quantify the effect of vibration on athletic performance have been frustrated by a decade or more of inconsistent and conflicting findings.

To be sure, some researchers have documented statistically significant effects of vibration training on strength, power, and jump height,^1-11 whereas others have reported positive trends that lacked statistical significance but may have merit from a practical perspective.^12-14 Some investigators, however, have found that exposure to vibration has no effect on performance^15-21 or, worse, a negative effect.^22,23

Despite the existence of this technology for more than 40 years, the effects of vibration on the neuromuscular system are simply not well understood. Because the precise levels of amplitude, frequency, and duration needed for optimum effect in a particular study population are not known, those parameters often vary from one researcher to the next, sometimes even within studies from a single institution. This has created an environment in which study findings are not only variable, they also cannot reliably be compared with one another. This frustrates investigators and limits the pace at which progress can be made.

"We still don't know exactly how to use vibration, so at the moment there is pretty much a 'hit-and-miss' approach in research," said Marco Cardinale, PhD, research manager at the Olympic Medical Institute in Harrow, U.K., who has published and presented extensively on the topic. "Unlike resistance exercise, where we know that if you want to get strong, you have to lift a weight that is greater than 70% of your maximum, with vibration it is still almost impossible to advise individuals on how to use it properly."

Cardinale, while part of a group led by the late Italian researcher Carmelo Bosco, PhD, was one of the first to document the positive effects of vibration exercise on neuromuscular performance. In 1999, Bosco's team found statistically significant acute increases in average velocity, force, and power during a leg-press exercise following five minutes of whole-body vibration treatment in six elite female volleyball players.¹

In a separate study, they also found that 10 days of whole-body vibration exercise increased jump height during repeated hopping by nearly 12% in active subjects, although countermovement jump (CMJ) height was not affected.² However, Bosco and colleagues also reported acute decreases in vertical jump height following seven minutes of whole body vibration in well-trained subjects,²² suggesting that there may be a point beyond which increasing the duration of vibration treatment has the opposite of its intended effect.

Positive effects

Since the turn of the century, most of the positive findings related to vibration training have measured the acute effects of limited-duration exposures. Researchers from Massey University in New Zealand performed five minutes of whole-body vibration training for 18 elite female field hockey players and found significant positive effects on CMJ height. No changes in CMJ height were observed following five minutes of exercise on a nonvibrating platform or five minutes of cycling exercise.³

Among nine male subjects, investigators from Appalachian State University in Boone, NC, also found significant increases in CMJ height immediately following 30 seconds of whole-body vibration, compared with a sham condition in which the platform did not vibrate.⁴ However, they found no effect of vibration on peak power during the CMJ, peak force during an isometric squat, or average integrated electromyography (EMG) of the vasti or biceps femoris muscles during either exercise.

"Vibration may not affect peak force, but might affect rate of force development," said Jeffrey M. McBride, PhD, an associate professor of biomechanics at Appalachian State and senior author of the study, which was published in the May 2006 issue of the Journal of Strength and Conditioning Research. "How high you can countermovement jump is related to power, not force."

Researchers from Brigham Young University also have found positive effects of vibration training in two different athlete populations. Among 38 senior (mean age 60 years) male volleyball players competing at the World Senior Games, step-jump height increased significantly following two 30-second sessions of whole-body vibration separated by one minute of rest.⁵ That study, presented at the 2006 annual meeting of the American College of Sports Medicine, did not find a significant effect of vibration on CMJ, however.

In a subsequent study presented in August at the annual meeting of the American Society of Biomechanics, researchers from the same group found that one minute of whole-body vibration exercise in 11 collegiate track athletes was associated with a statistically significant 6% improvement in peak resultant force generated during a sprint start.⁶

What would appear to be positive findings from the University of Nevada in Las Vegas⁷ may, in fact, suggest that factors other than vibration training alone contributed to the improvement in average power output observed during bench-press exercises. That study, published in February, found that the average power output for three bench-press sets was significantly higher in the group that experienced 30 seconds of vibration between sets two and three than in the group that received no vibration. Also exhibited was a trend toward an increase in peak power for the vibration condition.

However, the researchers noted that power output was significantly greater for the vibration group even before it was applied. One possible explanation is that in complying with institutional review board requirements, subjects in the vibration group knew in advance that they were going to receive a stimulus.

"The study suggested a possible psychological arousal response, in that the technology is so new and novel to them that they think it has to work," said the study's lead author, Brach Poston, PhD, who is now a postdoctoral fellow in kinesiology at Arizona State University in Tempe. "There probably is an expectation or placebo effect involved."

