Concurrent Validity and Reliability Between Noraxon Ultium™ IMU and Vicon OMC for Lower Limb Gait Assessment Across Variable Walking Speeds.

Background

Wearable inertial measurement units (IMoCAPs) are increasingly used in clinical gait analysis due to their portability and ability to capture data outside laboratory settings; however, validation across operating conditions is essential.

Objective

To evaluate the concurrent validity and reliability of the Noraxon Ultium™ IMU system against a Vicon optical motion capture (OMC) system for lower-limb kinematics during walking across different speeds and time intervals.

Methods

Ten healthy adults performed overground walking at slow, normal, and fast self-selected speeds. Kinematics were recorded simultaneously using both systems. Discrete variables (Max, Min, ROM) were analyzed using three-factor repeated-measures ANOVA (Device × Speed × Time, p < 0.05). Agreement was assessed using Bland-Altman analysis, RMSE, and ICC (3,1), and waveform differences were evaluated using Statistical Parametric Mapping (SPM).

Results

Time effects were minimal across all planes. Sagittal-plane kinematics showed strong agreement, with small biases (<3°), low RMSE (≤2.5°), and moderate reliability (ICC = 0.65-0.74). Both systems detected increased hip and knee motion with speed, although Device × Speed interactions indicated greater IMoCAP underestimation at higher speeds. Frontal-plane agreement was poor to moderate (RMSE: 1-3°, ICC: 0.42-0.74). Transverse-plane kinematics demonstrated the largest discrepancies (RMSE up to 6-7°, ICC: 0.17-0.26), particularly for hip rotation. SPM revealed significant waveform differences across all planes.

Conclusions

The Noraxon Ultium™ IMU provides valid sagittal-plane gait assessment, moderate frontal-plane agreement, and limited reliability for transverse-plane kinematics, requiring cautious interpretation at higher speeds.