Automatic postural responses are scaled from the association between online feedback and feedforward control.

Area of Science:

• Biomechanics
• Neuroscience
• Human motor control

Background:

• Maintaining upright stability relies on automatic postural responses (APRs) that scale with perturbation magnitude.
• Previous postural perturbation experiences can influence subsequent APRs, suggesting adaptive control mechanisms.

Purpose of the Study:

• To investigate how prior postural perturbations affect the scaling of subsequent automatic postural responses.
• To determine if the sequence of perturbation magnitudes (increasing vs. decreasing) influences APR scaling.

Main Methods:

• Participants experienced unanticipated postural perturbations via cable release, with loads increasing or decreasing (6%, 8%, 10% body mass).
• Center of pressure (COP) displacement and velocity, and gastrocnemius medialis muscle activation onset and rate were measured.
• Postural responses were compared between increasing and decreasing load sequences.

Main Results:

• An increasing load sequence resulted in significantly lower COP displacement and velocity compared to a decreasing sequence.
• The rate of activation for the gastrocnemius medialis muscle was also lower in the increasing load sequence.
• While muscle activation onset latency decreased with increasing load, the load sequence did not significantly affect it.

Conclusions:

• Automatic postural responses to unanticipated perturbations are scaled by integrating current somatosensory feedback with feedforward control derived from prior postural experiences.
• The sequence of perturbation magnitudes influences the adaptive scaling of postural responses, highlighting the role of learning in balance recovery.