Equilibrium point control cannot be refuted by experimental reconstruction of equilibrium point trajectories

Area of Science:

• * Neuroscience
• * Biomechanics
• * Motor Control

Background:

• * The debate on internal models versus equilibrium point (EP) control for generating arm movements persists in scientific literature.
• * EP control posits that movement is governed by specifying arm configurations where forces balance.
• * Previous research refuted EP control by analyzing kinematic responses to perturbations using mass-spring-damper models.

Purpose of the Study:

• * To evaluate the validity of using mass-spring-damper models to refute EP control.
• * To examine how accurately EP trajectories can be reconstructed from simulated musculoskeletal arm movements.
• * To investigate the influence of musculoskeletal dynamics on estimated model parameters.

Main Methods:

• * Utilized an EP-controlled musculoskeletal arm model for simulations.
• * Simulated unperturbed and perturbed, maximally fast arm movements.
• * Optimized mass-spring-damper model parameters to match simulated kinematic responses.

Main Results:

• * Estimated stiffness was influenced by all dynamical parameters of the musculoskeletal model, not just true stiffness.
• * Reconstructed EP trajectories aligned with literature but differed from the simple trajectories used in simulations.
• * The approach of fitting mass-spring-damper models to kinematic data yielded complex, non-simple EP trajectories.

Conclusions:

• * The refutation of EP control based on mass-spring-damper model analysis is potentially flawed.
• * The method used to reconstruct EP trajectories may not accurately reflect the underlying control strategy.
• * Further research is needed to reconcile findings from different modeling approaches in motor control.