Locomotion pattern and foot pressure adjustments during gentle turns in healthy subjects

Abstract

People suffering from locomotor impairment find turning manoeuvres more challenging than straight-ahead walking. Turning manoeuvres are estimated to comprise a substantial proportion of steps taken daily, yet research has predominantly focused on straight-line walking, meaning that the basic kinetic, kinematic and foot pressure adaptations required for turning are not as well understood. We investigated how healthy subjects adapt their locomotion patterns to accommodate walking along a gently curved trajectory (radius 2.75 m). Twenty healthy adult participants performed walking tasks at self-selected speeds along straight and curved pathways. For the first time for this mode of turning, plantar pressures were recorded using insole foot pressure sensors while participants’ movements were simultaneously tracked using marker-based 3D motion capture. During the steady-state strides at the apex of the turn, the mean operating point of the inside ankle shifted by 1 degree towards dorsiflexion and that for the outside ankle shifted towards plantarflexion. The largest change in relative joint angle range was an increase in hip rotation in the inside leg (>60%). In addition, the inside foot was subject to a prolonged stance phase and a 10% increase in vertical force in the posteromedial section of the foot compared to straight-line walking. Most of the mechanical change required was therefore generated by the inside leg with hip rotation being a major driver of the gentle turn. This study provides new insight into healthy gait during gentle turns and may help us to understand the mechanics behind some forms of impairment.

Introduction

The locomotor system of a healthy human is energy efficient, robust to disturbances, and is able to perform versatile types of movement (Devine, 1985). Turning manoeuvres are estimated to comprise a substantial proportion of steps taken daily (Glaister et al., 2007). However, while straight-ahead walking and running have been studied extensively, fewer studies have focused on any kinetic, kinematic or foot pressure adjustments associated with turning (Courtine and Schieppati, 2004, Courtine and Schieppati, 2003a, Courtine and Schieppati, 2003b, Dixon et al., 2014, Glaister et al., 2008, Hase and Stein, 1999, Orendurff et al., 2006, Strike and Taylor, 2009, Taylor et al., 2005). Turning manoeuvres pose greater demands on the locomotor system relative to straight-ahead walking as the kinetics and kinematics of the bilateral limbs become asymmetric, causing greater mediolateral instability (Courtine and Schieppati, 2003b, Patla et al., 1999). The biomechanics of turning merits further study as previous research has highlighted that the elderly (Thigpen et al., 2000), individuals with Parkinson’s disease (Guglielmetti et al., 2009), stroke patients (Godi et al., 2010) and transtibial amputees (Segal et al., 2011) struggle with turning in particular. Risks of falls and injuries are also greater during turning relative to straight ahead-walking (Cumming and Klineberg, 1994, Nevitt et al., 1991). A better understanding of how healthy people negotiate turns is important for identifying mechanisms underlying locomotor impairment.

Different types of turning manoeuvres are utilised during everyday activities (Glaister et al., 2007). Sharp turns, for example, are completed in just two to three steps, while more gentle turns require several steady-state (turn continuation) steps in between turn initiation and termination steps (Glaister et al., 2007). A variety of turning manoeuvres have, therefore, been investigated in a laboratory setting. Some studies have identified and focused on the two main strategies used to navigate sharp turns, namely ‘step’ and ‘spin’ turns, which are defined by the change in direction being away from and towards the side of the limb in stance, respectively (Akram et al., 2010, Huxham et al., 2006, Patla et al., 1999, Taylor et al., 2005). Other studies have investigated steady-state turning manoeuvres such as walking circular pathways (Godi et al., 2014, Segal et al., 2008, Turcato et al., 2015); curved trajectories (Courtine and Schieppati, 2003a, Orendurff et al., 2006); and U-Turns (Guldemond et al., 2007, Hase and Stein, 1999).

The footfall kinematics, joint angle ranges and forces acting through the feet have not yet been quantified simultaneously in a single set of subjects for any given turning manoeuvre. Of the few studies that have investigated the modulation of ground reaction forces and impulses during turning, most of which have used force plates (Glaister et al., 2008, Strike and Taylor, 2009, Taylor et al., 2005). Force plates allow the complete analysis of the ground reaction forces (horizontal and vertical), however one drawback with force plate setups is that the participants may adjust their walking pattern in order to plant the desired foot on the force plate area (Glaister et al., 2008, Strike and Taylor, 2009). The surface area of the force plates also limits the number of steps that can be measured, meaning that the majority of research into foot pressure adjustments during turning has focused on sharp turns completed in a few steps (Strike and Taylor, 2009, Taylor et al., 2005) and not gentle turns. One way to avoid this bias is to use insole pressure sensors as they do not influence the trajectory of the participant and allow data to be collected over a number of gait cycles. They allow the complete pressure map under the foot to be recorded but are unfortunately only capable of detecting normal forces (Turcato et al., 2015).

The purpose this study was to investigate any adjustments in vertical ground reaction forces and impulses during steady state gentle turning relative to straight-ahead walking in healthy subjects using insole foot pressure sensors for the first time. Additionally we sought to simultaneously quantify footfall kinematics and joint angle ranges using 3D motion capture for a more complete picture of gentle turning from a single sample of subjects. By using a gently curved pathway (radius ∼2.75 m) we aimed to capture steady-state (turn continuation) strides at the apex of the curve for the inside and outside legs.