Predicting dynamic postural instability using center of mass time-to-contact information

Area of Science:

• Biomechanics
• Human postural control

Background:

• Postural stability relies on complex sensorimotor integration.
• Predicting stepping strategies during perturbations is crucial for fall prevention.

Purpose of the Study:

• To determine if spatiotemporal measures of center of mass (CoM) motion relative to the base of support boundary can predict human stepping strategies after upper-body postural perturbations.
• To assess if including CoM acceleration in time-to-contact (TtC) calculations improves prediction accuracy and warning time.

Main Methods:

• Ten young adults received sequential upper-body perturbations via a pendulum, with motion constrained to sagittal-plane ankle rotation.
• Center of mass (CoM) and center of pressure (CoP) velocity and acceleration were measured.
• Boundary-relevant time-to-contact (TtC) measures were compared with traditional postural variables and an inverted pendulum model.

Main Results:

• Peak CoM and CoP velocity and acceleration increased linearly with perturbation severity.
• Boundary-relevant minimum TtC values decreased nonlinearly, predicting stepping responses with quadratic equations.
• Incorporating CoM acceleration into TtC calculations improved prediction accuracy and provided earlier warning of perturbation severity.

Conclusions:

• Spatiotemporal CoM motion relative to the base of support boundary effectively predicts stepping strategies.
• Time-to-contact (TtC) incorporating CoM acceleration may serve as a critical control parameter for transitioning to stepping.
• These findings align with dynamic stability models and offer insights into postural control mechanisms.