Assessing the Impact of Sensor Orientation on Accelerometer-Derived Angles: A Systematic Analysis and Proposed Error Reduction

Accelerometers have been widely used for motion analysis. The effect of initial sensor orientation (ISO) on the derived range of motion (ROM) is currently unexplored, limiting clarity in understanding error. This two-step study systematically explored the effect of ISO on the error of accelerometer-derived range of motion (ROM) and the effect of a proposed correction algorithm. Accelerometer data were used to compute peak and through-range ROM across a range of ISO and movement angular velocities up to 148 degrees s(-1) compared to an optoelectronic gold-standard. Step 1 demonstrated that error increased linearly with increasing ISO offsets and angular velocity. Average peak ROM RMSE at an ISO of 20 degrees tilt and twist was 5.9 degrees for sagittal motion, and for an ISO of 50 degrees pitch and 20 degrees twist, it was 7.5 degrees for frontal plane ROM. Through-range RMSE demonstrated errors of 7-8 degrees for similar ISOs. Predictive modeling estimated a 3.2 degrees and 3.7 degrees increase in peak and through-range sagittal plane error for every 10 degrees increase in tilt and twist ISO. Step 2 demonstrated error reduction utilizing mathematical correction for ISO, resulting in <1 degrees mean peak error and <1.2 degrees mean through-range ROM error regardless of ISO. Accelerometers can be used to measure cardinal plane joint angles, but initial orientation is a source of error unless corrected.