Body-Weight Supported Treadmill Training is a practical physiologically based experimental method for promoting ambulation, now being tested in patients with stroke and spinal cord injury. It grew out of a century's or more of work in the basic physiology of the spinal cord, looking at pattern generators therein.
The Central Pattern Generator
The central pattern generator (CPG) is a functional construct; not like a circuit board that is hardwired, but more like a software program imposed on the central nervous system. These circuits can work, and they can work relatively independently. However, one of the key questions is how independently can they work? CPG's may be involved with a number of motor activities in different kinds of animals, but to what degree, depending on brain control, is a quite interesting and, as yet, unsolved question.
There has been a long debate as to whether the CPG is present in humans, and, if present, what might be the minimum requirement to activate it. The evidence for the human CPG is largely anecdotal, and includes reports of spontaneous rhythmic movements occurring in paralyzed individuals in the absence of external limb manipulation.
Recently, a published report from Miami described a paralyzed patient's hip infection apparently causing patterned lower limb movements to occur. When the infection resolved, the patterned movement stopped. Another recent publication reports that tonic spinal cord stimulation caused rhythmic lower extremity movements. Finally, and most importantly, we have had the actual experience of using body weight support as a method of ambulation training.
Body Weight Supported Treadmill Training—Background
This method is the same as has been used in the spinally injured cat. The front of the animal was suspended in a containing apparatus over a treadmill and the rear weight is supported via the tail; the rear (paralyzed) legs were observed walking when the treadmill moved.
A human in a weight-supporting harness can show some of the same function.
Dr. Anton Wernig from Bonn, has probably the largest published experience in body weight supported treadmill training for spinal cord injury. He has shown that this process is not something you have to do during the acute phase; but rather a therapy that can be implemented at any point post injury. Indeed, if you want to demonstrate that the method is better than current therapies, chronic cases are more suitable. Just about everybody improves to some extent after a fresh injury, but lack of improvement practically defines the chronic state. Wernig has found that most chronic patients can be improved.
We have conducted a small feasibility study of nonfunctional ambulating subjects, all more than 1 year post injury (one was about 12 years), trained for 12 weeks, 5 days a week, 20 to 30 minutes a day. Initially about 40 percent of their body weight was supported, and then the support was adjusted to the individual tolerance. The subjects progressed to over-ground walking using body weight support. We tested them at baseline and at 1-month intervals. Primary outcomes were walking speed, a 5-meter timed walk without support; walking endurance, a 5-minute timed walk; and the metabolic cost of walking. (This last is a very important parameter to make sure that the ambulation is energy efficient.)
Every measure that we used appears to improve significantly, and motor control patterns changed.
We are conducting follow-up studies at present, as we are interested in establishing how well the patients maintain these gains. It is necessary for everyone to practice in order to maintain acquired skills. So far we have observed that ambulation distances can continue to increase, with the most dramatic change in ability increasing from 30 to 800 meters walking distance. Oxygen consumption may be the most interesting parameter measured; it went up at first and then back down. These are all free over-ground measures. They were not done with support, but with whatever assistance the patients needed to do it. For instance, subjects may have used a walker. The EMG patterns from an aligned protocol on transference of learning indicated that when you improve control in one modality, very likely you will see a transfer into another. We have seen this in other cases, but in the speed of moving alone you can see it much faster. The subjects are able to do it much more quickly and more efficiently after the unloaded training.
Body Weight Supported Treadmill Training—The Mechanics
Therapists elicit the reflex activity by tactile stimulation and guiding the limb. They are constantly instructing the patient: "positioning," "transfer your weight," and so on. It is a very intensive for the therapist and the patient. Both are sweating profusely after 20 minutes of walking. The approach is labor intensive, and so you have to convince people that it is worth all the effort.
Another issue is providing an effective harness that will hold the proper amount of body weight in the proper posture. It is also necessary to use a treadmill with the proper speed. Most treadmills in most PT areas do not go less than half a mile per hour and the appropriate speed for this sort of training is about one-tenth of a mile per hour.
Multiple Sclerosis
Regardless of whether the results we see are due to the CPG or not, body weight supported treadmill training appears to be an effective way to train people to get moving again. But what are the implications for MS? This process makes possible ambulation therapy for those who are too weak to manage conventional therapy and you can do a more effective job in training at a task the patient really wants to achieve. You can actually get people in upright posture, elicit posture reflexes and so on. A potential risk for the MS population is over exertion. Therefore, this is a therapy for which population specific systematic trials are necessary.
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