IMU-Derived Kinematic Characterization of Drinking Task in Healthy Individuals and Stroke Survivors with Upper Extremity Impairments

Background: Upper extremity (UE) impairment is a common consequence of stroke, restricting daily activities. While assessments such as the Fugl-Meyer Assessment (FMA) and Action Research Arm Test (ARAT) are widely used, their reliance on therapist administration limits frequent home-based evaluations. Inertial measurement units (IMUs) provide a portable, objective method to quantify upper limb kinematics and support scalable tele-rehabilitation, yet evidence on their reliability, validity, and clinical relevance is limited. Objectives: This study aimed to evaluate the test-retest reliability, discriminant validity (vs. healthy controls), and convergent validity (correlation with FMA and ARAT) of eleven IMU-derived kinematic metrics during a standardized drinking task in individuals with subacute stroke. Methods: Fifteen stroke patients and fifteen healthy controls performed the task wearing four IMUs on the upper limb and sternum. Eleven metrics, covering movement time, velocity, smoothness, joint angles, and trunk displacement, were analyzed. Intraclass correlation coefficients (ICCs) assessed reliability, linear mixed models (LMMs) tested discriminant validity, and Pearson's correlations and regression models examined convergent validity. Results: Most metrics showed good to excellent reliability, except for shoulder abduction and maximum elbow angular velocity. All but shoulder abduction demonstrated significant discriminant validity. Movement Time, NMU, SPARC, and LDLJ correlated strongly with ARAT; Movement Time, NMU, and SPARC with FMA. NMU explained 42% of FMA variance, while NMU and SPARC together explained 84% of ARAT variance. Conclusion: IMU-derived metrics from a standardized drinking task provide reliable, valid, and clinically meaningful insights into post-stroke motor recovery, supporting their application in tele-rehabilitation.