Postural propioceptive

Journal of Physiology (1992), 458. pp. 69-83 With 6 figures Printed in Great Britain

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POSTURAL PROPRIOCEPTIVE REFLEXES IN STANDING HUMAN SUBJECTS: BANDWIDTH OF RESPONSE AND TRANSMISSION CHARACTERISTICS

BY RICHARD C. FITZPATRICK, ROBERT B. GORMAN, DAVID BURKE AND SIMON C. GANDEVIA From the Prince of Wales Medical Research Institute, University of New South Wales and the Department ofNeurology, The Prince Henry and Prince of Wales Hospitals, Sydney 2036, Australia

(Received 15 October 1991)
SUMMARY

1. This study investigated the reflex control of postural sway during human bipedal stance. The experiments were designed to: (i) find evidence for the operation of 'stretch reflex' pathways during quiet stance, (ii) determine the bandwidth of the reflex response, (iii)describe the reflex transmission characteristics in standing subjects, and (iv) assess the ability of subjects to make a task-dependent change in the reflex. 2. A continuous ranidom perturbation that did not threaten stability was applied at waist level to nine staiiding subjects. The effects of the perturbation on ankle torque, ankle movement and soleus electromyographic activity (EMG) were identifiedby cross-correlation. The bandwidth of the reflex response and the transmission characteristics of reflexes that respond to ankle movement were identified by spectral analysis. Changes in these reflex responses were investigated when subjects attempted to stand as still as possible, had their eyes closed, or balanced a load equivalent to their own body in a situation in which neither visual norvestibular reflexes would be activated. 3. When standing, a reflex response coherent with the perturbation was seen in soleus EMG at frequencies up to 5 Hz, with mnaximal coherence at 1V0-2 0 Hz. Reflex gain increased with frequency, and there was a frequency-dependent phase advance of soleus EMG on ankle movement reaching 135 deg at 3 Hz. When attempting to minimize sway, subjects produced a morecoherent reflex response and significantly increased reflex gain. 4. The response and transmission characteristics of the lower limb proprioceptive reflex in freely standing subjects were similar to those in subjects balancing a load at the ankle, a situation in which vestibular and visual inputs could not contribute. 5. It is concluded that reflex feedback related to ankle movement contributessignificantly to maintaining stance, and that much of the reflex response originates from lower limb mechanoreceptors stimulated by ankle rotation. Although reflex gain may be relatively low during quiet stance it can be increased when necessary to maintain stability.
MS 9817

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R. C. FITZPATRICK AND OTHERS
INTRODUCTION

During human bipedal stance, body movements and external disturbancesapply continuous perturbing torques at the ankles. If balance is to be maintained, those perturbations which might destabilize posture must be opposed by co-ordinated responses from leg muscles. Previous studies of human stance have generally used abrupt and often large disturbances of the standing posture to investigate these reflexes (Nashner, 1976, 1977; Bussel, Katz, Pierrot-Deseilligny,Bergego & Hayat, 1980; Diener, Dichgans, Bootz & Backer, 1984; Dietz, Quintern, Berger & Schenck, 1985; Dietz, Horstmann & Berger, 1989; Nardone, Giordano, Corra & Schieppati, 1990). Other studies have used electrical stimulation of peripheral nerves and measured H-reflex responses (Katz, Meunier & Pierrot-Deseilligny, 1988), or the effects of non-muscular afferent discharge on motoneuron excitability(Aniss, Diener, Hore, Burke & Gandevia, 1990). These studies have identified and measured the latencies of visual, vestibular and proprioceptive reflexes which may operate to maintain upright human stance. However, the large synchronized neural discharges evoked by these stimuli could reflect only those physiological mechanisms designed to prevent falling, rather than the operation of the motor...