# Validity, reliability, and user perspectives of the newly developed joint angle measurement system: a preliminary study

## TL;DR

A new system for measuring joint angles using sensors and a tablet app was found to be accurate and user-friendly.

## Contribution

A novel joint angle measurement system using six-axis sensors and a tablet app was developed and validated.

## Key findings

- The system showed mean differences and RMSE of less than 0.2° and 1.0° in controlled tests.
- When compared to a goniometer, the system had a mean difference of 0.2° and RMSE of 3.8°.
- User satisfaction scores indicated good usability and satisfaction with the system.

## Abstract

We aimed to evaluate the applicability of a newly developed joint angle measurement system comprising six-axis inertial measurement unit sensors and tablet-based application for estimating joint angles from angular velocity and acceleration data. The application calculated orientation angles from single sensor data, with relative angles calculated using multiple sensors. In experiment 1, validity and reliability were examined using a test device. In experiment 2, static angles of five joints were calculated in four healthy participants using attached sensors and compared with universal goniometer values. In experiment 3, usability and satisfaction were evaluated using the System Usability Scale (SUS) and Quebec User Evaluation of Satisfaction with Assistive Technology (QUEST)-like scale. In experiment 1, mean difference and root mean squared error (RMSE) between the developed system and test device were < 0.2° and < 1.0°, respectively, across all axes. In experiment 2, when data from all joints were pooled, mean difference and RMSE were 0.2° and 3.8°, respectively. Mean difference and RMSE across each joint were < 5°, indicating the system is comparable to universal goniometer. In experiment 3, median SUS and QUEST-like scores were 73.8 and 4.0, respectively, indicating good usability and satisfaction. The developed system has high accuracy and sufficient validity for human joint angles, with good usability and satisfaction.

The online version contains supplementary material available at 10.1038/s41598-025-25640-x.