Aging effects on object transport during gait § Gudrun Diermayr a , Tara L. McIsaac a , Terry R. Kaminski a , Andrew M. Gordon a,b, * a Department of Biobehavioral Sciences, Teachers College, Columbia University, New York, NY 10027, USA b Department of Rehabilitation Medicine, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA 1. Introduction Dexterous object manipulation relies on precise fingertip force control. Healthy young adults accurately adjust their grip (normal) forces to the object’s physical properties [1] and to inertial forces acting on the object resulting from movement in an anticipatory fashion [2–5]. For example, during self-initiated object movement, grip and inertial forces fluctuate in parallel to avoid delays associated with feedback control. This anticipatory force coupling maintains an adequate grip force safety margin against the object slipping as the inertial forces fluctuate [2–4]. A similar anticipatory force coupling is seen when holding an object during jumping [2] and walking [3,4,6]. Functional activities requiring dexterous object manipulation (e.g., preparing meals) become more difficult during aging [7] and increase dependency in daily life [8]. When older adults manipu- late objects, they use excessive grip forces [9–11]. This strategy can compensate for declines in tactile function and/or changes in skin slipperiness [9], but may result in fatigue or crushing of delicate objects [1]. Anticipatory grasp control, however, seems largely intact in older adults [9–11]. This is supported by findings of appropriate grip force scaling to object properties [9,11] and a tight grip-inertial force coupling during dynamic arm movements [10– 12]. Nevertheless, grip force delays within anticipatory control are seen as task demands increase [10]. Moreover, force tracking in older adults deteriorates when increasing task difficulty [13]; e.g., by adding a cognitive task [14]. Thus, intact anticipatory control may be associated with the simple nature of the tasks tested (minimal postural demands during sitting and/or focus of subjects’ attention exclusively on grasp [9,10,13,14]). In older adults, information processing deteriorates [15], and attentional requirements associated with locomotion increase [16]. Performing a secondary task concurrently thus adds more demands [16]. In healthy older adults, dual-task interference is marginal during simple, unperturbed walking, but becomes evident in challenging gait environments [17–19]: When crossing over obstacles, attentional resources must be redirected towards balance and the visuomotor system. This results in a decline in the Gait & Posture 34 (2011) 334–339 A R T I C L E I N F O Article history: Received 8 October 2010 Received in revised form 17 May 2011 Accepted 24 May 2011 Keywords: Anticipatory control Attention Older adults Gait Grasp Obstacle Hand A B S T R A C T The ability to manipulate objects deteriorates with increasing age. In the coordination of fingertip forces underlying object manipulation, older adults use excessive grip (normal) forces but maintain anticipatory force control during simple manipulations. Daily activities are often more complex and involve grasp manipulations while simultaneously performing other activities. When walking while carrying an object, young adults couple grip forces to gait-induced inertial force changes (anticipatory control). It is unclear if anticipatory control is preserved in older adults during demanding tasks. The purpose of this study was therefore to investigate aging effects on grasp control when walking and transporting an object. We included gait perturbations to vary task difficulty and step regularity associated with walking. Twelve healthy older (65–84 years) and young (20–30 years) adults transported a hand-held object during unperturbed walking, obstacle crossing and step-length changes. While older subjects employed higher grip-inertial force ratios, they showed a strong force coupling comparable to that of the young during unperturbed walking and step-length changes. During obstacle crossing the forces in the older group were less tightly coupled (grip force delays). Gait patterns were similar between groups. Our findings indicate that older adults maintain anticipatory control during regular and irregular walking. Grasp control changes in older adults only during obstacle crossing suggest that overall task demands (balance requirements, attention demands) may contribute to declines of manual dexterity in functional tasks. This highlights the need to investigate grasp control within complex tasks when aiming to understand impairments of older adults encountered in daily life. ß 2011 Elsevier B.V. All rights reserved. § This work was supported by Grant BCS-0819547 from the National Science Foundation (AMG). * Corresponding author at: 525 West 120th Street, Box 199, New York, NY 10017, USA. Tel.: +1 212 678 3326; fax: +1 212 678 3322. E-mail addresses: gd2142@columbia.edu (G. Diermayr), mcisaac@tc.edu (T.L. McIsaac), tmkamin@gmail.com (T.R. Kaminski), ag275@columbia.edu (A.M. Gordon). Contents lists available at ScienceDirect Gait & Posture jo u rn al h om ep age: ww w.els evier.c o m/lo c ate/g aitp os t 0966-6362/$ – see front matter ß 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.gaitpost.2011.05.021