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This paper examines how accurate joint angle measurements must be for effective use in rehabilitation and physical therapy.

March 16, 2026Open Access

Inertial joint angle estimation – How accurate is accurate enough?

Key Points

This paper examines how accurate joint angle measurements must be for effective use in rehabilitation and physical therapy.
Analysis of current clinical practices using visual inspection and goniometers.
Assessment of standard error of measurements (SEM) from isolated tests.
Evaluation of accuracy requirements for automated systems in home use.
Visual estimation shows high variability compared to other methods.
Isolated assessments have SEM values ranging from 1.5° to 6°.
IMU-based systems can be useful without matching goniometer precision for clinical applications.

Abstract

This paper investigates the accuracy requirements for inertial measurement unit (IMU)-based joint angle estimation in rehabilitation and physical therapy. Current clinical practice relies on visual inspection during gait and isolated functional tests using goniometers. While visual estimation has high variability, isolated assessments achieve SEM values between 1.5° and 6°. For home use, automated systems must achieve both low random error and minimal bias to provide objective long-term monitoring. Clinical relevance is determined not solely by measurement precision, but also by minimal clinically important changes. Results indicate that IMU-based systems do not need to match goniometer accuracy to be clinically useful.

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Inertial joint angle estimation – How accurate is accurate enough?

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Abstract

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