Short communication Influence of gait speed on free vertical moment during walking Jérémie Begue ⇑ , Teddy Caderby, Nicolas Peyrot, Georges Dalleau Laboratoire IRISSE, UFR des Sciences de l’Homme et de l’Environnement, Université de la Réunion, 117 rue du Général Ailleret, 97430 Le Tampon, Ile de la Réunion, France article info Article history: Accepted 4 May 2018 Available online xxxx Keywords: Torque Ground reaction forces Torsional loading Lower limb rotation Transverse plane abstract Free vertical moment (FVM) of ground reaction is recognized to be a meaningful indicator of torsional stress on the lower limbs when walking. The purpose of this study was to examine whether and how gait speed influences the FVM when walking. Fourteen young healthy adults performed a series of overground walking trials at three different speeds: low, preferred and fast. FVM was measured during the stance phase of the dominant leg using a force platform embedded in a 10 m-long walkway. Transverse plane kinematic parameters of the foot and pelvis were measured using a motion capture system. Results showed a significant decrease in peak abduction FVM (i.e., resisting internal foot rotation) and an increase in peak adduction FVM (i.e., resisting external foot rotation), together with an increase in gait speed. Concomitantly, we observed a decrease in the foot progression angle and an increase in the peak pelvis rotation velocity in the transverse plane with an increase in gait speed. A significant positive correlation was found between the pelvis rotation velocity and the peak adduction moment, suggesting that pelvis rotation influences the magnitude of adduction FVM. Furthermore, we also found significant correlations between the peak adduction FVM and both the step length and frequency, indicating that the alterations in FVM may be ascribed to changes in these two key variables of gait speed. These speed-related changes in FVM should be considered when this parameter is used in gait assessment, particularly when used as an index for rehabilitation and injury prevention. Ó 2018 Elsevier Ltd. All rights reserved. 1. Introduction Analysis of ground reaction forces (GRF) is a classical approach for assessing gait in both the research and clinical fields. Indeed, GRF, which are usually measured by walking on a force platform, can be used to quantify the deviation of gait from normal and thus identify walking impairments (Andriacchi et al., 1977; Claeys, 1983). Such information is used, for instance, by physicians to select surgical or other therapeutic interventions for gait improve- ment and perform post-intervention follow-up procedures (Marasovic et al., 2009). The role of GRF in gait has been extensively studied in the liter- ature. The patterns formed by the three components of GRF (i.e., anteroposterior, mediolateral and vertical) and their changes with gait speed are also well known (e.g., Andriacchi et al., 1977; Nilsson and Thorstensson, 1989). However, much less attention has been paid to the free vertical moment (FVM) of ground reaction, which represents the torque that acts about the vertical axis that origi- nates at the foot’s centre of pressure (CoP) and results from shear forces between the foot and the ground (Holden and Cavanagh, 1991). Nonetheless, evidence suggests that FVM may be indicative of the torsional stress exerted on the lower limbs (Ohkawa et al., 2017; Yang et al., 2014), and that this parameter may provide use- ful clinical information for injury prevention (Hasan et al., 1991) and rehabilitation (Stan and Orban, 2014). It is generally recognized that FVM exhibits a biphasic shape during the stance phase of walking (Almosnino et al., 2009; Farahpour et al., 2016). This is characterized by an initial abduction moment (i.e., resisting the foot’s internal rotation) followed by an adduction moment (i.e., resisting external rotation) whose peak magnitude has been related to the torsion of the lower extremity (Ohkawa et al., 2017; Yang et al., 2014). However, to date little is known about the influence of gait speed on FVM. Indeed, although a study has shown that FVM pattern may change in conditions of fast walking (Li et al., 2001), it still remains to determine whether and how the magnitudes of the abduction and adduction peaks of FVM are influenced by gait speed. Such knowledge is important because these FVM parameters are used in clinical gait assessment (Hasan et al., 1991; Stan and Orban, 2014). The aim of this study was therefore to examine the influence of gait speed on the FVM when walking. https://doi.org/10.1016/j.jbiomech.2018.05.011 0021-9290/Ó 2018 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: jeremie.begue@univ-reunion.fr (J. Begue). Journal of Biomechanics xxx (2018) xxx–xxx Contents lists available at ScienceDirect Journal of Biomechanics journal homepage: www.elsevier.com/locate/jbiomech www.JBiomech.com Please cite this article in press as: Begue, J., et al. Influence of gait speed on free vertical moment during walking. J. Biomech. (2018), https://doi.org/ 10.1016/j.jbiomech.2018.05.011