Changes in muscle synergy structure and activation patterns underlie force field adaptation, retention, and...

Area of Science:

• Neuroscience
• Motor Control
• Biomechanics

Background:

• Motor adaptation allows humans to adjust reaching movements to new dynamic environments.
• While kinematic and kinetic aspects are studied, muscle-level coordination during adaptation remains unclear.
• Muscle synergies are proposed as a low-dimensional control mechanism for coordinating muscles.

Purpose of the Study:

• To investigate if changes in muscle synergy structure and activation patterns underlie motor adaptation, retention, and generalization.
• To understand how the central nervous system coordinates muscles during reaching in altered dynamics.

Main Methods:

• 36 male participants practiced reaching movements in a viscous force field.
• Muscle activity from 13 upper-body muscles was simultaneously recorded.
• Retention and generalization to new directions were assessed.

Main Results:

• Adapted reaching required different muscle synergies than unperturbed reaching.
• A novel four-phasic muscle synergy activation pattern emerged with adaptation.
• These structural and activation changes were observed during retention and generalization.

Conclusions:

• Altered dynamics during reaching necessitate structural changes in muscle synergies.
• These modified muscle synergies facilitate motor learning, retention, and generalization.
• Findings offer new insights into the neural control of motor adaptation and coordination.