Central programming of postural movements: adaptation to altered support-surface configurations.

Area of Science:

• Neuroscience
• Biomechanics
• Motor Control

Background:

• Maintaining balance during postural perturbations is crucial for human stability.
• Automatic postural adjustments are essential for preventing falls.
• Understanding the underlying motor programs can reveal principles of human movement control.

Purpose of the Study:

• To investigate if automatic postural actions are organized by a limited set of central motor programs.
• To determine if muscle activation patterns differ based on support surface length.
• To assess the influence of prior experience on postural movement strategies.

Main Methods:

• Subjects stood on support surfaces of varying lengths.
• Horizontal surface perturbations (forward/backward) were applied.
• Muscle activation patterns (latency, sequence) and resulting body movements were analyzed.
• Postural strategies (ankle vs. hip) were identified based on muscle activity and joint torques/forces.

Main Results:

• Ankle strategy: stereotyped muscle activation (ankle to trunk) with delayed latency (73-110 ms), generating ankle torque.
• Hip strategy: different muscle activation sequence (trunk/thigh), minimal ankle response, generating horizontal shear force.
• Intermediate surfaces elicited combined ankle and hip strategies.
• Initial practice trials showed complex patterns resembling intermediate strategies, with unchanged latencies.

Conclusions:

• Automatic postural control relies on a limited repertoire of muscle activation patterns (ankle and hip strategies).
• These strategies are flexibly combined and adapted based on environmental constraints (support surface length).
• Prior experience influences the selection and execution of postural control strategies.