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OpenCap
Capture clinical-grade musculoskeletal forces and 3D kinematics using just two smartphones for researchers and clinicians to track movement without a lab.
About OpenCap
OpenCap is an open-source platform developed at Stanford University that enables high-fidelity motion capture and musculoskeletal modeling using only two iOS devices. By leveraging computer vision and machine learning, it transforms standard smartphone video into 3D kinematic and kinetic data, traditionally only available in expensive, specialized motion capture laboratories. The tool is designed to democratize access to biomechanical analysis, making it possible to study human movement in real-world settings like clinics, gyms, or sports fields. The system works by synchronizing video from two iPhones or iPads and processing the footage through a cloud-based pipeline. It uses advanced AI to track body markers and then applies musculoskeletal simulations to estimate joint angles and the internal forces acting on muscles and bones. Users can visualize these results directly in a web browser, comparing different sessions or exporting the data for further research. The workflow includes a guided setup process to ensure camera calibration and subject scaling are accurate for scientific use. This tool is primarily intended for researchers in biomechanics, physical therapists, and sports scientists who need objective movement data but lack the budget or space for optical motion capture systems. It is particularly useful for longitudinal studies in rehabilitation or performance tracking in athletics where natural environment data is more valuable than lab-constrained movements. Because it provides clinical-grade metrics, it bridges the gap between wearable sensors and high-end lab equipment. What distinguishes OpenCap from other mobile pose estimation tools is its integration with OpenSim, a standard musculoskeletal modeling software. Instead of just providing 2D or basic 3D stick figure coordinates, it calculates actual physical forces and moments. Its development by Stanford’s Neuromuscular Biomechanics Laboratory ensures a level of scientific validation that many commercial AI-pose apps lack. Note that it currently requires iOS devices and a web-based setup, focusing on scientific accuracy over casual consumer use.
OpenCap pros & cons
Pros
- Provides clinical-grade musculoskeletal forces and kinematics without expensive lab hardware.
- Leverages standard iOS devices, making it highly portable for field-based research.
- Integrates directly with OpenSim for advanced biomechanical simulation and analysis.
- Developed and validated by Stanford University’s Neuromuscular Biomechanics Laboratory.
- Supports collaborative research through shared session data and a dedicated forum.
Cons
- Does not support Android devices, requiring specific Apple hardware for recording.
- Requires a stable internet connection for cloud-based video processing and analysis.
- Workflow involves a multi-step calibration process that may be complex for casual users.
- Limited to specific camera setups for the current web application implementation.
OpenCap use cases
- Physical therapists can track patient recovery by analyzing 3D joint loads during rehab exercises in a standard clinic setting.
- Sports scientists can evaluate athlete form on the field to identify injury risks or optimize performance using mobile devices.
- Biomechanics researchers can conduct large-scale longitudinal studies outside of the lab to gather real-world movement data.
- Clinical researchers can use the tool to obtain objective gait analysis data without the high cost of traditional motion capture.
OpenCap features
- cloud-based video processing
- multi-camera synchronization
- clinical-grade data export
- web-based data visualization
- opensim integration
- 3d kinematic analysis
- musculoskeletal force estimation
- smartphone-based motion capture
OpenCap pricing
Is OpenCap free? Yes, OpenCap has a free plan.
Open Access
Free
- iOS recording app
- 3D kinematic results
- Musculoskeletal force modeling
- Cloud data processing
- OpenSim file export
- Community forum access
OpenCap FAQs
Which mobile devices are compatible with OpenCap?
OpenCap currently supports iOS devices, such as iPhones and iPads, for video recording. The development team has explicitly stated that Android devices are not supported at this time.
Do I need a verification code to install the app?
No, there is no need for a verification code when installing the iOS web app. Users simply need to visit the Get Started page on the official website and follow the two-step installation process.
How does OpenCap calculate musculoskeletal forces?
The tool uses computer vision to track body movement from multiple smartphone angles and then processes that data through cloud-based musculoskeletal models to estimate internal joint and muscle forces.
Where can I find help if I encounter technical issues?
Technical questions should be directed to the OpenCap forum on SimTK. Users are encouraged to consult the FAQ and troubleshooting documentation before posting new queries.
Ratings & reviews
No reviews yet. Be the first to share how OpenCap worked for you.
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