Vibration-induced post-effects: A means to improve postural asymmetry in lower leg amputees? C. Duclos a,b, * , R. Roll a , A. Kavounoudias a , J.-P. Roll a , R. Forget b a Laboratoire de Neurobiologie Humaine, UMR 6149 Universite ´ de Provence/CNRS, Centre St Charles, Pole 3C, Case B, 3, Place Victor Hugo, 13331 Marseille Cedex 03, France b Centre de Recherche Interdisciplinaire en Re ´adaptation, Institut de Re ´adaptation de Montre ´al, 6300 Ave Darlington, Montre ´al, Que., Canada H3S 2J4 Received 28 April 2006; received in revised form 30 November 2006; accepted 16 December 2006 Abstract Muscle vibration has been shown to induce long-lasting and oriented alteration of standing posture in healthy individuals. The postural alterations can last several minutes following the end of vibration and are called post-effects. The goal of this study was to determine whether persons with lower leg amputation that show persistent postural asymmetry after usual rehabilitation experience these postural post-effects and if this could improve their weight bearing on the prosthesis. Centre of pressure (CP) position during stance was recorded prior to and up to 13 min after a 30 s unilateral vibration applied during sitting to lateral neck (trapezius) or hip (gluteus medius) muscles in 14 individuals with unilateral lower leg amputation and 18 controls. The amputees’ postural asymmetry was confirmed prior to the vibration intervention. A CP displacement, without an increase in CP velocity, was observed in both groups of participants over the 13 min post-vibration. For both the neck or hip vibration sites, the CP shifts were directed in the medio-lateral plane and were oriented either towards the vibrated side or the opposite side across subjects. This led to a decrease of postural asymmetry in half of the group of amputees. Within subject, the orientation of the post-effect was constant and changed to the opposite direction with vibration of the opposite body side. It is suggested that the post-effects are produced by a change of the postural reference consequent to the sustained proprioceptive message induced during the muscle vibration period. The orientation of the post-effects is discussed in relation to the notion of reference frame preference. All in all, because post-effect orientation is constant within subject and adaptive, future studies should investigate if individuals with lower leg amputation could benefit from postural post-effects induced by muscle vibration to improve function. # 2006 Elsevier B.V. All rights reserved. Keywords: Post-effect; Vibration; Amputees; Postural reference; Proprioception 1. Introduction The clinical observation of postural asymmetry has been noted in the rehabilitation process of persons with unilateral lower limb amputation leading to the goal of improving symmetrical weight bearing on both the remaining limb and the prosthesis. This asymmetry has been confirmed by studies that demonstrated a shift of the centre of pressure towards the non-amputated leg thus indicating preferred standing on the non-amputated leg [1–4]. Amputees need to achieve maximum prosthetic weight bearing because it is a good indicator of walking velocity and thus of potential functional ability following rehabilita- tion [5]. Furthermore, it has been suggested that the additional stress imposed by the augmented weight bearing on the non-amputated leg could be at the origin of difficulties often reported in this population such as pain in the back and in the non-amputated leg [6] as well as increased circulatory problems reported by patients with vascular disease [3]. The consequences of this asymmetry thus threaten amputees’ functional abilities and long-term quality of life [6]. Unfortunately, its correction has been www.elsevier.com/locate/gaitpost Gait & Posture 26 (2007) 595–602 * Corresponding author at: Centre de Recherche Interdisciplinaire en Re ´adaptation, Institut de Re ´adaptation de Montre ´al, 6300 Ave Darlington, Montre ´al, Que., Canada H3S 2J4. Tel.: +1 514 340 2111x3151; fax: +1 514 340 2154. E-mail address: cyril.duclos@umontreal.ca (C. Duclos). 0966-6362/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.gaitpost.2006.12.005