Comparison of Kinematics and Kinetics Between OpenCap and a Marker-Based Motion Capture System in Cycling

TL;DR

This study compares marker-based and markerless OpenCap motion capture systems during cycling, assessing their agreement in measuring joint kinematics and kinetics, and finds high correlation for key joint angles.

Contribution

It provides the first detailed comparison of OpenCap and marker-based systems in cycling, demonstrating OpenCap's accuracy in joint angle assessment.

Findings

High correlation (r > 0.9) for hip, knee, and ankle joint angles.

OpenCap shows strong agreement with marker-based systems in cycling.

Results support OpenCap's use for natural movement analysis in real-world settings.

Abstract

This study evaluates the agreement of marker-based and markerless (OpenCap) motion capture systems in assessing joint kinematics and kinetics during cycling. Markerless systems, such as OpenCap, offer the advantage of capturing natural movements without physical markers, making them more practical for real-world applications. However, the agreement of OpenCap with a marker-based system, particularly in cycling, remains underexplored. Ten participants cycled at varying speeds and resistances while motion data were recorded using both systems. Key metrics, including joint angles, moments, and joint reaction loads, were computed using OpenSim and compared using root mean squared error (RMSE) per trial across participants, Pearson correlation coefficients (r) per trial across participants and repeated measures Bland-Altman to control trials dependency within subject. Results revealed very strong agreement (r GT 0.9) for hip (flexion/extension), knee (flexion/extension), and ankle (dorsiflexion/plantarflexion) joint angles.