Journal of Neurophysiology, Vol 72, Issue 6 2892-2902, Copyright © 1994 by APS

ARTICLES

Modification of postural responses and step initiation: evidence for goal-directed postural interactions

A. L. Burleigh, F. B. Horak and F. Malouin
R. S. Dow Neurological Sciences Institute, Portland, Oregon 97209.

1. In this study, the interaction between anticipatory postural adjustments for step initiation and automatic postural responses to an external perturbation were investigated by having subjects initiate a voluntary forward step while perturbed by a backward surface translation, which caused forward sway of the body. The postural adjustments for step initiation act to move the body center of mass (COM) forward, whereas the automatic postural responses act to move the COM backward to restore stance equilibrium. Because the postural behaviors are in opposition, we asked whether a temporal hierarchy exists in which automatic postural responses are executed to restore equilibrium and followed by stereotypic postural adjustments for step initiation, or whether the interaction between these two postural behaviors is more dynamic. 2. Lower extremity electromyographs (EMGs), ground reaction forces, and kinematics were recorded from 10 subjects during three conditions: to quantify the anticipatory postural adjustments for step initiation, subjects stepped forward as soon as they felt a proprioceptive cue; to quantify the automatic postural responses to perturbation, subjects maintained stance equilibrium in response to a backward surface translation under both feet; and to quantify the interaction between the postural adjustments for the voluntary step and the automatic responses to the perturbation, subjects were exposed to a backward surface translation and instructed to step forward as soon as they felt the platform begin to move. 3. The anticipatory adjustments for step initiation included tibialis activation [stance limb = 163 +/- 28 (SE) ms; swing limb = 173 +/- 33 ms] and soleus inhibition resulting in center of foot pressure (COP) moving backward and lateral toward the swing limb to propel the COM forward over the stance limb. Subsequently, activation of the swing limb gastrocnemius resulted in heel-off. In contrast, the automatic postural adjustments for maintenance of stance equilibrium during a backward surface translation included activation of soleus and gastrocnemius (104 +/- 23 ms and 115 +/- 14 ms, respectively) resulting in a symmetrical forward displacement of the COP that moved the COM back to its original position with respect to the feet. 4. When a forward step was initiated in response to the translation, the automatic postural responses were reduced in amplitude bilaterally in soleus and in the stance limb gastrocnemius. When present the postural response occurred at the same latency when the goal was to initiate a step as when the goal was to maintain standing.(ABSTRACT TRUNCATED AT 400 WORDS)

This article has been cited by other articles:

				L. B. Oude Nijhuis, B. R. Bloem, M. G. Carpenter, and J. H. J. Allum Incorporating Voluntary Knee Flexion Into Nonanticipatory Balance Corrections J Neurophysiol, November 1, 2007; 98(5): 3047 - 3059. [Abstract] [Full Text] [PDF]

				T. W Cacciatore, F. B Horak, and S. M Henry Improvement in Automatic Postural Coordination Following Alexander Technique Lessons in a Person With Low Back Pain Physical Therapy, June 1, 2005; 85(6): 565 - 578. [Abstract] [Full Text] [PDF]

				B. Schepens and T. Drew Independent and Convergent Signals From the Pontomedullary Reticular Formation Contribute to the Control of Posture and Movement During Reaching in the Cat J Neurophysiol, October 1, 2004; 92(4): 2217 - 2238. [Abstract] [Full Text] [PDF]

				B. Schepens and T. Drew Strategies for the Integration of Posture and Movement During Reaching in the Cat J Neurophysiol, November 1, 2003; 90(5): 3066 - 3086. [Abstract] [Full Text] [PDF]

				R. Grasso, M. Zago, and F. Lacquaniti Interactions Between Posture and Locomotion: Motor Patterns in Humans Walking With Bent Posture Versus Erect Posture J Neurophysiol, January 1, 2000; 83(1): 288 - 300. [Abstract] [Full Text] [PDF]

				V. S. Mercer and S. A Sahrmann Postural Synergies Associated With a Stepping Task Physical Therapy, December 1, 1999; 79(12): 1142 - 1152. [Abstract] [Full Text] [PDF]

				S. M. Henry, J. Fung, and F. B. Horak EMG Responses to Maintain Stance During Multidirectional Surface Translations J Neurophysiol, October 1, 1998; 80(4): 1939 - 1950. [Abstract] [Full Text] [PDF]