Whole body vibration may help improve strength and function in patients with knee osteoarthritis and may even slow disease progression. But contradictory findings, a lack of consensus on optimal parameters, and safety issues have even WBV advocates proceeding with caution.

By Cary Groner

Vibrating on a platform may or may not sound like a fun way to exercise, but some research suggests that adding vibratory stimulus to a workout routine may augment training regimens by increasing neuromuscular activation. As reported by LER in 2010, whole body vibration (WBV) may also offer benefit to patients with neurological disorders such as Parkinson disease, multiple sclerosis, stroke, and spinal cord injury, as well as to older patients whose exercise options are limited.¹ Nevertheless, the quality of research has varied considerably, and the jury is still out regarding potential long-term risks and benefits.

A recent literature review concluded that, even in the better studies, participants exposed to WBV had similar improvements in muscle performance, balance, and functional mobility as those who did traditional exercise alone. And, though WBV may improve bone density in the hip and tibia, it apparently has no effect on the lumbar spine.²

Feasible for knee OA?

Recently, however, researchers have begun to assess the possibility that WBV may offer relief to older patients suffering from knee osteoarthritis (OA). For example, researchers at the University of Florida in Gainesville studied the effect of WBV on the physical performance of patients with knee OA and found that an acute bout of WBV training improved their ability to perform a step test and a 20-meter walk test.³

A study from Denmark, moreover, compared knee muscle strength and proprioception in older women (mean age, 60 years) randomly assigned to one of three groups—WBV exercise on a stable platform (vibM), WBV exercise on a balance board (vibF), or a control group. Muscle strength and isometric knee extension increased significantly in the vibM group versus controls, whereas proprioception (measured as a threshold for detection of passive movement) significantly improved in the vibF group compared with controls.⁴ Unfortunately, the Danish study did not compare WBV to exercise without vibration, so it isn’t clear if the results were due to the exercise itself or to the vibrating platforms.

There’s reason to hope WBV may be successful in such patients, nevertheless. Knee OA affects 12% to 16% of older adults in the US, but there are few effective treatments, so prevention is important.⁵ Older people with stronger quadriceps have a 60% lower risk of developing symptomatic knee OA than those with weak quads, but exercises intense enough to strengthen the quads may not be easy for those patients to tolerate.⁶ Because WBV has been shown to be roughly equivalent to other exercise regimens, then, it may offer such patients the chance to strengthen those muscles and decrease their OA risk. And research has shown that combining vibration and exercise can increase blood flow to the quadriceps and gastrocnemius muscles, and possibly delay muscle oxygen desaturation, versus performing similar exercises without WBV.^7,8

However, a recent stud­y in Physical Medicine & Rehabilitation found that, in a group of asymptomatic middle-aged wo­men with risk factors for knee osteoarthritis, the addition of WBV to a 12-week exercise program didn’t offer additional benefits in terms of lower limb strength or power.⁶ The paper’s lead author didn’t rule WBV out as a valid modality, nonetheless.

“There is insufficient evidence to determine ­whe­ther the addition of vibration to an exercise program will result in significantly greater improvement in lower limb strength or power than participation in the same exercise without vibration,” author Neil Segal, MD, told LER. However, Segal, an associate professor of physiatry at the University of Iowa in Ames, added, “If the use of WBV platforms improves compliance with exercise programs by making them more fun or interesting, then this may confer benefits based on increased participation.”

There is some evidence to suggest this may be the case. Although WBV evidently offers similar benefits as other forms of lower extremity strength training, in several studies the training time needed to achieve these benefits was significantly lower in the WBV group than in the exercise group (30 to 40 minutes vs 1 to 1.5 hours, respectively).^9-11 Patients who are easily fatigued or exercise averse may gain benefits from WBV that wouldn’t otherwise be available to them; however, the aforementioned studies did not focus on knee OA patient populations, so again, whether such benefits apply to those with osteoarthritis remains to be seen.

Complicating factors

The Danish study cited above,⁴ in which different vibration types produced distinct effects, hints at the difficulty in interpreting experimental results. WBV units typically provide vibration using either a rotational or vertical stimulus.² With the former, the platform rotates about an anterior-posterior axis, so placing the feet farther apart increases movement amplitude and applies force asynchronously; the effect is like standing on a teeter-totter.

Vertical-stimulus units, by contrast, have a platform that moves vertically and symmetrically, which causes simultaneous movement of the lower extremities in the same direction. Other treatment variables include frequency (Hz), amplitude (mm), duration, and vibration magnitude (g)—a measure of the imposed gravitational acceler­ation.²

Studies of WBV have used a variety of frequencies, amplitudes, and durations, and there’s no consensus about the optimal parameters needed for a given physiologic response. As a result, it isn’t clear whether the enhanced muscle activation associated with WBV is due primarily to neural factors, such as an increase in muscle spindle activation, or whe­ther other variables—say, maintaining stable posture or dampening mechanical energy—play a significant role.² Moreover, one study reported that though most studies fail to control for participants’ age or sex, these variables exert significant effects on results.¹²

In 2010, German researchers began a clinical trial of WBV compared with conventional physical therapy in patients with knee OA. The goal was to improve neuromuscular function, with the intent to both prevent OA onset and delay its progression. The researchers randomized 40 patients to two treatment cohorts (n = 20 in both groups; average age, 60 years) and treated them with one of the two modalities for one hour, three times a week, and followed them for six weeks.¹³

Although results have not yet been published, lead author Gregor Stein, MD, told LER, “We’ve found a relevant effect of both conventional physio and whole body vibration in terms of better quality of life and fewer complaints related to osteoarthritis.”

The two treatments produced intriguing differences, however, according to Stein, who teaches at the University of Cologne  in Germany.

