A stricter condition for standing balance after unexpected perturbations

Area of Science:

• Biomechanics
• Human postural control
• Robotics

Background:

• The extrapolated centre of mass (XcoM) is a key concept for understanding dynamic balance.
• Current balance laws do not account for neural and mechanical delays in Centre of Pressure (CoP) displacement.
• Understanding these delays is crucial for accurate balance assessment.

Purpose of the Study:

• To extend the XcoM theory of standing balance by incorporating the finite reaction and displacement time of the CoP.
• To investigate the effective Base of Support (BoS) under dynamic postural perturbations.
• To analyze human postural control during sudden disturbances.

Main Methods:

• Theoretical extension of the XcoM balance law to include CoP dynamics.
• Experimental study involving human subjects standing on two feet.
• Application of sudden postural perturbations to elicit balance responses.

Main Results:

• The study demonstrates that the effective Base of Support (BoS) is significantly smaller than the static BoS.
• Experimental results show the effective BoS area is approximately 30% of the static BoS area.
• The finite reaction time of the CoP plays a critical role in determining the effective BoS.

Conclusions:

• The refined balance law, accounting for CoP delays, provides a more accurate model of dynamic standing balance.
• The effective BoS is a dynamic entity, reduced by neural and mechanical constraints.
• These findings have implications for understanding human stability and designing more stable robotic systems.