Concurrent validity and reliability of an iPhone app for the measurement of ankle dorsiflexion and inter-limb asymmetries.

The purpose of this investigation was to analyze the validity and reliability of an iPhone app (named: Dorsiflex) for the measurement of weight-bearing ankle dorsiflexion. To do this, twelve healthy participants (age=28.6±2.3 years) performed a weight-bearing lunge test with each leg in five separate occasions, while dorsiflexion angle was simultaneously registered using a professional digital inclinometer and the Dorsiflex iPhone app, which was specifically developed for this study. A total of 120 angles measured both with the digital inclinometer and the app were then compared for validity, reliability and accuracy purposes using several statistical tests. There was an almost perfect correlation between the digital inclinometer and the Dorsiflex app for the measurement of ankle dorsiflexion (r=0.989, 95% CI=0.986-0.993, SEE=0.48º), with trivial, non-significant differences between devices (SMD=0.17, p=0.10). When analyzing the reliability of the app for the measurement of five different trials for each participant, similar coefficients of variation (CV) were observed in comparison with those obtained with the digital inclinometer (Dorsiflex app: CV=5.1±2.3 %; Digital inclinometer: CV=4.9±2.5 %). The results of the present study show that weight-bearing ankle dorsiflexion can be easily, accurately, and reliably evaluated using the Dorsiflex iPhone app.