Purpose:
Goniometric smartphone applications to measure joint angles offer greater practicality and accessibility, which makes them potential alternatives to a conventional goniometer. The aim of the present study was to evaluate the intra- and inter-examiner reliability in measuring the angles of the range of motion of the knee with the use of the ROM^© goniometric smartphone application.

Method:
The total of 34 young healthy women with an at least 20° limitation in knee extension range of motion participated in the study. Angular measurements of knee flexion in the dominant leg were performed with the aid of the smartphone application by three trained examiners for the evaluation of the inter-examiner reliability. The second evaluation was carried out after a 48-hour period for the determination of the intra-examiner reliability.

Results:
The proposed method demonstrated excellent intra-examiner (intra-class correlation coefficient [ICC] > 0.80) and inter-examiner (ICC > 0.90) reliability, with good intra-examiner (r > 0.85) and strong inter-examiner (r > 0.90) correlations (p < 0.0001), an intra-examiner coefficient of determination (R²) of 0.75, inter-examiner R² of 0.91, and good level of agreement on the Bland-Altman plots for the measures.

Conclusions:
The findings reveal that the ROM^© goniometric smartphone application can be considered a useful tool for the evaluation of the knee range of motion in healthy women.