Altered postural control in anticipation of postural instability in persons with recurrent low back pain Simon Brumagne * , Lotte Janssens, Evelien Janssens, Lieselotte Goddyn Musculoskeletal Research Unit, Department of Rehabilitation Sciences, Faculty of Kinesiology and Rehabilitation Sciences, University of Leuven, Tervuursevest 101, B-3001 Leuven, Brabant, Belgium Received 3 January 2007; received in revised form 1 April 2008; accepted 21 April 2008 Abstract Insight into the mechanisms of altered postural control in persons with low back pain (LBP) could lead to better interventions for patients with LBP. This study investigated (1) whether persons with recurrent LBP have an altered body inclination, and (2) whether anticipation of postural instability further alters body inclination. Thirty-three young healthy individuals and 56 young persons with recurrent LBP participated in this study. The upright standing posture was evaluated by means of two piezo-resistive electrogoniometers and a force platform for the conditions as follows: (1) quiet stance with and without vision, and (2) in anticipation of postural instability due to a ballistic arm movement or ankle muscle vibration. No differences in body inclination were observed when visual information was available between the two groups (P > 0.05). However, significant more forward inclination was seen in the persons with recurrent LBP when vision was occluded (+7.4%) and in anticipation of postural instability (+19%) (P < 0.05) compared to the healthy individuals. The results suggest that young persons with recurrent LBP have an altered body inclination that might be caused by anticipation of postural instability. The adopted forward inclined posture may potentially be a factor in the recurrence of LBP. # 2008 Elsevier B.V. All rights reserved. Keywords: Proprioception; Postural balance; Subjective vertical; Low back pain 1. Introduction Alterations in postural control have been reported in persons with low back pain (LBP). Compared with healthy controls, persons with LBP demonstrated a greater postural sway, an increased difficulty with adapting to changing conditions, and a decreased recovery of postural balance after perturbation [1–3]. Furthermore, persons with LBP seem to have altered proprioceptive sensitivity. Due to a less refined position sense of the lower back [4,5], reweighting of the proprioceptive input by increas- ing the gain at the ankle level seems to have taken place in persons with LBP [6,7], so that people with LBP tend to use less hip and low back movement for balance control in quiet standing [6–9]. The vertical orientation of the body in the upright standing position is maintained by a dynamic interplay of vision, proprioception, haptic contact cues, efferent control and internal models [10,11]. Sensory inflow is compared to the subjective vertical, the internal representation of verticality. On the basis of the comparison, compensatory reorientations of the body are performed with the aim of keeping the body longitudinal axis aligned with the vertical. The subjective vertical is also updated every time sensory inflow changes [12]. In patients with musculoskeletal impairments such as spasmodic torticollis (i.e., a pathological condition whereby torsion of the cervical spine due to neck muscle spasm occurs) changes in the reference system used in the control of body orientation have been demonstrated [13]. A small number of studies have reported alterations in the body inclination in relation to postural control in persons with LBP [1,2,6] despite the clinical relevance. However, the results have been inconsistent, with evidence supporting www.elsevier.com/locate/gaitpost Available online at www.sciencedirect.com Gait & Posture 28 (2008) 657–662 * Corresponding author. Tel.: +32 16 329121; fax: +32 16 329197. E-mail address: simon.brumagne@faber.kuleuven.be (S. Brumagne). 0966-6362/$ – see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.gaitpost.2008.04.015