Abstract
This study investigated the reliability of measuring the trunk rotation range of motion using an additional installed smartphone application (Angle Meter) and its relationship to thoracolumbar flexibility. Trunk rotation is vital for various activities such as swinging bats or rackets and throwing because it influences the movement of the trunk and upper extremities. The participants were 60 healthy male college students, measuring the active range of trunk rotation in a sitting posture using the Angle Meter to measure the angle of left-right rotation. To evaluate reliability, they looked for significant differences, calculated intraclass correlation coefficients, and assessed systematic errors. Additionally, they used the Angle Meter to measure thoracolumbar lateral flexion on both the sides, as well as flexion and extension in the sit and reach test and prone trunk extension test, respectively. The results indicate that there were no significant differences in the repeated measurements of trunk rotation in the sitting position. The intraclass correlation coefficient was impressive at 0.881, indicating high reliability. No additive or proportional errors were found. Thus, the Angle Meter proves to be a useful tool for measuring the active trunk rotation range in the sitting position. However, the trunk rotation range in the sitting position showed a weak correlation with thoracolumbar flexion and no correlation with lateral flexion or extension. In conclusion, the Angle Meter trunk range of motion test is beneficial; however, it has limited relevance to thoracolumbar flexibility.
https://ror.org/00d440w27 
