Reliability and Validity of IMU-Derived Kinematic Metrics of a Drinking Task in Stroke Survivors and Healthy Individuals

Abstract

Upper extremity (UE) impairment is a common consequence of stroke, restricting daily activities. Clinical assessments such as the Fugl–Meyer Assessment (FMA) and the Action Research Arm Test (ARAT) are widely used but are typically therapist-administered. Inertial measurement units (IMUs) provide a portable, objective method to quantify upper limb kinematics and may therefore support scalable tele-rehabilitation. Yet, evidence on their reliability, validity, and clinical relevance remains limited. This study evaluated 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. Fifteen stroke patients and fifteen healthy controls performed the task wearing four IMUs on the upper limb and sternum. Both joint and end-point kinematics were derived using the Madgwick sensor fusion algorithm. Reliability was assessed through intraclass correlation coefficients (ICCs), discriminant validity through linear mixed models (LMMs), and convergent validity through Pearson’s correlations and regression models. Most metrics showed good to excellent reliability (ICC≥0.75), except for shoulder abduction (ICC=0.18) and maximum elbow angular velocity (ICC=0.65). All but shoulder abduction demonstrated significant discriminant validity. Movement time and measures of smoothness correlated moderately to strongly (r≥.67) with ARAT and FMA. These findings indicate that IMU-derived metrics during a standardized drinking task provide reliable, valid, and clinically meaningful insights into post-stroke motor status, and may offer supplementary information for movement assessment beyond conventional clinical scales.