Concurrent validity of markerless motion capture for occupational lifting: Kinematics and ergonomic risk assessment.
Markerless motion capture systems can be useful for ergonomic assessments in symmetrical lifting but may be less reliable for complex tasks.
Where it sits
this study against the rest of the slu-pp-332 (exercise mimetic) corpusSummary and findings
This study evaluated the validity of markerless motion capture systems for assessing ergonomic risk during lifting tasks in healthy participants. Two systems, OpenCap and MediaPipe, were compared against a marker-based reference system (Vicon) using the Rapid Entire Body Assessment (REBA) tool. The findings indicated increased error rates in more complex lifting tasks.
Abstract
Markerless motion capture has the potential to enhance ergonomic risk assessment, but evidence remains limited for occupational manual handling tasks of increasing complexity. This study compared a multi-view system (OpenCap) and a monocular system (MediaPipe) against a marker-based reference system (Vicon) for lifting kinematics. Outcomes were assessed using the Rapid Entire Body Assessment (REBA) risk assessment tool. Twenty healthy participants performed three two-handed lifting tasks of increasing complexity under controlled laboratory conditions. Errors increased by 15-30% from symmetrical to asymmetric multi-planar tasks, with both systems demonstrating lower error in the sagittal plane (RMSE = 9.9-31.2°) than in the frontal and transverse planes. Both systems were reliable for symmetrical lifting, including high REBA agreement, but validity declined for tasks involving trunk rotation and walking. MediaPipe showed lower error for trunk and proximal joints, whereas OpenCap performed better for distal kinematics, informing practical system selection.
Background
This paper addresses the need for improved ergonomic risk assessment tools in occupational lifting tasks. Existing methods, particularly marker-based systems, have limitations in terms of practicality and flexibility. The study evaluates the performance of markerless motion capture systems, which could potentially streamline ergonomic assessments in complex lifting scenarios.
Methods
The study employed a controlled laboratory design with twenty healthy participants performing three two-handed lifting tasks of increasing complexity. The primary outcome measure was the comparison of lifting kinematics between a multi-view system (OpenCap), a monocular system (MediaPipe), and a marker-based reference system (Vicon). The Rapid Entire Body Assessment (REBA) tool was used for risk assessment.
Results
Errors increased by 15-30% from symmetrical to asymmetric multi-planar tasks. The RMSE for both systems in the sagittal plane ranged from 9.9 to 31.2°. Both markerless systems showed high agreement with REBA for symmetrical lifting, but validity decreased for tasks involving trunk rotation and walking.
Interpretation
The findings suggest that while markerless systems can be reliable for symmetrical lifting tasks, their validity diminishes with increased task complexity. The effect sizes reported, such as the 15-30% increase in errors, may be statistically significant but could be considered clinically small in the context of ergonomic assessments. Limitations include the small sample size and the controlled laboratory setting, which may not fully replicate real-world conditions.
Key findings
- Errors increased by 15-30% from symmetrical to asymmetric multi-planar tasks.
- RMSE = 9.9-31.2° for both systems in the sagittal plane.
- Both systems demonstrated high REBA agreement for symmetrical lifting tasks.
- Validity declined for tasks involving trunk rotation and walking.
- MediaPipe showed lower error for trunk and proximal joints.
- OpenCap performed better for distal kinematics.
Limitations
- small n=20 participants
- controlled laboratory conditions may not reflect real-world scenarios
- validity declined for tasks involving trunk rotation and walking
- not all error metrics reported