Postural control in preparation to a step during support surface perturbation.

Area of Science:

• Biomechanics
• Motor Control
• Human Physiology

Background:

• Anticipatory postural adjustments (APAs) are crucial for maintaining stability during voluntary movements like stepping.
• Understanding muscle activation patterns during APAs is key to comprehending balance control.
• Support surface perturbations challenge the neuromuscular system's ability to generate appropriate APAs.

Purpose of the Study:

• To investigate how leg and trunk muscles adjust their anticipatory activity in response to support surface perturbations during stepping.
• To differentiate between reciprocal (R) and co-activation (C) patterns in muscle pairs during APAs.
• To determine which muscle groups (leg vs. trunk) are predominantly modified to ensure stability.

Main Methods:

• Eight healthy subjects performed stepping tasks under normal, forward, and backward support surface perturbation conditions.
• Electromyography recorded muscle activity.
• Reciprocal (R) and co-activation (C) indices were calculated for leg and trunk muscle pairs during APA time intervals.

Main Results:

• Anticipatory muscle activations during support surface perturbation were predominantly characterized by co-activation (C) patterns in leg muscles.
• Significant differences in the maximum displacement of the center of pressure were observed between forward, backward, and normal conditions.
• Leg muscle activation patterns showed greater modification compared to trunk muscle patterns in response to perturbations.

Conclusions:

• Leg muscle activation, particularly co-activation patterns, is significantly modified to ensure equilibrium during stepping with support surface perturbation.
• Trunk muscle activation plays a lesser role in adapting APAs to these specific perturbation types.
• These findings highlight the primary role of the leg musculature in maintaining balance during perturbed stepping.