Mixed messages

Not all studies of the acute effects of vibration training have been positive. In fact, none of the four studies on the topic presented in June at the 2007 ACSM meeting found a statistically significant acute effect, although some did observe positive trends.

In a six-week study of 30 subjects, researchers from the University of Mississippi found that the acute and chronic effects of whole-body vibration training were not significantly different from the effects of nonvibration resistance training, but in several instances the effects were greater in magnitude.¹³ In the third week of the study, subjects who received vibration demonstrated a 2% improvement in squat-jump height, while those who did not receive vibration experienced decreases in jump height of up to 3%.

Meanwhile, researchers from Universidade Gama Filho in Rio de Janeiro, Brazil, found that seven male subjects who were experienced in resistance training were better able to withstand fatigue while doing push-ups on a platform vibrating at a high or low frequency than on one that was not vibrating. The between-group differences, though, were not statistically significant.¹⁴

Of course, in the world of professional sports, a 2% improvement in jump height might give a player a monumental advantage over an opponent, regardless of its statistical significance in the context of a study.

"You're not going to take a professional athlete in the off-season and improve his skills by 50%," said Garrett Giemont, the head strength and conditioning coach of the Pittsburgh Steelers, and an advocate of vibration training for most of his 39 years in the profession. "If you can get them to improve by 1%, you're doing great."

Still, some researchers aren't finding positive trends of any significance at all. Investigators from the University of Idaho found that exposing 13 recreational male athletes to upper body vibration prior to or during bench-press testing had no effect on mean three-repetition maximum values, in a study presented at the ACSM meeting.¹⁵

"We were expecting to see results," said Cisco Reyes, a doctoral student in health, physical education, recreation, and dance at the university and coauthor of the study. "The salesman who sold us the device said we would see 30-, 40-, 50-pound differences between someone on and off the platform."

Although some have speculated that untrained subjects may be more likely than trained subjects to experience statistically significant improvements with vibration exercise simply because their baseline strength and power levels are lower, a study from the University of Miami found no significant effect of vibration in either athletes or nonathletes.¹⁶ In that study, which was presented in June at the ACSM meeting, 30 seconds of whole-body vibration had no significant effect on CMJ height or normalized root mean square EMG at one minute or five minutes postvibration.

"We're now studying the most effective training protocols to use with this training device. Different health and fitness goals will probably require different displacements and frequencies to maximize a response," said Joseph F. Signorile, PhD, a professor of exercise physiology at the university and senior author of the study. "One thing I can tell you is that when subjects get on the machine and I turn it on, the amplitude of the EMG signal jumps up. In other words, when we apply the vibratory stimulus, we see a measurable increase in the muscle activation pattern. But to consistently translate this response into performance gains, the first thing we need to do is develop effective protocols."

Also still up in the air is the question of whether athletes can benefit from chronic use of vibration training as part of a multiweek resistance exercise program. The successful long-term use of the technology has been shown to improve strength as well as bone density in the elderly and other patient populations.^24-29

Several European research groups have found positive effects of chronic use of vibration training in athletes,^8-11 most recently demonstrated in a December 2006 Italian study of 26 volunteer female athletes.¹¹ Bilateral knee extensor strength and CMJ height and flexibility were improved to a significantly greater extent in those who received eight weeks of whole-body vibration training (three times per week) than in control subjects.

But a larger number of studies have failed to find such a positive long-term effect in athletes.^17-21 Most recently, in a 31-subject study presented at the June ACSM meeting, Spanish researchers found that performing resistance exercises on a vibration platform for 14 weeks was no more effective for female basketball players than performing the same exercises on the floor.²¹ In both groups, muscle force development during three different jump tests and squat power improved significantly.

With so many variables to control, it may be years before researchers can conclusively determine the best way to use vibration training in athletes and the kind of performance benefits to be expected as a result. But practitioners working with elite athletes now aren't necessarily waiting for those findings to be made available.

Casey Smith, ATC, head athletic trainer for the Dallas Mavericks, uses the technology regularly for warm-ups and in players who are rehabilitating from injury. Some players prefer not to use it, he says, but most do.

"I've seen improvement in recruitment of muscle, proprioception, and range of motion," Smith said. "Is it the be all, end all? I wouldn't go that far. But can it be beneficial? I think it can be."

Jordana Bieze Foster is a freelance writer based in Massachusetts and the former editor of BioMechanics magazine.

References

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