An EMG-assisted model of trunk loading during free-dynamic lifting

Area of Science:

• Biomechanics
• Spinal Loading Analysis
• Musculoskeletal Modeling

Background:

• Assessing spinal loading during dynamic lifting is a persistent biomechanical challenge.
• Existing models often lack accuracy for multi-dimensional spinal loads and trunk moments during free-dynamic exertions.

Purpose of the Study:

• To develop and validate a model simulating multi-dimensional spinal loads and trunk moments during dynamic lifting.
• To examine realistic representations of lifting kinetics, kinematics, and trunk mechanics influencing spinal loading.
• To demonstrate the applicability of EMG-assisted modeling for free-dynamic exertions.

Main Methods:

• Developed a biomechanical model integrating measured muscle coactivity (EMG) and external forces.
• Predicted muscle tensile forces using normalized EMG, contractile dynamics, muscle cross-sectional area, and force per unit area.
• Validated the model by comparing measured and predicted trunk extension moments in sagittal and lateral planes.

Main Results:

• Model demonstrated physiological validity with average predicted muscle force per unit cross-sectional area of 50-65 N cm⁻².
• Accurately predicted measured dynamic lifting moments (R² = 0.81 sagittal, R² = 0.76 lateral).
• Compressive and shear spinal loading significantly increased with exertion load, lifting velocity, and trunk asymmetry.

Conclusions:

• The EMG-assisted biomechanical model accurately simulates multi-dimensional spinal loads and trunk moments during dynamic lifting.
• The model provides a valid tool for analyzing free-dynamic lifting exertions and understanding factors influencing spinal loading.
• Findings highlight the impact of exertion load, velocity, and trunk asymmetry on spinal compressive and shear forces.