Postural changes after sustained neck muscle contraction in persons with a lower leg amputation Cyril Duclos a,b,c, * , Re ´gine Roll a , Anne Kavounoudias a , Jean-Philippe Mongeau b,c , Jean-Pierre Roll a , Robert Forget b,c a Laboratoire de Neurobiologie Humaine, UMR/CNRS 6149, Aix-Marseille Universite ´s, 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, QC, Canada H3S 2J4 c E ´ cole de Re ´adaptation, Faculte ´ de Me ´decine, Universite ´ de Montre ´al, C.P. 6128, Succ. Centre-ville, Montre ´al, QC, Canada H3C 3J7 Received 11 October 2007; received in revised form 9 April 2008; accepted 9 April 2008 Abstract Lower leg amputation generally induces asymmetrical weight-bearing, even after rehabilitation treatment is completed. This is detri- mental to the amputees’ long term quality of life. In particular, increasing strains on joint surfaces that receive additional weight load causes back and leg pain, premature wear and tear and arthritis. This pilot study was designed to determine whether subjects with lower leg amputation experience postural post-effects after muscle contraction, a phenomenon already observed in healthy subjects, and whether this could improve the weight-bearing on their prosthesis. Fifteen subjects with a unilateral lower leg amputation and 17 control subjects volunteered to participate in this study. Centre of pres- sure (CP) position was recorded during standing posture, under eyes closed and open conditions. Recordings were carried out before the subjects performed a 30-s voluntary isometric lateral neck muscle contraction, and again 1 and 4 min after the contraction. Postural post-effects characterized by CP shift, occurred in the medio-lateral plane in the majority of the amputated (7/15 eyes closed, 9/15 eyes open) and control (9/17 eyes closed, 11/17 eyes open) subjects after the contraction. Half of these subjects had a CP shift towards the side of the contraction and the other half towards the opposite side. In four amputated subjects tested 3 months apart, shift direction remained constant. These postural changes occurred without increase in CP velocity. Thus, a 30-s voluntary isometric contraction can change the standing posture of persons with lower leg amputation. The post-effects might result from the adaptation of the postural frame of reference to the proprioceptive messages associated with the isometric contraction. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Lower leg amputation; Postural asymmetry; Isometric contraction; Post-effects; Proprioception; Vision 1. Introduction Training for symmetrical weight-bearing is an important issue in the rehabilitation of persons with unilateral lower limb amputation. It is motivated by frequent clinical obser- vations of an asymmetrical weight-bearing in addition to laboratory measures confirming that more weight is taken on the non-amputated leg (Fernie and Holliday, 1978; Geurts et al., 1992; Hermodsson et al., 1994; Isakov et al., 1992). Altered force platform centre of pressure (CP) mea- sures have also been demonstrated in persons with lower leg amputation. Increased anterior–posterior and medio-lat- eral CP oscillations have been shown (Fernie and Holliday, 1978; Geurts et al., 1992; Hermodsson et al., 1994; Isakov et al., 1992) while others reported decreased oscillations (Gau- thier-Gagnon et al., 1986; Vittas et al., 1986). 1050-6411/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jelekin.2008.04.007 * Corresponding author. Address: Centre de Recherche Interdiscipli- naire en Re ´adaptation, Institut de Re ´adaptation de Montre ´al, 6300 Ave Darlington, Montre ´al, QC, Canada H3S 2J4. Tel.: +1 514 340 2111x3151; fax: +1 514 340 2154. E-mail address: cyril.duclos@umontreal.ca (C. Duclos). Available online at www.sciencedirect.com Journal of Electromyography and Kinesiology xxx (2008) xxx–xxx www.elsevier.com/locate/jelekin ARTICLE IN PRESS Please cite this article in press as: Duclos C et al., Postural changes after sustained neck muscle contraction ..., J Electromyogr Ki- nesiol (2008), doi:10.1016/j.jelekin.2008.04.007