Kinematic and electromyographic analysis of rising from a chair during a "Sit-to-Walk" task in elderly subjects: role of strength.

BACKGROUND With aging, the deterioration of the ability to rise from a chair constitutes a major source of disability and a factor contributing to the loss of autonomy. The aim of this study was to describe kinematic and electromyographic characteristics of rising from a chair during a Sit-to-Walk task and to investigate the relationships between lower limb muscle strength and Sit-to-Walk characteristics. METHODS Twenty-four healthy elderly subjects (mean age: 73.8 (6.4) years) were included. The task analyzed consisted in standing up and taking a step. Kinematic data were obtained using a 3D motion analysis software. Surface electromyography of eight lower limb muscles was recorded. Isokinetic strength of ankle plantar flexor and knee flexors and extensors was evaluated. FINDINGS The Sit-to-Walk was divided into four phases. For 19 subjects, this task can be considered as a continuum with an overlap of the phases. In comparison with the Sit-to-Stand description, the Sit-to-Walk transition phase, which combined trunk flexion and knee extension, appeared longer in order to increase the body forward transfer for gait initiation. In most cases, the tibialis anterior and peroneus longus muscles were first activated. The isokinetic strength of the knee extensors was negatively correlated with the amplitude of trunk flexion and the knee flexors/extensors torque ratio was correlated with the length of this phase. INTERPRETATION Characterization of Sit-to-Walk movement provides information about the ability to rise from a chair. In the elderly, a better knowledge of its determinants could lead to improve strategies for rehabilitation of this critical task.