Related Experiment Videos
Variation in spinal load and trunk dynamics during repeated lifting exertions
K P Granata1, W S Marras, K G Davis
1Motion Analysis and Motor Performance Laboratory, University of Virginia, 2270 Ivy Rd, Charlottesville 22903, USA.
Clinical Biomechanics (Bristol, Avon)
|October 16, 1999
Summary
Repeated lifting causes significant spinal load variability, even with identical tasks. Experienced workers show greater spinal loads and variability, highlighting risks beyond average measurements.
Area of Science:
- Occupational biomechanics
- Ergonomics
- Spinal loading analysis
Background:
- Traditional biomechanical models underestimate spinal load variability in repeated lifting.
- Existing models overlook variations in lifting dynamics and muscle coactivity.
Purpose of the Study:
- Quantify variability in lifting motions, trunk moments, and spinal loads during repeated exertions.
- Identify workplace factors influencing biomechanical variability in manual material handlers.
Main Methods:
- EMG-assisted model of spinal loading using trunk dynamics, moments, and muscle activities.
- Manual material handlers (5 experienced, 7 inexperienced) performed repeated lifts under varying load weights, task asymmetry, and lifting velocities.
Main Results:
- Box weight, task asymmetry, and experience significantly influenced spinal load magnitude and variability.
- Experienced subjects exhibited greater spinal loads and within-subject variability than inexperienced subjects.
- Trial-to-trial variability contributed to 14% of compression and 32% of lateral shear load variation; over 20% of lifts exceeded NIOSH limits due to variability.
Conclusions:
- Spinal load fluctuates significantly between individual lifting exertions, even with consistent task parameters.
- Trial-to-trial variability in kinematics, kinetics, and spinal load are influenced by workplace factors and may contribute to low-back pain risk.
- Ergonomic assessments must consider spinal load variability, not just mean values, as a substantial portion of lifts can exceed safety limits.