Modulation of ankle stiffness during postural sway

Area of Science:

• Biomechanics
• Human postural control
• Neuroscience

Background:

• Ankle stiffness is a key component in maintaining upright stance.
• Its contribution to postural control is complex and not fully understood.
• Stiffness is known to be a nonlinear, time-varying system.

Purpose of the Study:

• To investigate how intrinsic and reflex ankle stiffness contribute to postural control.
• To determine the relationship between ankle stiffness and body sway during stance.
• To examine the modulation of intrinsic and reflex stiffnesses during postural adjustments.

Main Methods:

• Subjects stood on an electro-hydraulic actuator, subjected to ankle perturbations.
• Trials included normal, forward lean, and backward lean stances.
• Ankle position, torque, and electromyography (EMG) of leg muscles were recorded.

Main Results:

• Intrinsic and reflex ankle stiffness were significantly modulated by postural sway.
• A complementary relationship was observed: intrinsic stiffness decreased as reflex gain increased.
• This inverse modulation suggests a coordinated strategy for balance control.

Conclusions:

• Ankle stiffness is actively modulated during postural control.
• Intrinsic and reflex stiffness mechanisms interact to optimize balance.
• These findings enhance our understanding of the neuromuscular strategies for maintaining upright stance.