Contents lists available at ScienceDirect Neuroscience Letters journal homepage: www.elsevier.com/locate/neulet Research article Task difficulty has no effect on haptic anchoring during tandem walking in young and older adults Andréia Abud da Silva Costa a,b , Luciana Oliveira dos Santos a,b , Eliane Mauerberg-deCastro c , Renato Moraes b, ⁎ a Ribeirão Preto Medical School, Graduate Program in Rehabilitation and Functional Performance, University of São Paulo, Brazil b Biomechanics and Motor Control Lab, School of Physical Education and Sport of Ribeirão Preto, University of São Paulo, Brazil c Department of Physical Education, Biosciences Institute, São Paulo State University, Brazil ARTICLE INFO Keywords: Older adults Anchor system Haptic information Trunk acceleration Tandem gait Balance beam ABSTRACT This study assessed the contribution of the “anchor system’s” haptic information to balance control during walking at two levels of difficulty. Seventeen young adults and seventeen older adults performed 20 randomized trials of tandem walking in a straight line, on level ground and on a slightly-raised balance beam, both with and without the use of the anchors. The anchor consists of two flexible cables, whose ends participants hold in each hand, to which weights (125 g) are attached at the opposing ends, and which rest on the ground. As the par- ticipants walk, they pull on the cables, dragging the anchors. Spatiotemporal gait variables (step speed and single- and double-support duration) were processed using retro-reflective markers on anatomical sites. An accelerometer positioned in the cervical region registered trunk acceleration. Walking on the balance beam increased single- and double-support duration and reduced step speed in older adults, which suggests that this condition was more difficult than walking on the level ground. The anchors reduced trunk acceleration in the frontal plane, but the level of difficulty of the walking task showed no effect. Thus, varying the difficulty of the task had no influence on the way in which participants used the anchor system while tandem walking. The older adults exhibited more difficulty in walking on the balance beam as compared to the younger adults; however, the effect of the anchor system was similar in both groups. 1. Introduction When compared to young adults, older adults show an increase in frontal plane sway during walking due to difficulties in medial-lateral balance control [1], which increases the risk for falls [2]. Previous studies that analyzed gait patterns found that trunk variability increases with age [3,4] and discriminates between healthy and frail older adults [5]. Recently, we investigated how additional haptic information that an “anchor system” provides [6]affects older adults’ trunk sway during tandem walking on the ground in a straight line (i.e., placing one foot in front of the other) [7]. Acceleration in the frontal plane was reduced when participants used the anchors. The anchor system, a non-rigid tool designed to help reduce body sway, has been studied in different groups, including older adults [7,8,9], with the purpose of testing the extent of the integration of haptic cues by the postural control system, whether in static balance tasks or dynamic locomotion tasks. The anchor consists of a flexible cable held in each hand, with an endpoint attached to a light mass, which is kept in contact with a surface (typically, the floor or ground) [6]. During proper use of the anchors, the cable should be kept taut and the mass should touch the ground at all times. In balancing tasks, the dynamic interplay between the cables’ varying tensions and the con- tinuous hand-pulling adjustments and body oscillations is the source of the haptic input that the postural system integrates in order to reduce body sway [10]. The anchors provide information about spatial or- ientation of the body relative to the ground, which helps to maintain the trunk in the upright position [7,10]. Information, in this case, is understood as a pattern of a continuous flow of energy that specifies the environment’s constraints to the individual [10]. The effect of the anchors has been studied in quiet standing tasks in young and older adults [6,8,9]. However, the anchors have the poten- tial to be used in walking tasks [7,11,12]. This is important, since the most falls by older adults occur during walking [13]. Studies involving participants that lightly touched rigid and non-rigid surfaces while walking showed that additional haptic cues improve balance control [14,15,16]. Such tasks require the continuous touch of an individual’s https://doi.org/10.1016/j.neulet.2017.12.052 Received 8 May 2017; Received in revised form 20 December 2017; Accepted 23 December 2017 ⁎ Corresponding author at: Escola de Educação Física e Esporte de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes, 3900, Ribeirão Preto, SP, Brazil. E-mail address: renatomoraes@usp.br (R. Moraes). Neuroscience Letters 666 (2018) 133–138 Available online 26 December 2017 0304-3940/ © 2017 Elsevier B.V. All rights reserved. T