Psychometric Properties of a Smartphone Application for Measuring Shoulder Active Range of Motion in Individuals with and without Shoulder Pain and Mobility Deficits

Background: Shoulder pain and mobility deficits impact functional capacity, necessitating the use of reliable tools to assess active range of motion (AROM) for evaluation and monitoring outcomes. This study evaluated the psychometric properties of a smartphone application (PhysioMaster) for measuring shoulder AROM in individuals with and without shoulder pain and mobility deficits. Methods: This cross-sectional study included a cohort of 90 participants, comprising 45 individuals with and 45 without shoulder pain and mobility deficits, recruited through convenience sampling from the Physiotherapy Outpatient Department at Integral University, Lucknow. The participants were aged 20-50 years. Measurements of AROM, including flexion, extension, abduction, external rotation, and internal rotation, were performed using the PhysioMaster application. The readings were compared using a universal goniometer (gold standard). Reliability and criterion validity assessments were conducted by three physical therapists. We calculated the intraclass correlation coefficients (ICC), standard error of measurement (SEM), and minimal detectable change (MDC), and conducted a Bland-Altman analysis to evaluate the agreement between the measurements. Results: The PhysioMaster application demonstrated excellent intra-rater reliability (ICC ≥ 0.944) and good-to-excellent inter-rater reliability (ICC ≥ 0.742) for most movements, although the reliability was slightly reduced for abduction and external rotation in the group without pain, with one isolated measurement showing poor reliability due to sample homogeneity. The criterion validity was high (ICC ≥ 0.944), except for abduction and external rotation in pain-free individuals, which ranged from 0.742 -0.886. Biases were minimal (