HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 97/5/3639    most recent 01272.2006v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (9) Citing Articles via Google Scholar Google Scholar Articles by van der Linden, M. H. Articles by Duysens, J. Search for Related Content PubMed PubMed Citation Articles by van der Linden, M. H. Articles by Duysens, J.

Muscle Reflexes and Synergies Triggered by an Unexpected Support Surface Height During Walking

¹Department of Rehabilitation Medicine, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands; ²Gait and Posture Laboratory, Department of Kinesiology, University of Waterloo, Waterloo, Canada; and ³Sint Maartenskliniek Research Development & Education, Nijmegen, The Netherlands

Submitted 5 December 2006; accepted in final form 23 March 2007

An important phase in the step cycle is foot contact. When the moment of foot contact differs from the one expected, a fast response is needed. Such a mismatch can be caused by hitting a support surface earlier or later than expected. To study this, experiments were performed with healthy young adults who walked on a platform that was unexpectedly at a lowered (5 cm) or at a level height. Glasses blocked the lower visual field. In the unexpectedly lowered trials, the absence of expected heel contact triggered responses in the ipsilateral anti-gravity muscles [ipsilateral medial gastrocnemius (MGi), ipsilateral rectus femoris (RFi)] and contralateral flexor muscles [contralateral tibialis anterior (TAc), contralaterial biceps femoris (BFc)] with latencies of 47–69 ms. After the delayed heel contact, enhanced activity was found in the MGi, RFi, and TAc muscles. This specific muscle synergy was presumably activated to arrest the forward propulsion of the body. In contrast, when the surface was unexpectedly at level height, the subjects expected to step down, and the leg briefly yielded. A muscle synergy was activated at 46–81 ms that flexed the ipsilateral knee (TAi, BFi, RFi) and extended the contralateral one (MGc, BFc) to unload the perturbed leg and delay the contralateral swing phase. Both conditions triggered a fast functionally relevant muscle synergy because of a mismatch between the expected and actual sensory feedback at the moment of foot contact. The results are consistent with an internal model that compares the expected with the actual sensory feedback. The short latency of the response suggests a subcortical, possibly cerebellar pathway.

This article has been cited by other articles:

				J. Shemmell, J. H. An, and E. J. Perreault The Differential Role of Motor Cortex in Stretch Reflex Modulation Induced by Changes in Environmental Mechanics and Verbal Instruction J. Neurosci., October 21, 2009; 29(42): 13255 - 13263. [Abstract] [Full Text] [PDF]

				M. H. van der Linden, D. de Kam, B. G. M. van Engelen, H. T. Hendricks, and J. Duysens Fast Responses to Stepping on an Unexpected Surface Height Depend on Intact Large-Diameter Nerve Fibers: A Study on Charcot-Marie-Tooth Type 1A Disease J Neurophysiol, September 1, 2009; 102(3): 1684 - 1698. [Abstract] [Full Text] [PDF]

				R. af Klint, J. B. Nielsen, T. Sinkjaer, and M. J. Grey Sudden Drop in Ground Support Produces Force-Related Unload Response in Human Overground Walking J Neurophysiol, April 1, 2009; 101(4): 1705 - 1712. [Abstract] [Full Text] [PDF]

				D. S. Marigold and J. E. Misiaszek Whole-Body Responses: Neural Control and Implications for Rehabilitation and Fall Prevention Neuroscientist, February 1, 2009; 15(1): 36 - 46. [Abstract] [PDF]