Effect of muscle strength and movement speed on the biomechanics of rising from a chair in healthy elderly and young women

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.