Muscle coactivation: definitions, mechanisms, and functions.

Area of Science:

• Neuroscience
• Biomechanics
• Motor Control

Background:

• Muscle coactivation, the simultaneous contraction of agonist and antagonist muscles, influences movement mechanics.
• Existing research highlights its role in joint stiffness, movement speed, and action stability.
• The neurophysiological underpinnings and implications for motor control strategies require further elucidation.

Purpose of the Study:

• To explore the consequences of agonist-antagonist muscle coactivation on movement mechanics and stability.
• To investigate the role of coactivation within established motor control theories, such as the equilibrium-point hypothesis.
• To propose a neural control strategy hypothesis explaining the functional significance of muscle coactivation.

Main Methods:

• Conceptual analysis and theoretical integration of existing research on muscle coactivation.
• Discussion within the framework of hierarchical control and spatial referent coordinates.
• Illustration of coactivation's relation to changes in neural commands (e.g., c-command).

Main Results:

• Coactivation impacts movement mechanics by increasing joint stiffness and potentially facilitating faster movements.
• The effect of coactivation on movement stability is context-dependent, varying with the kinematic chain's origin.
• A hypothesis is proposed where coactivation serves as a deliberate neural strategy for preserving effector-level control.

Conclusions:

• Agonist-antagonist coactivation is a strategic neural mechanism for stabilizing motor actions through coordinated adjustments.
• This strategy prevents the need for controlling individual muscle signals, simplifying motor control.
• The hypothesis accounts for increased coactivation in challenging tasks and in populations with motor impairments.