Gait and Posture 8 (1998) 175–185 Effect of muscle strength and movement speed on the biomechanics of rising from a chair in healthy elderly and young women M.M. Gross a, *, P.J. Stevenson b , S.L. Charette c,d , G. Pyka c,d , R. Marcus c,d a Department of Moement Science and Institute of Gerontology, Uniersity of Michigan, Ann Arbor, MI 48109 -2214, USA b Rehabilitation Research and Deelopment Center, VA Medical Center, Palo Alto, CA 94304, USA c Geriatrics Research, Education and Clinical Center, VA Medical Center, Palo Alto, CA 94304, USA d Department of Physiology and Medicine, Stanford Uniersity, Stanford, CA, USA Received 10 March 1998; received in revised form 30 May 1998; accepted 25 July 1998 Abstract The ability to rise from a chair is an important task of daily living that is difficult for many elderly individuals to perform, and is particularly challenging when performed quickly. It is important to understand what factors limit performance of the task in older people, so that effective remedial approaches can be developed. In this study, we quantified lower-extremity muscle strength and chair-rise biomechanics in 12 young and 26 healthy elderly women during chair rise at normal and fast speeds without use of the hands. We found that hip and knee extensor torques, vertical and horizontal momentum, and vertical and horizontal ground reaction forces increased in the same way with speed for all subjects. All subjects increased their speed from normal to fast trials, but the young subjects were able to rise more quickly in the fast trials. In the normal speed trials, elderly subjects generated more trunk flexion and horizontal momentum while still in contact with the chair. Muscle activity patterns were similar for all subjects except that the elderly activated the ankle extensors earlier than the young. Although the elderly subjects were much weaker relative to body weight than the young subjects (48.5 14.1%), they were able to generate sufficient torques to perform the task. However, age-related differences suggest that chair-rise biomechanics were affected by the reduction in muscle strength, and that strength training regimens, particularly for the hip musculature, may be important to maintain chair-rise ability in the elderly. © 1998 Elsevier Science B.V. All rights reserved. Keywords: Elderly; Chair rise; Muscle strength; Movement speed; Biomechanics 1. Introduction The ability to rise from a chair is an important task of daily living, yet many elderly individuals have difficulty accomplishing the task [1]. The decreased ability to rise from a chair is important, because it can limit independence or contribute to institutionalization. The inability to rise, especially quickly, has been associ- ated with an increased risk of falling [2,3] and hip fracture [4]. Rising from a chair is a challenging task that requires both relatively large joint torques and accurate balance control. At the time of transfer from the chair, the hip torques can be larger than during other activities of daily living, such as walking and stair-climbing [5]. At the same time, the body is in a statically unstable position, with the center of mass located posterior to the base of support [6]. It is impor- tant to understand whether the balance or the strength demands of the task limit chair-rise performance in the elderly so that the most appropriate therapies can be developed. Muscle strength appears to limit the ability of elderly individuals to rise from a chair when the strength demands of the task are increased by lowering the chair height. Muscle strength typically decreases with age * Corresponding author. Tel.: +1 734 7649663; fax: +1 734 9361925; e-mail:mgross@umich.edu 0966-6362/98/$ - see front matter © 1998 Elsevier Science B.V. All rights reserved. PII S0966-6362(98)00033-2