Validity and reliability of the APECS mobile application for assessing knee joint position sense during functional squat tasks in healthy adults

BackgroundKnee joint position sense (JPS) is a vital component of proprioception, significantly impacting functional performance and clinical outcomes.ObjectiveThis study aimed to investigate the concurrent validity and the intra- and inter-tester reliability of APECS-derived JPS error measures during three different squat ranges.MethodsSixty-two participants (mean age: 25.5 ± 3.9 years) were evaluated across three sessions. Knee JPS was measured at low (30-50°), moderate (50-70°), and deep (70-90°) squat ranges. Concurrent validity was evaluated by comparing APECS-derived JPS error measures with digital goniometer-derived measures. Intra-tester reliability was assessed by comparing Sessions 2 and 3 (T1), and inter-tester reliability by comparing T1 and T2 in Session 3. JPS error was quantified using absolute (AAE), relative (RAE), and variable (VAE) angular errors.ResultsCorrelations between APECS- and digital goniometer-derived JPS error measures were low and non-significant across all ranges (r = -0.22 to 0.08). Intra-tester reliability was good only for AAE (ICC = 0.85) and RAE (ICC = 0.79) in the deep squat range, with poor reliability elsewhere. Inter-tester reliability was predominantly poor, with moderate reliability only for VAE in the moderate range (ICC = 0.69).ConclusionUnder the present protocol, APECS-derived JPS error measures showed limited agreement with digital goniometer-derived measures and inconsistent reliability across squat ranges and error parameters. These findings are specific to the present APECS-based assessment protocol and reference method and should not be generalized to the overall validity or reliability of the APECS application.