Holding Static Arm Configurations With Functional Electrical Stimulation: A Case Study

Functional electrical stimulation (FES) is a promising solution for restoring functional motion to individuals with paralysis, but the potential for achieving any desired full-arm reaching motion has not been realized. We present a combined feedforward-feedback controller capable of automatically calculating and applying the necessary muscle stimulations to hold the wrist of an individual with high tetraplegia in a desired static position. We used the controller to hold a complete arm configuration to maintain a series of static wrist positions. The average distance to the target wrist position, or accuracy, was 2.9 cm. The precision is defined as the radius of the 95% confidence ellipsoid for the final positions of a set of trials with the same muscle stimulations and starting position. The average precision was 3.7 cm. The control architecture used in this study to hold static positions has the potential to control arbitrary reaching motions.