An Inertial Sensor-based Trigger Algorithm for Functional Electrical Stimulation-Assisted Swimming in Paraplegics

Functional electrical stimulation (FES) is used to support gait in stroke patients and to induce cycling motions in paralyzed legs. In the current contribution, we present a method that, for the first time, enables FES-supported swimming in paraplegics. The proposed setup includes a waterproof stimulator, cables, and electrodes. In preliminary experiments, flexion and extension movements of the knee were generated in a completely paralyzed subject to support the propulsion. Furthermore, transcutaneous spinal cord stimulation (tSCS) is used to get a straight swimming position and to reduce spasticity of the lower extremities. The developed setting remained dry and safe during all sessions. The first trials revealed the need for a synchronization of the patient's arm movements with the artificially induced leg movements to prevent undesired rolling movements of the swimmer. To enable such a synchronized swimming, a trigger algorithm was developed that is based on the roll angle and angular velocity of the trunk. By experimental validation, it was demonstrated that a functional stimulation pattern can be generated during front crawl movements of the upper body. The new setup and methods are currently being tested during the STIMSWIM pilot study with paraplegics. The preliminary results of the first two subjects show an improvement of the swimming speed of approximately 15% for FES/tSCS assisted swimming compared to non-assisted swimming and a clear training effect over the first 7 sessions.