Validity and Reliability of Smartwatch-Based Upper-Extremity Function and Heart Rate Assessment in Outpatients Older Adults

BACKGROUND: We previously developed and validated a 20-second upper extremity function (UEF) test for frailty assessment using wearable-derived motor and heart rate (HR) metrics. OBJECTIVES: To evaluate, among older adults in hospital, the validity of a smartwatch for extracting UEF motor and HR outcomes relative to wearable sensors, and the test-retest reliability of UEF motor and HR outcomes across two back-to-back trials. METHODS: Adults ≥65 years performed the UEF task. Motor outcomes included elbow angular speed, moment, range of motion, speed reduction, and speed variability. HR outcomes included mean HR during baseline, task, and post-task, and measures of HR increase and recovery. In Experiment I (validation), motor outcomes were compared between motion sensor and smartwatch (n = 43; age=68.98 ± 13.3), and HR outcomes between ECG sensor and smartwatch (n = 23; age=77.26 ± 8.62). In Experiment II, test-retest reliability was quantified for motor outcomes (n = 133; age=73.04 ± 10.99) and HR outcomes (n = 85; age=74.53 ± 9.83). Agreement and repeatability were quantified using two-way mixed effects intraclass correlation coefficients (ICC). RESULTS: Smartwatch demonstrated moderate-to-excellent agreement with the motion sensor (ICC = 0.67-0.90) and good-to-excellent agreement for most (78%) HR features (ICC = 0.75-0.94). Test-retest reliability within repeated trials was good-to-excellent for most (83%) motor outcomes (ICC = 0.75-0.96), and for most (78%) HR outcomes (ICC = 0.80-0.96). CONCLUSIONS: A brief seated UEF assessment provides reproducible motor and HR-derived measures in clinic. Further a smartwatch may capture UEF motor outcomes and most HR features with agreement relative to reference sensors.