The lack of gravity in space reduces the mechanical loading seen by both the muscles and bones of the body, especially those related to standing and moving. The body adapts to reduced loading by losing bone mass and muscle mass. In long-duration space flights this leads to “disuse atrophy,” and an astronaut may lose up to 20% of their bone mass in one year in space. A countermeasure therapy using passive vibration for neuromusculoskeletal stimulation was originally designed by Jeff Leismer, PhD, founder and CTO, VibeTech, Inc., Sheboygan, WI, to enable longer space flights by reducing atrophy.
Down to Earth Need
A similar bone loss and muscle loss occurs on Earth for those with reduced mobility due to injury, surgery, hospitalization, and the aging process. Just as in space, the lack of sufficient loading of the muscles and strains on the bones signals the body to match the capability with the need, leading to muscle and bone loss. The result is that many patients suffering from disuse atrophy do not have the balance or strength to perform weight-bearing physical activity, making conventional physical therapy difficult. Thus, a new therapy modality was developed to mimic biomechanical loading acting on the region of the body most affected by disuse—the lower extremities—without requiring any effort on part of the patient. Studies that have applied similar vibration to standing users have shown that the treatment can help restore both muscle mass and bone density, and further help improve coordination and neural sensation by stimulation of the nerves.
This therapy relies on the alignment of an adjustable compressive force with a precisely controlled vibration along the axis of the tissue to be treated. The compressive force preloads the tissues to be stimulated and allows effective vibration transmission from the foot, through the lower extremities, and into the lower back. This pathway simulates vibrations that are transmitted through the legs due to foot impact with the ground during walking. The force/vibration may be applied and aligned to target different treatment areas with appropriate intensity and frequency profiles needed for the different treatment areas. Standing methods for vibration therapy that use gravity as the force component not only require balance and strength to receive treatment, but also apply the vibration to the “whole body”, which necessarily requires a compromise to protect the more fragile tissues.
Physics and Physiology
The physics behind the treatment involves applying controlled stresses to the bones, resulting in minute tissue deflections (strains). Bone cells detect these controlled strains and direct the body to increase bone density in the portions of the bone experiencing these deflections. For bones with weakened areas, larger deflections will occur in the weakened areas, thus signaling the bone to adapt, and add density right where it is needed. In the case of a healing fracture, this same process again helps direct repair mechanisms at the fracture site, speeding healing. This challenging of the bone to adapt and strengthen is especially important while the bone is still healing and will not support the weight of a patient standing.
The physiology related to improving muscle strength and nerve response with vibration therapy is based on using frequencies and amplitudes that stimulate the body’s stretch reflexes. Correctly applied vibrations engage reflexive muscle contractions, exercising the muscle to reduce atrophy and restore neuromuscular coordination. This process also stimulates nerves that may have been compromised.
The engineering and motion control challenges include the need to provide repeatable and programmable partial bodyweight loading through the lower extremities while generating precise, adjustable vibration dosing targeted at key muscle groups. The vibratory source needs to be programmable, both in amplitude and frequency, to account for the wide spectrum of patients who can be treated by the system. The motion control needs to be consistent over a wide range of partial bodyweight load levels and of patient tissue properties. The stimulation requires the power capability needed to adequately provide stimulation. Finally, the noise level must be kept low for the patient. (See Figure 1)
VibeTech, Inc., has made gravity-independent, effort-free rehabilitative vibration therapy available through its VibeTech One rehabilitation chair. The chair provides reactive loading using a QuickSilver Controls QCI-S2-IG unit that controls a loading mechanism in real-time through closed-loop feedback of applied force. Precisely controlled vibrations are generated by a BEI-Kimco voice coil actuator using a QuickSilver Controls QCI-S3-IG controller and closed-loop feedback from a high-resolution position sensor. The motion of both actuators is directed by the therapist by means of a human-machine interface.
This article was written by Donald P. Labriola, PE, President, QuickSilver Controls, Inc., Covina, CA, and Jeff Leismer, PhD, founder and CTO, VibeTech, Inc., Sheboygan, WI. For information on Quick Silver Controls, Inc., visit http://info.hotims.com/45607-165. For information on VibeTech, Inc., visit http://info.hotims.com/45607-166.