Validity and Reliability of Sensor-based Measures of Lower Limb Range of Motion in Soccer Players: a Cross-sectional Study.

A deficit in range of motion (ROM) is considered a risk factor for lower extremity injuries in soccer. Analog goniometers are used to measure the ROM of a joint. Sensor-based methods are increasingly being developed, but their quality of testing has not been sufficiently investigated. The purpose of this study was to determine the agreement and the intra- and inter-tester reliability of sensor-based lower extremity ROM measures in soccer players. 36 symptom-free male amateur soccer players (age: 26.3 ± 4.7 years) were included in the study. Three out of five physiotherapists were randomly selected to perform the measurements. Two testers performed the measurements (1. ROM knee from sitting; 2. extension deficit knee from sitting; 3. ROM knee from standing; 4. ROM ankle dorsiflexion [DF] during lunge; 5. ROM ankle plantar flexion [PF] while sitting on a chair) with the digital sensor (index test). The third examiner performed the measurements with the analog goniometer using the neutral-zero method with the subjects in the supine position (reference standard). Pearson's correlation coefficient r, Bland-Altman analysis (BAA), and intraclass correlation coefficient (ICC) were used for statistical analysis (p ≤ 0.05). Only measurements 4 and 5 showed acceptable mean differences of 8.4° (DF) and -10.2° (PF) in the BAA. Measurement 1 showed a moderate correlation (r = 0.582). The sensor-based measurements of knee and ankle ROM revealed excellent intra- and inter-tester reliability (ICC = 0.949-0.986; ICC = 0.895-0.968). However, they showed limited agreement with the established reference standard used here, which can be explained by the different starting positions between the index test and the reference standard.