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These 'Bots Are Made for Walking

Stephen Piazza

Relearning to Walk

Encouraged by those insights, neuroscientists and physical therapists have attempted to adapt the training procedures for spinal animals into therapeutic regimens for patients who have an incomplete spinal cord injury or are recovering from a stroke. Those programs have largely taken the form of body weight-supported treadmill training, in which the patient’s torso is suspended above the treadmill using a harness while two therapists (one for each leg) manually move the legs through the repetitive motions of normal walking.

Treadmill training has been shown to improve strength, stability, and walking ability, but the technique has a significant drawback: It is highly labor-intensive. At least two therapists are needed to move the patient’s legs, and even a single 30-minute training session is fatiguing for the therapists’ arms. Something better was needed. And this time the answer came not from animal studies, but from the world of robotics.

Robotic arms have been common in industrial settings for decades, but recent reductions in the cost and size of sensors, actuators, and computers have led to a proliferation of applications for robots outside of factories. One exciting development is the robotic exoskeleton, a motorized, jointed scaffolding attached around the body to enhance strength and other abilities. Some experimental exoskeletons have been developed with funding from the military to improve a soldier’s ability to carry heavy loads or march over long distances, but exoskeletons have also been designed to assist the disabled, including those undergoing treadmill gait training in rehabilitation.

The most well known and well studied of these rehab devices is the Lokomat, developed by a Swiss team in the 1990s. It looks like a treadmill attached to a small crane, from which the patient is suspended in a harness. The patient’s legs are strapped into an adjustable linkage that has motors and sensors located at the hip and knee joints, as well as passive straps that pull up the patient’s toes to keep them from hitting the treadmill belt when the leg swings forward. The Lokomat exoskeleton’s motors do the work of moving the legs, taking over the job that otherwise would need to be done by human therapists, while the sensors measure the hip and knee joint angles. A computerized controller uses the sensor readings to calculate the forces and torques that the Lokomat applies to the patient’s body.

To assess the effectiveness of robotic rehab training, researchers have compared it with conventional therapy, which involves tasks such as strength and balance exercises, walking between parallel bars, and walking unassisted on a treadmill. Which of those exercises a patient performs depends on the therapist’s judgment of his or her progress. Several groups have looked at stroke patients who are randomly selected for either robotic or conventional therapy, but the results so far are inconclusive. Some studies suggest that walking improves more after robotic training, whereas others suggest the opposite, and still more report no discernible difference between the two approaches.

Other studies have compared the results of robotic gait training with those from treadmill training in which therapists manually move patients’ legs. Here again the results are mixed, but it seems that robotic training offers the greatest benefits to patients early in their rehabilitation programs, when they may not be able to walk at all without the assistance of a robot.

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