Anticipatory and Compensatory Postural Adjustments in Response to Dynamic Platform Perturbation during a Forward Step

Area of Science:

• Biomechanics
• Motor Control
• Human Movement Science

Background:

• Maintaining balance during voluntary movements like stepping is crucial.
• Support surface perturbations challenge postural stability and require coordinated muscle responses.
• Anticipatory (APA) and compensatory postural adjustments (CPA) are key mechanisms for balance control.

Purpose of the Study:

• To investigate the generation and interplay of APAs and CPAs during stepping under perturbed conditions.
• To analyze muscle activation patterns in the trunk and shank segments during APA and CPA intervals.
• To understand how these adjustments contribute to balance maintenance and successful stepping.

Main Methods:

• Participants performed stepping tasks with induced support surface perturbations.
• Electromyography (EMG) was used to record muscle activity in trunk and shank segments.
• Analysis focused on co-contraction and reciprocal muscle activation indices during specific time intervals relative to foot-off.

Main Results:

• Trunk muscle co-contraction indices were prominent in the APA intervals (-600 to -400 ms before foot-off).
• Shank muscles showed pronounced reciprocal activation during APA intervals.
• Larger reciprocal muscle activities were observed during CPA intervals compared to APA intervals.
• Subjects modulated both reciprocal and co-contraction patterns to counteract perturbations and facilitate stepping.

Conclusions:

• The study highlights the coordinated use of reciprocal and co-contraction strategies in postural muscles.
• These muscle activation strategies are essential for counteracting external perturbations and ensuring successful stepping.
• Findings advance the understanding of the dynamic interaction between APAs and CPAs in maintaining upright balance.