Gait and Posture 19 (2004) 50–57 Muscle activity during gait initiation in normal elderly people J. Mickelborough a,* , M.L. van der Linden b , R.C. Tallis c , A.R. Ennos d a Centre for Rehabilitation and Human Performance Research, Brian Blatchford Building, The University of Salford, Frederick Road, Salford M6 6PU, UK b Anderson Gait Analysis Laboratory, Rehabilitation Engineering Services, Princess Margaret Rose Orthopaedic Hospital, Edinburgh EH10 7ED, UK c Division of Geriatric Medicine, The University of Manchester, Manchester, UK d School of Biological Sciences, The University of Manchester, Manchester, UK Received 4 October 2001; received in revised form 20 December 2002; accepted 27 January 2003 Abstract The purpose of this study was to describe the patterns of phasic muscle during gait initiation in normal elderly people. Bilateral surface EMG recordings were made of tibialis anterior, medial gastrocnemius and gluteus medius activity throughout gait initiation in 21 subjects. A variable expression of the onset muscle pattern is shown, with a tendency for muscle activity to be more variable in the preparatory phase. These results provide a baseline of normal gait initiation muscle activity against which to compare that of patients with gait initiation and balance difficulties. © 2003 Elsevier B.V. All rights reserved. Keywords: Gait initiation; EMG; Elderly people 1. Introduction Gait initiation is normally a stereotypical and unconsid- ered transition from stance into walking, with a consistent pattern of muscle activity [1,2]. In the absence of external forces, muscle activity is required to initiate gait from a standstill. An appropriate horizontal ground reaction force (GRF) component must be generated to accelerate the cen- tre of mass (COM) forwards and towards the stance side. To achieve this, co-coordinated muscle activity initially moves the centre of pressure (COP) posterolaterally towards the swing leg (the first leg to leave the ground) side of the base of support (BOS), as shown in Fig. 1. In young adults, the predominant pattern of muscle activ- ity to produce the posterior element of COP movement is a bilateral inhibition of tonic gastrocnemius/soleus activity, closely followed by a bilateral burst of phasic tibialis anterior activity [3,1]. The combined effect of this muscle activity is to produce an external dorsiflexion moment at the ankles tending to rotate the body forwards over the feet. The hip abductors contribute to the control of frontal plane motion of the COM and the lateral loading/unloading mechanism during stance phase [4,5], and gait [6]. During gait initiation, * Corresponding author. Tel.: +44-161-295-3487; fax: +44-161-295-2302. E-mail address: j.mickelborough@salford.ac.uk (J. Mickelborough). anticipatory postural adjustments in the frontal plane shift the COP towards the swing foot, accelerating the COM to- wards the stance side (the last leg to leave the ground in gait initiation), allowing the swing foot to be lifted [7]. Both the hip adductors and abductors contribute to this movement [8]. Gait initiation is divided into a preparatory and a step- ping phase each of similar duration. The preparatory phase lasts from onset until the toe-off of the swing foot (SW TO) and is divided into two sub-phases, a release phase and an unloading phase [9,10]. During the release phase the COP is moved posterolaterally towards the swing foot, increasing the horizontal GRF components that accelerate the COM in the opposite direction [11]. This release phase lasts until the furthest point of posterolateral COP movement (maxCOP), when the COP abruptly changes direction (Fig. 1), mark- ing the start of the unloading phase. During the unloading phase, the COP is moved rapidly across to the stance foot, unloading the swing foot for toe-off. Swing leg toe-off marks the start of the stepping phase of gait initiation, which is sub-divided into single and double support phases (SSP and DSP). The SSP lasts from SW TO until initial contact of the swinging foot (SW IC), with DSP lasting from SW IC until toe-off of the original stance foot. There are few data available in the literature describing muscle activity during gait initiation in either young adults or the elderly, and no comprehensive data available describing the phasic activity of these muscles throughout gait initiation 0966-6362/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0966-6362(03)00016-X