A two-muscle, continuum-mechanical forward simulation of the upper limb

Area of Science:

• Biomechanics
• Computational modeling
• Musculoskeletal system analysis

Background:

• Existing musculoskeletal simulations often lack detailed 3D continuum representations.
• Forward-dynamics simulations predict movement from muscle activity, but comprehensive continuum models are limited.

Purpose of the Study:

• To develop and demonstrate a novel 3D continuum-mechanical forward-dynamics simulation framework for musculoskeletal systems.
• To model the upper limb, including bones, muscles, and joint interactions, using continuous volumetric objects.

Main Methods:

• Developed a 3D continuum-mechanical model representing bones and muscles as volumetric objects.
• Modeled muscle-tendon complex behavior as nonlinear hyperelastic material undergoing finite deformations.
• Implemented iterative solutions for position-driven and force-driven scenarios based on minimizing moment equilibrium equations.

Main Results:

• The framework successfully simulated a 3D upper limb model (humerus, ulna, radius, elbow joint, biceps, triceps).
• Predicted realistic moment arms and muscle forces across various activations and motions.
• Quantified contact forces between muscles and bone, showing they can reach 71% of muscle force with minimal impact (<3%) on muscle fiber stretch.

Conclusions:

• The proposed framework enables realistic forward-dynamics simulations of musculoskeletal systems using 3D continuum mechanics.
• Provides novel insights into the influence of contact forces on muscle mechanics.
• Demonstrates the potential for integrating this framework with advanced control algorithms for predicting time-dependent muscle activation.