The days of dissecting the human muscular system into a collection of isolated, independently acting muscles are in the past. When it comes to our daily muscular demands, those that ultimately determine our degree of physical and often mental exhaustion at the end of each day, strengthening muscles in single planes of motion no longer makes sense.

When was the last time anyone accomplished anything functional by repeatedly flexing and extending their knee while the rest of the body remained stationary? Or better yet, when did human movement involve abducting and adducting your hips while you sat in a chair?

While I am not suggesting that these exercises do not provide value, they simply fail to succeed at preparing the body, or the nervous system that operates it, for the actual activities we engage in each day. This realization is behind the mass movement in the physical therapy field toward abandoning the monotonous, robotic movements that have been prescribed for so many years and embracing what has come to be known as functional strengthening.

Functional strengthening involves exercises being performed with body weight, cables, or other forms of resistance through movements designed to reproduce functional activities of our daily lives (e.g., pushing, pulling, squatting).

With origins linked to sports performance enhancement and neurological rehabilitation, functional strengthening theory tells us that in order to continue to efficiently and effortlessly carry out the many complex interactions that our muscles undergo on a day-to-day basis, there must be specificity in the way they are trained.

This approach emphasizes the importance of coordinating the complex interactions of both the neural and muscular components of functional activities. This is the incomparable value of this approach and it is accomplished primarily by enhancing our nervous system's ability to communicate; in other words, taking advantage of its "neuroplastic" capabilities.

Neuroplasticity

The neuroplasticity model of the nervous system, arguably the biggest scientific breakthrough of the 20th century and a subject of many recent studies, explains that through repeated exposure to a given activity, no matter how old we are, our central nervous system is capable of reorganizing itself to meet our demands. This reorganization process has been hypothesized to be the result of increased synaptic transmission speeds through increasingly dense neural networks. In the paraphrased words of Donald O. Hebb, a pioneer in nervous system learning theory called Hebbian Learning, "Neurons that fire together, wire together."¹Through this reorganization process, the ability to carry out the activity with greater accuracy, less energy expenditure and faster speed is improved.

As this concept translates into the functional strengthening approach, the more frequent and precise a specific functionally relevant exercise is performed, the faster, stronger and more efficiently that movement can be reproduced when needed. Thanks to functional brain imaging, neuroplastic theory's validity is increasing rapidly and has begun to change the way we look at patients' potential to respond to physical therapy.

As a result, our increased desire to maximize patients' functional and recreational status has forced us to look toward newer methods of achieving functional strength. One method, referred to as vibration training, is rapidly emerging and has distinguished itself due to its amazing ability to directly "tap in" to the nervous system. Capable of safely reproducing compound involuntary muscle contractions with repetition rates never before seen, vibration training may be the next great leap in rehabilitation.

Pivotal Vibration Training

There are currently two types of vibration training platform systems on the market today. The first system, referred to as lineal, linear or vertical, moves straight up and down and predominantly stimulates muscles that work along the sagittal plane. The second type of system, referred to as a "pivotal" or "alternating" system, moves in a teeter-totter direction and engages muscles that work along the frontal and transverse planes.

While both have significant value, when considering the reciprocal nature of human locomotion and the need for training specificity, pivotal vibration training provides the greatest potential to maximize an individual's functional capabilities.

Created in an effort to combat bone density loss, the first pivotal vibration platform was created in Germany in the 1990s. This platform system, referred to as the Galileo, is behind the majority of the research that exists today in support of vibration technology for rehabilitation purposes.^2-4

Pivotal vibration training involves anything from simply standing to performing complex functional strengthening exercises on a moving pivotal vibration platform. When performed correctly, pivotal vibration training allows the body to undergo thousands of reciprocal muscular contractions in minutes.

The number of contractions is calculated by multiplying the frequency of the platform by the time of exposure. These contractions are easily tolerated by most patients, no matter their level of function.

As a result of the motion of this platform, the body is safely "thrown" side-to-side at very high speeds over small distances. This movement can occur at a distance of anywhere from 2 mm to 10 mm (amplitude) depending on the foot position one assumes on the platform. It takes place anywhere from 18 to 27 times per second (frequency).

As a result of this forced movement, the body uses its natural stretch reflex to contract the muscles that are required to counter this movement. This is done in an unconscious effort to maintain the body in an upright position and has been hypothesized to involve higher centers of central nervous system modulation.⁵These involuntary contractions are achieved primarily through the fast-twitch fibers of the postural musculature and are believed to occur in up to 90 percent of the involved muscle's fibers. This is a dramatic difference from the 40 to 50 percent thought to be used for most voluntary strengthening exercises-those that comprise a great deal of traditional rehabilitation protocols. These additional contractions occur simultaneously with the larger movements being actively performed on the platform, and therefore serve to enhance the demand on the muscles involved.

With vibration training, the strength of the reflexive muscle contractions is a reflection of the acceleration of the platform. Acceleration, often referred to by manufacturers as the platform's "g-force," is a reflection of the frequency and amplitude of the platform's movement (higher frequencies coupled with higher amplitudes equates to higher g-forces). In contrast to traditional exercise, where we work to increase muscle force output by increasing our mass with weights against a constant acceleration (gravity), vibration training exercises are accomplished by maintaining a constant mass against a changing level of acceleration.

With vibration training, one also achieves increased blood flow,⁶lymphatic system movement, and mechanically induced deformation of restricted connective tissue. These benefits further emphasize that pivotal vibration training is simply one of the most effective forms of functional strengthening that our profession has seen yet. This is supported by the exponentially increasing amount of research being done throughout the world in support of its efficacy; research that has demonstrated its ability to increase muscle power,⁷increase bone density,⁸improve body composition,⁹balance hormone levels¹⁰and improve balance.¹¹

The Future

Up to this point, vibration technology has been nothing more than a curiosity to the western physical therapy world. Its growth has been slow as a result of confusing claims and ambiguous explanations of how exactly it works. For those who have taken the time to explore this technology, questions over the legitimacy of this technology have been raised thanks to cheaply manufactured equipment-equipment incapable of functioning properly and therefore unable to deliver any real value to the patient.

With consideration of proper manufacturing and a review of simple physics, this technology is actually simple to comprehend. With its endless applications, this is a clear example of the impending evolution of exercise science.

Time will soon prove that there's no better means to jump-start a patient's nervous system than vibration training. In accomplishing this otherwise difficult feat, we will be able to more effectively treat patients and maximize progress.

References are available at www.advanceweb.com/pt or by request.

Gabriel Ettenson is a therapist at Equilibrium Physical Therapy LLC, New York, NY.