Forefoot, rearfoot and shank coupling: Effect of variations in speed and mode of gait Michael B. Pohl a, * , Neil Messenger a , John G. Buckley b a School of Sport and Exercise Sciences, University of Leeds, Leeds LS2 9JT, UK b Vision and Mobility Research Laboratory, Department of Optometry, University of Bradford, Bradford BD7 1DP, UK Received 2 November 2005; received in revised form 16 March 2006; accepted 14 April 2006 Abstract Background: Although there is a wealth of research into the kinematic coupling between the foot and shank, it remains unclear whether the relationship is stable across speed and mode of gait. The aim of this study was to determine whether the coupling relationship between the forefoot, rearfoot and shank differed between walking and running, and across different running speeds. Methods: Twelve subjects walked/ran barefoot over-ground at one walking and three running speeds. The shank, rearfoot and forefoot were modelled as rigid segments and three-dimensional joint kinematics were determined using a seven camera ProReflex system. Coupling between the forefoot, rearfoot and shank was assessed using cross-correlation and vector coding techniques. Findings: Cross-correlation of rearfoot eversion/inversion with shank internal/external rotation was lower in walking (r = 0.49) compared to running (r > 0.95). This was also the case between rearfoot frontal plane and forefoot sagittal plane motion (walking, r = 0.80; running, r = 0.96). Rearfoot frontal plane and forefoot transverse plane cross-correlation was high in both running and walking (r > 0.90), but there was little evidence of any coupling between rearfoot frontal plane and forefoot frontal plane motion in any condition. No differences in cross- correlations were found between the three running speeds. Interpretation: Kinematic coupling between the forefoot, rearfoot and shank was weak during walking relative to running. In particular, the low cross-correlation between rearfoot eversion/inversion and shank internal/external rotation during walking implies the two motions are not rigidly linked, as has been assumed in previous injury models. # 2006 Elsevier B.V. All rights reserved. Keywords: Forefoot; Rearfoot; Kinematic coupling; Shank rotation; Gait 1. Introduction The link between subtalar joint pronation and shank internal rotation has long been a focus of injury research due to the theory that the two segments are kinematically coupled as a consequence of anatomy at the ankle-joint complex [1]. Subtalar pronation is described as a triplanar movement consisting of eversion, abduction and dorsiflex- ion. It has been suggested that the main component of subtalar pronation, rearfoot frontal plane motion (eversion/ inversion), is transferred into transverse tibial rotation (internal/external) [2]. Consequently, abnormal foot move- ments can alter normal kinematics and kinetics of the lower limb, resulting in increased risk of injury to bone and/or soft tissue structures [3,4]. Although extensive research into kinematic coupling between the foot and shank exists, it remains unclear whether the relationship is stable across different speeds and modes of gait. For example, inconsistencies appear between walking and running in terms of kinematic coupling at the subtalar joint. During running, research has shown the general pattern of motion as being rearfoot eversion accompanied by shank internal rotation during the first half of stance, with these motions reversed during the latter half of stance [5,6]. However, evidence indicating a similar kinematic coupling relationship during walking is less compelling. While studies generally agree that the shank www.elsevier.com/locate/gaitpost Gait & Posture 25 (2007) 295–302 * Corresponding author. Tel.: +1 302 831 4646; fax: +1 302 831 4234. E-mail address: pohl@udel.edu (M.B. Pohl). 0966-6362/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.gaitpost.2006.04.012