Idiosyncratic Characteristics of Postural Sway in Normal and Perturbed Standing

Area of Science:

• Biomechanics
• Human Motor Control
• Neuroscience

Background:

• Postural sway, the body's natural oscillation during quiet standing, is considered idiosyncratic, meaning it is characteristic to each individual.
• Understanding the factors influencing postural sway is crucial for assessing stability and preventing falls, particularly in dynamic environments.

Purpose of the Study:

• To investigate whether individuals with larger physiological sway are more unstable on moving surfaces.
• To determine if postural sway characteristics are consistent within individuals across different conditions.
• To examine the relationship between spontaneous sway velocity and evoked tilt gain during perturbed standing.

Main Methods:

• Nineteen healthy adults stood with eyes closed on a motorized platform that applied subtle sinusoidal disturbances.
• Measurements included spontaneous sway velocity (RMS body angular velocity) and evoked tilt gain (body angle relative to platform tilt).
• Participants experienced quiet standing and standing on a tilting platform (0.1 Hz at 0.2 and 0.4 degrees).

Main Results:

• No significant correlation was found between spontaneous sway velocity and evoked tilt gain (r = 0.34, p = 0.15 and r = 0.30, p = 0.22).
• Spontaneous sway velocity increased with increasing disturbance, and individual sway velocity was consistent across conditions (ICC = 0.95).
• Evoked tilt gain remained consistent within individuals (ICC = 0.79) but decreased as disturbance intensity increased.

Conclusions:

• Postural sway exhibits idiosyncratic characteristics, with individuals consistently displaying their unique sway patterns across different conditions.
• Sway velocity and tilt gain are independent measures, suggesting separate neural control mechanisms for short-term stability and longer-term body orientation.
• These findings highlight the distinct processes involved in maintaining balance under varying sensory and mechanical conditions.