External postural perturbations induce multiple anticipatory postural adjustments when subjects cannot pre-select...

Area of Science:

• Human Motor Control
• Biomechanics
• Neuroscience

Background:

• Human balance recovery involves complex postural adjustments.
• Pre-selection of a stepping limb is a potential strategy for effective balance recovery.
• The role of pre-selection in response to unpredictable perturbations remains unclear.

Purpose of the Study:

• To investigate how pre-selecting a stepping limb influences compensatory steps and stability.
• To determine the effects of predictable versus unpredictable stepping leg selection on postural responses.
• To analyze anticipatory postural adjustments (APAs) and center-of-mass (CoM) control during balance recovery.

Main Methods:

• Nine healthy young adults participated in a study involving platform translations.
• Participants experienced predictable (leg known beforehand) and unpredictable (leg selected at onset) conditions.
• Catch trials and voluntary stepping tasks were included to assess response strategies.

Main Results:

• In predictable conditions, subjects made single APAs and stepped accurately.
• Unpredictable conditions led to either multiple APAs with delayed stepping or early stepping with incorrect leg selection.
• Stepping leg pre-selection was observed even in unpredictable scenarios, enhancing stability.

Conclusions:

• Healthy subjects pre-select their stepping limb for balance recovery, even when perturbation details are unpredictable.
• Pre-selection facilitates faster responses and better stability compared to selecting the leg at perturbation onset.
• Relying on visual cues at perturbation onset delays responses and increases instability.