Reliability and accuracy of a goniometer mobile device application for video measurement of the functional movement...

The squat is a fundamental movement of many athletic and daily activities. Methods to clinically assess the squat maneuver range from simple observation to the use of sophisticated equipment. The purpose of this study was to examine the reliability of Coach's Eye (TechSmith Corp), a 2-dimensional (2D) motion analysis mobile device application (app), for assessing maximal sagittal plane hip, knee, and ankle motion during a functional movement screen deep squat, and to compare range of motion values generated by it to those from a Vicon (Vicon Motion Systems Ltd) 3-dimensional (3D) motion analysis system.

Twenty-six healthy subjects performed three functional movement screen deep squats recorded simultaneously by both the app (on an iPad [Apple Inc]) and the 3D motion analysis system. Joint angle data were calculated with Vicon Nexus software (Vicon Motion Systems Ltd). The app video was analyzed frame by frame to determine, and freeze on the screen, the deepest position of the squat. With a capacitive stylus reference lines were then drawn on the iPad screen to determine joint angles. Procedures were repeated with approximately 48 hours between sessions.

Test-retest intrarater reliability (ICC3,1) for the app at the hip, knee, and ankle was 0.98, 0.98, and 0.79, respectively. Minimum detectable change was hip 6°, knee 6°, and ankle 7°. Hip joint angles measured with the 2D app exceeded measurements obtained with the 3D motion analysis system by approximately 40°. Differences at the knee and ankle were of lower magnitude, with mean differences of 5° and 3°, respectively. Bland-Altman analysis demonstrated a systematic bias in the hip range-of-motion measurement. No such bias was demonstrated at the knee or ankle.

The 2D app demonstrated excellent reliability and appeared to be a responsive means to assess for clinical change, with minimum detectable change values ranging from 6° to 7°. These results also suggest that the 2D app may be used as an alternative to a sophisticated 3D motion analysis system for assessing sagittal plane knee and ankle motion; however, it does not appear to be a comparable alternative for assessing hip motion.

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