Related Experiment Video
Updated: Jun 20, 2026
07:51
Video Movement Analysis Using Smartphones (ViMAS): A Pilot Study
Published on: March 14, 2017
Validity of using a smartphone-based markerless motion capture system for quantitative analysis of human dynamic
Huaqing Liang1, Curtis Justin Grant1, Yekaterina Bolgarskaya2
1School of Physical Therapy, Marshall University, Huntington, WV, USA.
Sports Biomechanics
|June 19, 2026
Summary
A new smartphone motion analysis system (OpenCap) shows good accuracy for sagittal plane movements like walking and running compared to traditional motion capture. However, its out-of-plane accuracy is limited, requiring careful consideration for clinical use.
Area of Science:
- Biomechanics
- Human Movement Analysis
- Wearable Technology
Background:
- Traditional 3D motion capture (MoCap) systems are expensive and complex, limiting their use in clinical and sports settings.
- Markerless motion analysis offers a potentially more accessible alternative for quantitative motion assessment.
Purpose of the Study:
- To validate a smartphone-based markerless motion analysis system (OpenCap) against a gold-standard 3D MoCap system.
- To assess the accuracy of OpenCap for lower-extremity joint kinematics across various dynamic tasks.
Main Methods:
- Forty-one participants performed eight dynamic tasks, including walking, running, jumping, and cutting.
- Simultaneous data capture using OpenCap and a 3D MoCap system.
- Kinematic agreement evaluated using discrete metrics (RMSE, NRMSE, Pearson's r, Bland-Altman) and Statistical Parametric Mapping (SPM).
Main Results:
- OpenCap demonstrated strong agreement for sagittal-plane kinematics (e.g., RMSE 7.0°-13.4°, r 0.70-0.99), though it consistently overestimated flexion/dorsiflexion.
- Out-of-plane kinematics showed high normalized errors (NRMSE 29.0%-136.3%) and variable correlations (r -0.09-0.80).
- Performance was better in constrained jumping tasks than expansive translating movements, indicating challenges with rapid translation and distal tracking.
Conclusions:
- OpenCap provides accessible sagittal-plane motion analysis suitable for many clinical and sports applications.
- Current limitations in out-of-plane accuracy restrict its use for precise multi-planar evaluations.
- Users should consider OpenCap's accessibility benefits against its kinematic limitations for specific applications.
