Development of a novel MATLAB-based framework for implementing mechanical joint stability constraints within OpenSim...

Area of Science:

• Biomechanics
• Computational Biology
• Human Movement Science

Background:

• Static Optimization (SO) in OpenSim estimates muscle forces and activations to balance applied moments.
• SO alone may not fully capture complex muscle behaviors, especially those requiring joint stability.
• Enhanced models are needed for more accurate biofidelic simulations.

Purpose of the Study:

• To introduce and validate Stability-Constrained Static Optimization (SCSO) as an enhancement to OpenSim's SO solver.
• To assess if SCSO produces more biofidelic muscle activations compared to SO, particularly in scenarios requiring co-contraction for stability.
• To test SCSO's efficacy using existing biomechanical models and experimental electromyography (EMG) data.

Main Methods:

• Developed an open-access MATLAB interface to enhance the SO solver with mechanical stability constraints, creating SCSO.
• Applied both SO and SCSO to a spine model for two simulations involving different postures and external load heights.
• Compared predicted muscle activations from SO and SCSO against literature-based experimental EMG data.

Main Results:

• SCSO demonstrated reduced average deviation from EMG data (6.8%–7.5%) compared to SO (10.2%) in simulation 1.
• In simulation 2, SCSO predicted increases in back and abdominal muscle activations with higher loads, aligning better with experimental data than SO's constant predictions.
• SCSO results showed greater biofidelity, reflecting the central nervous system's strategies in muscle force distribution and antagonistic muscle activation.

Conclusions:

• SCSO provides a more biofidelic estimation of muscle activations and forces than standard SO by including mechanical stability requirements.
• The SCSO approach is applicable to various OpenSim models and enhances biomechanical simulations, especially when joint stabilization is critical.
• While SCSO's sensitivity to parameters like musculotendon stiffness requires consideration, it offers a significant advancement for realistic human movement modeling.