Slow dynamics of human balance control

Area of Science:

• Biomechanics
• Human motor control
• Sensory integration

Background:

• Human sway behavior at low frequencies (<0.1 Hz) suggests a slow feedback component in balance control.
• This may involve a self-calibration mechanism referencing kinematic and force sensory cues.
• Previous studies were limited by short trial durations and small sample sizes.

Purpose of the Study:

• To investigate the properties of the mechanism reducing body sway at very low frequencies during upright standing.
• To assess the influence of surface tilt duration on this balance control mechanism.
• To test hypotheses regarding the role of force cues in balance control.

Main Methods:

• Measured anteroposterior body sway in response to short- and long-duration surface tilts.
• Interpreted sway responses using balance control models.
• Fit four feedback control model variants to experimental data to identify slow dynamics mechanisms.

Main Results:

• Model variants incorporating force cues provided the best fit to experimental sway data, especially for long-duration tilts.
• Results support the use of integrated foot and leg force afferents in a slow, positive feedback mechanism for upright standing.
• This positive torque feedback mechanism is consistent with self-calibration principles.

Conclusions:

• Humans employ a slow, positive feedback mechanism utilizing force sensory information from the feet and legs to maintain upright stance.
• This mechanism contributes to reducing body sway at very low frequencies.
• Despite long stimulus durations (~180s), precise estimation of some mechanism properties remains challenging.