“Patients treated by conventional physio had more strength and larger step lengths, whereas the whole body vibration group showed significantly better results in terms of fine motor skills,” he said. “These were the only relevant differences between groups, and I think this shows that vibration works by recruiting neuromuscular spindles, whereas physio improves the recruitment of muscle fibers.”

Safety

Chronic exposure to vibration is a recognized danger in the workplace setting, such as in those who work with jackhammers, and this has raised concerns about the safety of therapeutically targeted WBV, as well. Excessive vibration has been linked to disorders of physical systems (including the skeletal, vestibular, digestive, reproductive, and visual systems), and may lead to hand-arm vibration syndrome (HAVS), a secondary form of Reynaud disease that can impair blood circulation.¹⁴

The exposure thresholds that may lead to such problems are just now being elucidated, however. In a study published in 2007, researchers noted that exposure to clinical doses of WBV (up to 10 min/day, 30 Hz, 4-mm amplitude) may exceed International Organization for Standardization (ISO) standards for chronic exposure to vibration. They then compared the effects on head acceleration of both rotational and vertical devices, and reported that rotational WBV was associated with lower head acceleration. Moreover, when subjects flexed their knees 26° to 30° during sessions, acceleration decreased even further.¹⁵

“I prefer tilt [rotational] machines because you can vary the amplitude by how far you place your feet from the center,” said Harold Merriman, PT, PhD, CLT, an associate professor and general medicine coordinator in the Department of Health & Sport Science at the University of Dayton in Ohio. “If you place your feet closer together, you can dampen the forces, whereas on a vertical machine, you are limited to the designed amplitude.”

Merriman believes clinical doses of WBV are probably safe as long as clinicians pay attention to exposure variables.

“I think there’s a difference between what you get in the clinical setting and what you get in the workplace, because we’re talking about a few minutes versus hours,” he said. “At our clinic, we’ve rarely seen patient complaints, and those we do get are mild. But you have to be careful to select parameters that show the most benefit with the least amount of risk.”

He noted, for example, that increases in frequency have a greater effect on g values than increases in duration, and that such information is important in developing therapeutic protocols.

“According to the ISO, you want to keep it [exposure] under seventeen grams,” he explained. “So if you have two minutes of twenty-six hertz with a peak displacement of four millimeters, that would be just over seventeen grams, and you’d need to ramp it back a bit.”

In the 2009 systematic literature review noted earlier, Merriman and his colleague Kurt Jackson, MPT, PhD, reported that a number of existing conditions may preclude use of WBV, including hip or knee endoprostheses and acute arthritis.²

“Some of the papers did list arthritis as an exclusion criterion, and any kind of metabolic bone disease could present a problem,” Merriman said. “But I think that if someone had chronic osteoarthritis rather than an acute flare-up, WBV could still be worth investigating, because it’s a way to strengthen the muscles while putting minimal stress on the joints.”

Merriman is more cautious when it comes to artificial hips or knees, however, because one of the most common reasons for revision surgery is that the implants come loose.

“In those cases, WBV might be OK if the replacement was in good shape and the g-forces weren’t too high, but I choose to be conservative because I think there’s a risk,” he said.

WBV and immune response

In Brazil, researchers have been pursuing evidence that WBV may affect inflammatory responses and modulate T-cell mediated immunity in elderly OA patients. The researchers’ rationale is that osteoarthritis appears to involve a systematic inflammatory response as indicated by T cells and inflammatory cytokines and antibodies, which affect the function of chondrocytes. Because TCD4 cells and inflammatory markers such as soluble tumor necrosis factor (TNF) receptors may play an important role in OA-associated cartilage degradation, using WBV to reduce their proliferative responses and inflammatory marker profiles may benefit patients.

One study, published in the Archives of Physical Medicine and Rehabilitation last year, assigned 32 elderly patients with knee OA to three groups. One group did squat training with WBV, another did squat training alone, and the third was a control group that did no exercises; both exercise groups worked out three times a week for 12 weeks.¹⁶ The researchers found that the WBV group experienced significantly greater reductions in plasma concentrations of the inflammatory markers sTNFR1 and sTNFR2 (soluble TNF receptors 1 and 2), and self-reported pain than the control group. Participants in the exercise-only cohort did not exhibit similar changes.

Another study, published last year in the Brazilian Journal of Medical and Biological Research, divided 26 patients with knee OA (mean age, 72 years) into three cohorts that received treatment three times a week for 12 weeks.¹⁷ The first group did squat training with WBV, the second did squat training without WBV, and members of the control group were told not to alter their activities or begin any new exercise programs during the study.

The addition of WBV to squat training reduced the proliferative response of TCD4 cells versus control subjects, whereas squat training alone did not have any effect. This suggests that WBV may modulate T-cell-mediated immunity, minimizing or slowing disease progression in these patients.

“In whole body vibration, mechanical stimuli are transmitted to the body to stimulate the primary endings of the muscle spindles, which in turn activate alpha motor neurons, resulting in muscle contractions comparable to the tonic vibration reflex,” explained Ana Lacerda, PhD, of the Federal University of Jequitinhonha and Murcuri Valleys, Brazil, who is one of the authors of both studies.

“Our group demonstrated improvement in the functionality and self-perception of disease status, as well as improvements in the inflammatory marker profiles of elderly patients with knee OA,” she continued. “This training modality seems to modulate T-cell-mediated immunity in this population, minimizing or slowing disease progression in elderly patients.”

Future shock

Given such disparate results, the effectiveness of WBV for treating knee osteoarthritis remains open to debate. As the results of further research become available, clinicians may ultimately be able to determine which—if any—patients are most likely to benefit, and prescribe vibration therapy accordingly.

Cary Groner is a freelance writer in the San Francisco Bay Area.