Inertial-sensor-based control of functional electrical stimulation for paraplegic cycling and swimming (2021)

The physical activity and health of people suffering from a spinal cord injury is severely limited due to the accompanying paralysis and often in stark contrast to the physical condition before the injury, especially in young patients. However, participation in sports and therapeutic activities can reduce secondary diseases and improve precisely the overall well-being of those affected. New therapy systems make it possible to produce functional movements by Functional Electrical Stimulation of the paralyzed muscles, thus enabling to perform sports activities. In the first part of this thesis, a novel joint-angle-based stimulation pattern for cycling is presented. Using four inertial sensors attached to the upper and lower legs, knee-joint angles are estimated. The presented stimulation pattern maps the phases of knee-joint angle on the range of 0 to 100 % and activates the muscles for flexion and extension in the corresponding ranges. To reduce the effect of dynamic latency between stimulation onset and muscle response, a correction method was developed that shifts the stimulation pattern by a defined time delay based on the stimulation pattern of the preceding revolution, thus activating the corresponding muscles earlier. The resulting FES cycling system was verified in simulations at different seating positions using a computer model - pedaling could be successfully achieved for all situation using the joint-angle-based stimulation pattern without retuning. Subsequently, the developed algorithms were integrated into the Cybathlon-RehaBike of the Hasomed team. It was shown, that the same setting and stimulation pattern for stationary ergometer cycling can be used for mobile cycling. After 18 months of intensive training, our paraplegic pilot finished fourth in the FES cycling race of the Cybathlon competition with a new personal best time of 6 min 44 s over 750 m. The results show that the joint-angle-based stimulation pattern can be used for smooth and effective FES cycling. Wireless inertial sensors as well as a wearable stimulator are presented as a starting point for the transfer of the methods into cycling systems for home use. The second part of this thesis presents a waterproof electrical stimulation system that enables paraplegics to perform swimming exercises with their own legs for the first time. A ten weeks exploratory study demonstrated that the application with reusable silicone electrodes is safe and can be performed independently by experienced paraplegic swimmers. The study results show that swimming speed is increased by the presented stimulation procedures. In addition, it was shown that by means of an inertial sensor attached to the swimmers back, the roll angle of the trunk can be used to control the stimulation of the knee extensor muscles, allowing a synchronization of the generated leg movement with the voluntary upper body movement during front crawl swimming. This enables a new hybrid form of therapy and rehabilitation for paraplegic patients, which facilitates physical activity with the impaired legs and intact arms.