Goodworth - 2010 - Influence of stance width on frontal plane postural dynamics ...

Citation

Goodworth AD, Peterka RJ. Influence of stance width on frontal plane postural dynamics and coordination in human balance control. J Neurophysiol. 2010 Apr;Preprint. PUBMED

10 Word Summary

All stance widths have upper and lower body move in phase for lower frequency and out of phase at high frequency.

Abstract

The influence of stance width on frontal plane postural dynamics and coordination in human bipedal stance was investigated. We tested the hypothesis that when subjects adopt a narrow stance width, they will rely heavily on nonlinear control strategies and coordinated counter-phase upper and lower body motion to limit center-of-mass (CoM) deviations from upright; but as stance increases, the use of these strategies will diminish. Freestanding frontal plane body sway was evoked through continuous pseudorandom rotations of the support surface upon which subjects stood with various stimulus amplitudes. Subjects were either eyes open or closed and adopted various stance widths. Upper body, lower body, and CoM kinematics were summarized using root-mean-square and peak-to-peak measures and dynamic behavior was characterized using frequency-response and impulse-response functions. In narrow stance, CoM frequency-response function gains were reduced with increasing stimulus amplitude and in EO compared to EC; but in wide stance, gain reductions were much less pronounced. Results show that the narrow stance postural system is nonlinear across stimulus amplitude in both EO and EC conditions while the wide stance postural system is more linear. The nonlinearity in narrow stance is likely due to an amplitude-dependent sensory reweighting mechanism. Finally, lower body and upper body sway were approximately in-phase at low frequencies (<1 Hz) and out-of-phase at high frequencies (>1 Hz) across all stance widths and results were therefore inconsistent with the hypothesis that subjects made greater use of coordinated counter-phase upper and lower body motion in narrow compared to wide stance conditions.

Notes

• Hypothesis: Narrow stance uses non-linear control and upper and lower body move antiphase, while wide stance does not have this.
• Wide stance is less affected (compared to narrow) by eyes open/closed as perturbations increase.
• Upper body and lower body were in phase at low frequency and out of phase at high frequency across stance widths.
• Three possible ways of maintaining balance:
  • Limit motion between individual body segments and regulate CoM based on sensitivity to perturbation
  • All larger motion between body segments and limit CoM motion
  • Increase the base-of-support
• Subjects underwent platform rotations.
• Pseudorandom ternary sequence of rotations from 1-4°.
• Subjects appear to use visual information to reduce their upper body sway