Feasibility of a Markerless Motion Capture System for Estimating Ground Reaction Forces During Vertical Jump and Landing Tasks

Abstract

Background: Vertical ground reaction force is an important kinetic variable for evaluating the biomechanical characteristics of vertical jump and landing tasks and is widely used in performance assessment and injury-risk screening.Aim: To investigate the feasibility of the OpenCap markerless motion capture system for estimating vertical GRF during vertical jump and landing tasks.Material and methods: Eighteen physical education students participated in this study. Kinematic data were collected using OpenCap, and vertical GRF was estimated from whole-body center-of-mass acceleration based on Newton's second law. Estimated GRF was compared with force plate measurements. Phase duration, peak force, mean force, and impulse variables were extracted. Pearson correlation and Bland-Altman analyses were used to assess validity.Results: Strong correlations were observed between OpenCap-estimated and force plate-measured GRF variables. Temporal, impulse, and mean force variables showed moderate-to-very high correlations (r = 0.62–0.94). Bland-Altman analysis indicated biases below 5% for temporal and impulse variables, while biases for propulsive-phase mean and peak force ranged from 5% to 15%. However, peak landing force showed a bias exceeding 40%, indicating substantial underestimation.Conclusions: OpenCap provides a feasible method for estimating vertical GRF during vertical jump and landing tasks and may support large-scale movement assessment. However, peak landing force is substantially underestimated and should be interpreted with caution.