Knee injuries are increasing in the Netherlands, while many physiotherapists are leaving the profession due to high workloads and limited career growth, highlighting a growing gap in rehabilitation services. Through literature research and qualitative interviews, the rehabilitation process, patient challenges, biomechanics, and emotional adaptations after injury were explored. A stakeholder analysis and patient journey mapping revealed that a major barrier to recovery is the misalignment between physical and psychological rehabilitation, known as parallel recovery.
Further research into existing knee wearables and competitor analysis indicated a market gap. While current solutions focus on either physiological or biomechanical measures, few integrate both to address parallel recovery. With the rise of E-health technologies and constrained healthcare access, moving the patient more to home and self management, a system promoting synchronized physical and mental rehabilitation is viable.
Based on these insights, the project scope shifted towards developing a system that enhances parallel recovery using actionable sensor data. Three design directions were developed, with the final concept being Symphysis. Symphysis is a product-service system that detects physiological responses in relation to knee movement through a sensor kit combined with a mobile app and therapist dashboard. It enables patients and physiotherapists to identify emotional challenges during rehabilitation through a unique feedback loop.
The system uses three wearable modules placed on the thigh, shin and wrist , integrating heart rate (PPG), galvanic skin response (GSR), and inertial measurement unit (IMU) sensors. By analysing changes in heart rate variability, skin conductance, range of motion, and movement biomechanics, Symphysis provides insights into how psychological states influence movement patterns. The wearable connects via Bluetooth Low Energy (BLE) to an app that visualizes the data for both patients and therapists, supporting live session tracking, daily monitoring and telerehabilitation.
To test the concept, a functional prototype was developed and evaluated with nine healthy participants. Participants completed three conditions: resting baseline, squats without cognitive load, and squats with a cognitive load (counting backwards in 7s).
Paired sample T-tests showed a significant increase in GSR (P = 0.038, d = 0.83), internal/external rotation range of motion (P = 0.045, d = 0.28), and velocity (P = 0.049, d = 0.17) under cognitive load. Participants also took significantly longer to complete exercises under cognitive load (P = 0.021, d = 0.96), indicating clear effect of the cognitive load, but the differences in time allowed participant use different adaptation strategies, which made comparison more difficult.
These results suggest that Symphysis can detect emotional influences on movement. However, sensor reliability, particularly in the wrist module, needs improvement. Future work should refine the hardware, set a fixed exercise pace to minimize adaptation strategies, and conduct further validation before drawing conclusions and beginning clinical trials.