The Journal of Neurophysiology Vol. 83 No. 5 May 2000, pp. 2980-2986
Copyright ©2000 by the American Physiological Society

A Fibers Mediate Cutaneous Reflexes During Human Walking

 ¹Department of Medical Physics and Biophysics, University of Nijmegen, NL-6525 EZ Nijmegen;  ²Institute of Neurology and  ³Department of Child Neurology, University Hospital Nijmegen, NL-6500 HB Nijmegen; and  ⁴SMK Research, NL-6500 GM Nijmegen, The Netherlands

van Wezel, B.M.H., B.G.M. van Engelen, F.J.M. Gabreëls, A.A.W.M. Gabreëls-Festen, and J. Duysens. A Fibers Mediate Cutaneous Reflexes During Human Walking. J. Neurophysiol. 83: 2980-2986, 2000. During human gait, transmission of cutaneous reflexes from the foot is controlled specifically according to the phase of the step cycle. These reflex responses can be evoked by nonnociceptive stimuli, and therefore it is thought that the large-myelinated and low-threshold A afferent fibers mediate these reflexes. At present, this hypothesis is not yet verified. To test whether A fibers are involved the reflex responses were studied in patients with a sensory polyneuropathy who suffer from a predominant loss of large-myelinated A fibers. The sural nerve of both patients and healthy control subjects was stimulated electrically at a nonnociceptive intensity during the early and late swing phases while they walked on a treadmill. The responses were studied by recording electromyographic (EMG) activity of the biceps femoris (BF) and tibialis anterior (TA) of the stimulated leg. In both phases, large facilitatory responses were observed in the BF of the healthy subjects. These facilitations were reduced significantly in the BF of the patients, indicating that A fibers mediate these reflexes. In TA similar results were obtained. The absolute response magnitude across the two phases was significantly smaller for the patients than for the healthy subjects. The TA responses for the healthy subjects were on average facilitatory during early swing and suppressive during end swing. Both facilitations and suppressions were considerably smaller for the patients, indicating that both types of responses are mediated by A fibers. It is concluded that low-threshold A sensory fibers mediate these reflexes during human gait. The low threshold and the precise phase-dependent control of these responses suggest that these responses are important in the regulation of gait. The loss of such reflex activity may be related to the gait impairments of these patients.