TY - JOUR
T1 - A unified view of quiet and perturbed stance
T2 - Simultaneous co-existing excitable modes
AU - Creath, Robert
AU - Kiemel, Tim
AU - Horak, Fay
AU - Peterka, Robert
AU - Jeka, John
N1 - Funding Information:
Supported by NIH Grant NS35070 and NIH Grant 1RO1NS046065 as part of the NSF/NIH Collaborative Research in Computational Neuroscience Program (J. Jeka), NIH grants RO1AG06457 and DC-01849 (F. Horak), and NIH grant AG17960 (R. Peterka).
PY - 2005/3/29
Y1 - 2005/3/29
N2 - When standing quietly, human upright stance is typically approximated as a single segment inverted pendulum. In contrast, investigations which perturb upright stance with support surface translations or visual driving stimuli have shown that the body behaves like a two-segment pendulum, displaying both in-phase and anti-phase patterns between the upper and lower body. Here we present evidence that a single-segment characterization of quiet stance is inadequate. Similar to perturbed stance, quiet stance has simultaneously co-existing in-phase and anti-phase patterns. Subjects stood with eyes closed in three sensory conditions: a fixed surface, a foam surface, and a sway-referenced surface. Spectral analysis showed that the body behaved like a multi-link pendulum with two co-existing modes. The angles of the trunk and leg segments were in-phase for frequencies below 1 Hz and anti-phase for frequencies above 1 Hz. The shift from in-phase to anti-phase sway showed an abrupt change for the fixed and foam surfaces, but a gradual change for the sway-referenced condition with the trunk showing a phase lead over the legs. The coexistence of in-phase and anti-phase patterns during quiet stance suggests that the ankle and hip strategies are not extremes along a behavioral continuum of mixed strategies. They are "simultaneously co-existing excitable modes", both always present, but one of which may predominate depending upon the characteristics of the available sensory information, task or perturbation.
AB - When standing quietly, human upright stance is typically approximated as a single segment inverted pendulum. In contrast, investigations which perturb upright stance with support surface translations or visual driving stimuli have shown that the body behaves like a two-segment pendulum, displaying both in-phase and anti-phase patterns between the upper and lower body. Here we present evidence that a single-segment characterization of quiet stance is inadequate. Similar to perturbed stance, quiet stance has simultaneously co-existing in-phase and anti-phase patterns. Subjects stood with eyes closed in three sensory conditions: a fixed surface, a foam surface, and a sway-referenced surface. Spectral analysis showed that the body behaved like a multi-link pendulum with two co-existing modes. The angles of the trunk and leg segments were in-phase for frequencies below 1 Hz and anti-phase for frequencies above 1 Hz. The shift from in-phase to anti-phase sway showed an abrupt change for the fixed and foam surfaces, but a gradual change for the sway-referenced condition with the trunk showing a phase lead over the legs. The coexistence of in-phase and anti-phase patterns during quiet stance suggests that the ankle and hip strategies are not extremes along a behavioral continuum of mixed strategies. They are "simultaneously co-existing excitable modes", both always present, but one of which may predominate depending upon the characteristics of the available sensory information, task or perturbation.
KW - Ankle strategy
KW - Biomechanics
KW - Hip strategy
KW - Motor programs
KW - Posture
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U2 - 10.1016/j.neulet.2004.11.071
DO - 10.1016/j.neulet.2004.11.071
M3 - Article
C2 - 15740840
AN - SCOPUS:14644433007
SN - 0304-3940
VL - 377
SP - 75
EP - 80
JO - Neuroscience Letters
JF - Neuroscience Letters
IS - 2
ER -