Smartphone-Based Markerless Motion Capture for Spatiotemporal Gait Assessment: Applied Within-Session Reliability and Comparability of OpenCap Versus OptoGait.

Within-device reliability for gait speed, stride length, and cadence was good-to-excellent for both OptoGait and OpenCap across single trials.

• ICC (3,1) values ranged from 0.734 to 0.920 for OptoGait and 0.791 to 0.917 for OpenCap across gait speed, stride length, and cadence.
• Reliability was excellent when averaging three trials: ICC (3,3) = 0.892–0.972 for OptoGait and 0.919–0.971 for OpenCap.
• Study involved 39 healthy adults completing three 10-m overground walking trials at self-selected speed.
• Within-device reliability was assessed using ICC model (3,1) for single measures and ICC (3,3) for averaged measures.

Double support showed lower within-device reliability compared to other spatiotemporal parameters for both devices.

• Single-trial ICC (3,1) for double support was 0.527 for OptoGait and 0.647 for OpenCap.
• These values were notably lower than the good-to-excellent ICC values (0.734–0.920) observed for gait speed, stride length, and cadence.
• Double support was expressed as a percentage of the gait cycle.

OpenCap systematically overestimated gait speed, stride length, and double support compared to OptoGait.

• OpenCap showed higher mean gait speed by +0.110 m/s compared to OptoGait.
• OpenCap showed higher mean stride length by +0.127 m compared to OptoGait.
• OpenCap showed higher mean double support by +3.17% of the gait cycle compared to OptoGait.
• Cadence was very similar between devices, with OpenCap showing only −0.59 steps per minute difference.

Between-device correlations were high for gait speed, stride length, and cadence, but only moderate for double support.

• Pearson correlation between devices was r = 0.951 for gait speed, r = 0.864 for stride length, and r = 0.983 for cadence.
• Correlation for double support was only r = 0.405, indicating moderate agreement.
• Absolute-agreement ICCs were highest for cadence (ICC = 0.980) and lowest for double support (ICC = 0.271).

OpenCap's Advanced Overground Gait Analysis was used to derive spatiotemporal parameters from smartphone-based markerless motion capture.

• OpenCap is a camera-based (CM) system described as a smartphone-based markerless 3D motion capture tool.
• OptoGait, a photoelectric walkway system, served as the comparator and commonly accepted reference device.
• Participants were 39 healthy adults completing three 10-m overground trials at self-selected walking speed.
• The study focused on applied repeatability and practical comparability in scalable clinical and field settings.

The study concluded that OpenCap should be used as a standalone tool rather than interchangeably with OptoGait without device-specific correction.

• Systematic bias between OpenCap and OptoGait across multiple parameters precludes direct interchangeable use.
• Authors recommend using device-specific correction factors or reference values if cross-device comparisons are needed.
• OpenCap was found reliable for within-session monitoring of key spatiotemporal gait measures.
• The findings support OpenCap's potential for scalable clinical and field-based gait assessment as a standalone instrument.