Machine Restores Mobility to the Partially Paralyzed

It leads until the patient relearns the steps

Photo: VR Lab/University of Tsukuba

23 March 2010—You walk without giving much thought to the complexity of the timing, balance, and muscular force that make it possible. But that complexity becomes all too clear once you’ve sustained injuries to brain or body that destroy muscle memory and make each step a puzzle to solve and a burden to bear.

Researchers at the University of Tsukuba, in Japan, have been working on a system that helps people who have sustained such injuries to walk and even climb stairs. They are presenting a paper detailing their research this week at the 2010 Haptics Symposium, in Waltham, Mass.

The machine was originally created to help address the serious shortage of physical therapists as the Japanese population ages. The machine also has the advantage of never tiring, which means that it can put a patient through his paces repeatedly. The system, called the GaitMaster 5, has the ability to move a patient’s feet either forward—to create a walking stride as long as 70 centimeters—or upward, as high as 31.5 cm, to replicate stair climbing.

It beats a treadmill or a StairMaster, because it doesn’t require the patient to have even basic coordination. The patient’s feet are strapped to sensor-laden pads on motion platforms. (The binding is the same as that used on a snowboard, so the heels and toes are free to move as the feet flex.) As the patient takes his first tentative steps, the system completely controls the movement. The stride, climb, or descent is the exact re-creation of a healthy person’s movement, which has been prerecorded using a motion-capture system. As the patient gains more control, the system can be set to a second training mode that allows more autonomy.

In climbing, for example, one of the platforms rises above the base of the machine and holds still for a moment, bidding the user to ”climb” up on it. That ”stair” begins to move downward in a diagonal trajectory once the pad’s sensors—which can measure 955 pressure points on the sole—detect that the patient has shifted more than one-fourth of his weight to that side. At the same time, the opposite platform swings the other foot upward and forward to repeat the process. Until the patient exhibits enough coordination to shift his weight and maintain his balance, the machine won’t hum along with the mind-numbing sameness that a StairMaster achieves (which is a good thing).

In a series of tests with two stroke victims who were partially paralyzed on one side, the researchers showed that this semivoluntary mode ”has the ability to bring out the patient’s muscle activations on the paralytic side,” says Hiroaki Yano, one of the paper’s coauthors. Once motor function is improved, the roles reverse. The patient uses the machine without the foot bindings, and the system follows the patient’s lead with the aid of foot-position sensors.

It’s rather like teaching a small child to dance by placing her feet on the tops of your shoes—a very human form of engineering.

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