Development and Validation of an Active Muscle Simplified Finite Element Human Body Model in a Standing Posture

Area of Science:

• Biomechanics
• Human Body Modeling
• Musculoskeletal System

Background:

• Active muscles are crucial for postural stability and influence joint stiffening under dynamic loads.
• Existing full-body finite element models often lack active musculature in standing postures.
• Understanding muscle-induced kinematic responses is vital for injury prevention and performance optimization.

Purpose of the Study:

• To develop and validate the M50-PS+Active model, a simplified human body model with active musculature for standing posture.
• To assess the model's ability to replicate human kinematic responses under gravitational and dynamic loading.
• To enhance the biofidelity of human body models for improved biomechanical simulations.

Main Methods:

• Incorporated 116 skeletal muscles, modeled as 1D beam elements with a Hill-type material model, into the GHBMC M50-PS model.
• Implemented a closed-loop Proportional Integral Derivative (PID) controller for muscle activation strategy.
• Validated the model through gravity standing tests and compared knee kinematics against volunteer data from step-down tests using NASA's ARGOS.

Main Results:

• The M50-PS+Active model effectively maintained a standing posture under gravitational loading, demonstrating active muscle function.
• The model exhibited good biofidelity with volunteer knee kinematics, achieving a CORA score of 0.80.
• The active model significantly improved kinematic prediction compared to the passive M50-PS model (CORA 0.64).

Conclusions:

• The M50-PS+Active model provides a validated tool for simulating human biomechanics in standing postures.
• This model enhances the study of dynamic loading scenarios, including vehicle-pedestrian impacts and space missions.
• The inclusion of active muscles improves the accuracy of lower extremity kinematic predictions in human body models.