Validity of FuncUseRatio for ecological monitoring of functional arm use after stroke: toward precision neurorehabilitation

BACKGROUND: The use of the paretic arm in activities of daily living after stroke is critical to prevent further decline in function over time. Accelerometers offer the opportunity to monitor arm activity during real-life daily activities in home environments. However, commonly used accelerometric metrics may be influenced by passive movements unrelated to functional arm use. In this study, we evaluate the validity of FuncUseRatio for monitoring activities of daily living after stroke. METHODS: Two experiments were conducted. Experiment 1 enrolled 23 healthy participants who performed 22 arm functional movements representative of activities of daily living. Movements of both arms were simultaneously recorded using wrist-worn accelerometers and a Vicon motion capture system allowing a direct comparison between accelerometer-derived forearm orientation and Vicon measurements (gold standard). Experiment 2 included 25 individuals after stroke who performed ecological activities (meal preparation, eating, and dressing). Arm movements were recorded using accelerometers and synchronized video analysis (ground truth), enabling comparison between accelerometer-derived FuncUseRatio and structured video-based arm-use computation. RESULTS: In Experiment 1, forearm orientation estimated from accelerometer data showed excellent consistency with Vicon measurements under dynamic conditions required for FuncUse computation. The intraclass correlation coefficients (ICC) were ICC(C,1) = 0.92 (95% CI 0.82-0.96, p < 0.01) for the right forearm and ICC(C,1) = 0.94 (95% CI 0.86-0.97, p < 0.01) for the left forearm, confirming strong agreement between the two systems. In Experiment 2, FuncUseRatio derived from accelerometer data demonstrated excellent agreement with the structured video-based analysis ratio, considered the ground truth, with (ICC(A,1) = 0.96, 95% CI 0.90-0.98, p < 0.01). CONCLUSION: The FuncUseRatio is a valid measure for assessing functional arm use during activities of daily living in ecologically relevant settings. Its implementation may enable early detection of reduced paretic arm use, including when the patient is at home, facilitate timely reassessment to understand its underlying causes, and thereby allow the implementation of specific arm rehabilitation strategies before any decline in function or participation occurs.