Veterans Affairs

Position-triggered muscle stimulator for wheelchair users

Neuromuscular stimulation applied in response to destabilizing events or when needed for better propulsion

Medical & Biotechnology

Researchers at the Department of Veterans Affairs have devised an electronic device for wheelchair users with spinal cord injuries that stimulates core muscles when integrated motion sensors detect certain movements precipitating a fall. The patent-pending invention is available to companies that would make, use, or sell it commercially.

Patent Illustration

For people with spinal cord injuries who have lost the ability to control their trunk muscles and use a wheelchair, minor disturbances, such as an unexpected turn or bumping a curb can potentially lead to a fall.

Falls are in fact the leading cause of injury for wheelchair users and account for over 66,000 wheelchair related injuries per year. These injuries can be serious and include lacerations, contusions, abrasions, fractures and can result in death. According to at least one survey of people having SCIs, trunk stability is among the top functions they would like to see restored.

Loss of control of trunk muscles also reduces the efficiency of manual propulsion of wheelchairs. Wheelchair users with poor trunk control due to paralysis of core thigh, hip and trunk muscles have limited trunk stability and may be unable to fully lean backward and forward, resulting in inefficient pushing of the wheelchair. The inability to efficiently propel the wheelchair can make traversing challenging terrain, such as inclined ramps, difficult and can also lead to shoulder injuries.

To prevent falls, the researchers built a threshold-based electrical stimulation system that activates the hip and trunk muscles during potentially destabilizing events and during key times in the propulsion arm stroke. The integrated system includes motion sensors for the wheelchair and user’s body position, a computer processor to analyze the input and initiate the electrical signal to electrodes on the person’s body.

The system helps prevent users from falling out of the wheelchair by stimulating selected muscles in response to the motion parameters measured by sensors (inertial measurement unit and accelerometer) and evaluated by algorithms in the software of the controller. When activated, the selected muscles restore trunk stability appropriately in response to the particular destabilizing event.

For better propulsion, the system measures a motion parameter of the user such as anterior-posterior acceleration of a wrist; detects the completed push and recovery, and then applies an electrical stimulation to those trunk muscles (hip flexor muscles, hip extensor muscles, trunk flexor muscles, trunk extensor muscles, abdominal muscles) necessary for a more efficient arm push.  Electrodes can be placed on the surface skin of the user using transcutaneous electrical nerve stimulation equipment or implanted beneath the skin, using intramuscular implants or nerve cuff electrodes.

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