Active upper-limb prosthesis for swimming

Abstract

Swimming presents unique challenges for individuals with upper-limb absence, as it requires complex coordination, symmetric propulsion, and control of body balance. Despite these demands, swimming also offers significant rehabilitative benefits, promoting muscle engagement, joint mobility, and cardiovascular health. However, current upper-limb prostheses rarely address the specific requirements of swimming, and most available devices remain passive or non-functional in aquatic environments.

This thesis proposes a novel design for a swimming-specific forearm prosthesis that actively adjusts wrist orientation in response to the swimmer's forearm motion. By segmenting the freestyle stroke into distinct phases—entry, catch, pull, push, and recovery—the control system simplifies the dynamic task into manageable sub-problems. Each phase is associated with a predefined wrist rotation, which simplifies control by reducing the continuous motion into a set of discrete, easily manageable movements. The phase recognition is performed using an inertial measurement unit (IMU), which monitors arm motion and triggers appropriate commands to the servo motor embedded in the prosthesis.

A prototype was developed to demonstrate this concept. The device includes a custom 3D-printed forearm structure that houses all electronic components—IMU, servo motor, controller, and battery—and uses a belt-pulley mechanism to transmit motion. Although the prototype is not yet suitable for use in water, it effectively demonstrates the feasibility of phase-based control for dynamic tasks such as swimming. The design emphasizes modularity, simplicity, and the potential for future development into a fully water-resistant system suitable for rehabilitation, recreational use, or part of training for competitive para-swimmers.