Concurrent validity and reliability of a mobile iOS application used to assess calf raise test kinematics

Calf raise test (CRT) is used in rehabilitation and sports medicine to evaluate calf muscle function. The Calf Raise application (CR_app) uses computer-vision algorithms to objectively measure CRT outcomes and replicate laboratory-based metrics that are difficult to measure clinically.

To validate the CR_app by examining its concurrent validity and agreement levels against laboratory-based equipment, and its intra- and inter-rater reliability.

Observational cross-sectional validation study.

CRT outcomes (i.e., repetitions, positive work, total height, peak height, fatigue index, and peak power) were assessed in thirteen individuals (6 males, 7 females) on three occasions on both legs using the CR_app, 3D motion capture, and force plate simultaneously. Data were extracted from two markers: below lateral malleolus (n = 77) and on the heel (n = 77). Concurrent validity and agreement were determined from 154 data files using intraclass correlation coefficients (ICC_3,k), typical errors expressed as coefficient of variations (CV), and Bland-Altman plots to assess biases and precision. Reliability was assessed using ICC_3,1 and CV values.

Validity of CR_app outcomes was good to excellent across measures for both markers (mean ICC ≥0.878), precision plots showing good agreement and precision. CV ranged from 0% (repetitions) to 33.3% (fatigue index) and were on average better for the lateral malleolus marker. Inter- and intra-rater reliability were excellent (ICC≥0.949, CV ≤ 5.6%).

CR_app is valid and reliable within and between users for measuring CRT outcomes in healthy adults. CR_app provides a tool to objectivise CRT outcomes in research and practice, aligning with recent advances in mobile technologies and their increased use in healthcare.