Reducing gait speed affects axial coordination of walking turns Caroline Forsell a , David Conradsson a,b , Caroline Paquette c , Erika Franzén a,b, * a Karolinska Institutet, Department of Neurobiology, Care Sciences and Society, Division of Physiotherapy, Stockholm, Sweden b Function Area Occupational Therapy & Physiotherapy, Allied Health Professionals Function, Karolinska University Hospital, Stockholm, Sweden c Department of Kinesiology and Physical Education, McGill University and Centre for Interdisciplinary Research in Rehabilitation, Montreal, Canada A R T I C L E I N F O Article history: Received 19 October 2016 Received in revised form 5 February 2017 Accepted 20 February 2017 Keywords: Walking velocity Turning Axial coordination Older adults Speed dependent A B S T R A C T Turning is a common feature of daily life and dynamic coordination of the axial body segments is a cornerstone for safe and efficient turning. Although slow walking speed is a common trait of old age and neurological disorders, little is known about the effect of walking speed on axial coordination during walking turns. The aim of this study was to investigate the influence of walking speed on axial coordination during walking turns in healthy elderly adults. Seventeen healthy elderly adults randomly performed 180  left and right turns while walking in their self-selected comfortable pace and in a slow pace speed. Turning velocity, spatiotemporal gait parameters (step length and step time), angular rotations and angular velocity of the head and pelvis, head-pelvis separation (i.e. the angular difference in degrees between the rotation of the head and pelvis) and head-pelvis velocity were analyzed using Wilcoxon signed-rank tests. During slow walking, turning velocity was 15% lower accompanied by shorter step length and longer step time compared to comfortable walking. Reducing walking speed also led to a decrease in the amplitude and velocity of the axial rotation of the head and pelvis as well as a reduced head-pelvis separation and angular velocity. This study demonstrates that axial coordination during turning is speed dependent as evidenced by a more ‘en bloc’ movement pattern (i.e. less separation between axial segments) at reduced speeds in healthy older adults. This emphasizes the need for matching speed when comparing groups with diverse walking speeds to differentiate changes due to speed from changes due to disease. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Locomotion in everyday life is rarely performed during steady state walking; in fact, turning steps make up approximately 35– 45% of all steps during a typical day [1]. Turning is a complex task incorporating spatial awareness and maintenance of dynamic body stability, which in turn requires coordination of axial segments [2,3]. The dynamic features of axial coordination are not only important for safe and efficient turning [3] but also commonly affected by neurological disorders, such as Parkinson's disease [4,5] and stroke [6–8]. Reduced walking velocity is a common trait of old age [9,10] as well as in neurological disorders [11–14] and turning often causes falls in these populations [15,16]. Speed dependency of spatiotem- poral parameters and axial coordination are well documented during straight walking [17–20]. Previous studies on straight walking have demonstrated that slow walking leads to shorter and wider steps [17,18,20], as well as reduced axial movements and disturbed coordination [18,19]. However, few studies [21,22] have investigated the impact of velocity on walking turns. These studies primarily analyzed turning initiation, reporting a top-down temporal sequencing (i.e. head rotation precedes reorientation of the trunk, pelvis and foot displacement) independent of turning speed [21,22]. In addition, an altered inter-segmental pattern, where the head and pelvis move almost simultaneously, was observed in healthy adults walking substantially slower than their normal speed [22]. Although more commonly seen in Parkinson's disease [4,5] and stroke [6–8], this en-bloc movement strategy, has also been reported during whole-body turns or when turning at comfortable speed in healthy adults [23,24]. Our group [25] and others [21,26] have suggested, reducing degrees of freedom to facilitate movement control or minimize perturbation. Thus, it is unclear how decreased axial coordination is linked to specific diseases or strategy related to turning speed, making comparisons in axial coordination difficult between individuals with movement disorders and healthy controls who walk at different speeds. We * Corresponding author at: Division of Physiotherapy, Department of Neurobiol- ogy, Care Sciences and Society, Karolinska Institutet,141 83 Huddinge, Alfred Nobels Allé 23, 23100, Sweden. E-mail address: erika.franzen@ki.se (E. Franzén). http://dx.doi.org/10.1016/j.gaitpost.2017.02.020 0966-6362/© 2017 Elsevier B.V. All rights reserved. Gait & Posture 54 (2017) 71–75 Contents lists available at ScienceDirect Gait & Posture journal homepage: www.else vie r.com/locate /gait post