Development of Paraplegic Leg Powered Cycling with the Lumbo- Sacral Anterior Root Stimulator Implant

In December 1994 a woman with a complete T9 spinal lesion had a 12-channel stimulator implanted with electrodes on the anterior L2 to S2 spinal roots bilaterally. Some restoration of cycling ability has already been demonstrated in [1] and [2]. She achieved leg powered cycling for 1.2km at a time using a recumbent tricycle in May 1998. The cycling system has since been developed further. Initially, static measurements of pedal forces due to stimulating each implant channel (and also some lumbar and sacral root combinations) were plotted against cycle crank angle. From these tests, stimulation patterns were derived to give the most positive static pedal forces for every crank angle. These stimulation patterns were then used in dynamic cycling tests, the delay between stimulation and muscle response being accounted for by advancing the crank angle for selecting patterns by an angle equivalent to 0.25 seconds at the measured speed. Co-ordinated pedalling was then possible at up to 86rpm. To optimise control program further, we made dynamic pedal force measurements, both on our paraplegic subject and an able-bodied cyclist for comparison. We found that a reduction in simultaneous lumbar and sacral root stimulation improved power output during rapid pedalling.