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

The experiments were conducted in laboratory or simulated settings, not in the patients' actual homes, so real-world environmental factors were not fully captured. The algorithm misses certain functional movements that occur near the vertical position, such as picking an object from the floor or tying shoelaces, because it excludes arm swing during gait. Wrist-worn sensors cannot detect fine finger movements or stabilization tasks that do not involve significant forearm motion. The optimal parameters (15° threshold, ±50° range) were derived from this specific protocol and may not generalize perfectly to other datasets or populations without adjustment. Experiment 1 used only healthy participants, who have larger ranges of motion than stroke survivors, potentially underestimating the errors that might occur in more impaired populations.

The authors declare no competing interests. The study was funded by internal university grants and supported by the EuroMov Digital Health in Motion laboratory.

Do not assume this metric captures all functional arm use. The algorithm specifically excludes movements near the vertical axis to filter out walking arm swing, meaning it will miss tasks like reaching down to the floor or tying shoes. It also does not register fine finger manipulation, so a patient may be using their hand effectively for dexterity tasks while the sensor reports low activity.