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Vibration training has historically been a tool applied in the fitness industry. But it's expanding quickly into all areas of physical medicine and rehabilitation.

Whole-body vibration (WBV) was explored as a therapy by Russian scientist Vladimir Nazarov. Nazarov tested vibration on astronauts to evaluate its impact on the loss of muscle and bone mass that occurs during extended space missions. Losing muscular strength can happen quickly in zero gravity. Losing bone density occurs at a slower rate, but astronauts are still at risk for bone fractures. Nazarov subjected astronauts to WBV training sessions prior to space travel to try and increase muscular strength and bone density.

WBV is a neuromuscular training method that uses vibrations to cause involuntary responses in muscles. Mechanoreceptors-muscle spindles and golgi tendon organs (GTO)-the sensory organs of the muscle, send information to the brain regarding muscle tension, causing muscles to contract when excited. When the GTO is facilitated, it causes muscles to relax.

When stimulated by vibration, mechanoreceptors send impulses to the brain and cause muscles to contract and relax at the rate of vibration, a phenomenon called tonic vibration reflex (TVR). This response recruits nearly 100 percent of the muscle fibers stimulated and enhances neuromuscular efficiency. Skeletal muscles contract and relax at the same frequency of the vibration. For example, in a standing squat position on a vibration platform set at 30 Hz, muscles contract and release 900 times in a 30-second session-a level of stimulation that's impossible during normal exercise.

The mechanical rationale for whole-body vibration is based on a simple formula: Force equals mass times acceleration. In traditional strength training, force production is affected by mass or increasing a load by adding weight to an exercise. In WBV therapy, acceleration is a variable that you can manipulate.

The acceleration variable increases as the platform rapidly moves up and down at a specific frequency. Acceleration is controlled by two key variables: frequency and amplitude. Research has shown that the body responds to vibrations in the frequency range of 25 to 50 Hz. In addition, research has concluded that significant vertical amplitude (2 to 6 mm) is required to generate adequate "loading" on muscular and skeletal systems.

Vibration's effects on the skeletal system include increased "loading" on the bones. Research has shown a slower progression to actual reversal of osteoporosis when vibration is used. The muscular system is affected by the enhancement of muscle recruitment. The circulatory system benefits from the rapid contraction and relaxation of muscles that work as a pump on the circulatory and lymphatic systems, which increases the speed of blood flow and lymphatic drainage. One study observed a 100-percent increase in muscle blood volume in the calf and thigh following treatment.

A significant body of research has shown a range of applications for WBV, such as improving balance, proprioception and circulation, and knee and neuromuscular rehab. WBV research also observed results for posture following stroke, low-back pain, range of motion and osteoporosis.

Contraindications associated with vibration therapy include pregnancy, hip or knee implants, recently placed screws, pins, bolts or spirals, acute hernia, discopathy or spondylitis. In addition, you shouldn't apply vibration therapy with people who have a pacemaker, serious cardiovascular disease or any heart condition, acute thrombosis or blood clots, epilepsy, serious diabetes, a history of detached retinas, advanced arthrosis, arthropathy and advanced rheumatoid arthritis.

Vibration platforms include motors with counterweights that cause force in all directions, which makes the platform vibrate as the motors spin. Single-motor platforms cause vibration in all three planes of motion. Dual-motor units have synchronous motors that limit side-to-side and forward-to-back motion, so most of the motion is vertical. Platforms that don't create significant vertical motion (amplitude) can't create the necessary loading on the body that's required for results.

Vibration isn't intended to replace existing therapies. But given the potential benefits of "acceleration" training, incorporating WBV can enhance and augment standard exercise and rehab programs.

This Clinician's Guide was written by J. Stephen Guffey, PT, EdD, owner of Physical Therapy Plus in White Hall and Pine Bluff, AR.