Postural feedback responses scale with biomechanical constraints in human standing

Area of Science:

• Biomechanics
• Neuroscience
• Human Motor Control

Background:

• Human postural responses are crucial for maintaining balance against external disturbances.
• Previous models suggested fixed feedback gains, but biomechanical limits necessitate adaptable control.
• Understanding how the central nervous system scales postural control is key to explaining adaptive responses.

Purpose of the Study:

• To determine if human postural responses can be modeled using feedback control gains.
• To investigate if these gains are scaled by the central nervous system to accommodate biomechanical constraints.
• To analyze the relationship between perturbation magnitude and postural control adjustments.

Main Methods:

• Applied controlled backward perturbations of varying magnitudes (3-15 cm) to healthy volunteers.
• Utilized a 3-segment, sagittal-plane biomechanical model and a linear state feedback controller.
• Employed optimization techniques to identify best-fit feedback control gains for each perturbation trial.

Main Results:

• Postural response trajectories (joint angles and torques) scaled proportionally with perturbation magnitude.
• Feedback control gains provided a good fit to the experimental data (R²=0.92).
• Gains were multivariate and heterogeneous; joint torques depended on multiple joint movements.
• Hip gains increased and ankle gains decreased linearly with perturbation magnitude, reflecting biomechanical limits.

Conclusions:

• Human postural adjustments can be effectively described by a unified feedback control scheme.
• The central nervous system employs scalable, heterogeneous feedback gains that adapt to biomechanical constraints.
• This adaptive gain scaling allows for robust postural control across a range of perturbation intensities.