Dimensionality and the dynamics of human unstable equilibrium

Area of Science:

• Biomechanics
• Human Motor Control
• Dynamical Systems Theory

Background:

• Maintaining upright stance requires continuous coordination of multiple joints to control the body's center of mass (COM) over the base of support.
• Understanding the complex interplay between joint movements and COM dynamics is crucial for elucidating balance control mechanisms.

Purpose of the Study:

• To investigate the underlying dynamics of local joint components (foot, hip, head) and global COM in balance control.
• To determine how the availability of sensory information, particularly visual input, influences these dynamics.

Main Methods:

• Dimensional analysis techniques, including the largest Lyapunov exponent and correlation dimension, were employed.
• Participants (N=6) performed a balance task on an unstable platform to assess active degrees of freedom.
• Analysis focused on comparing the dimensionality of local joint movements and COM behavior.

Main Results:

• A similarity in dimensional properties was observed between local joint components and the global COM.
• The behavior of the COM exhibited greater predictability compared to the individual joint components.
• Reduced predictability of local constituents suggests a more integrated control strategy.

Conclusions:

• The dynamics of local joint and global COM components in balance control share similar dimensional characteristics.
• Visual information plays a significant role in stabilizing the low-dimensional dynamics governing postural control.
• The findings suggest that the central nervous system utilizes sensory information to constrain movement variability for effective balance.