Transfer strategies used to rise from a chair in normal and low back pain subjects.

The mechanics of rising from a chair are analysed in two groups of male subjects including five normal subjects and five chronic non-specific, low back pain subjects. Chair height, foot placement and arm position were controlled while force plate, video and electromyographic data were collected. The task was broken into three phases: initiation, chair unloading, and ascending. Moment and power analyses of the ascending phase showed two different strategies were used among the normal subjects. A 'knee strategy', comprising higher knee muscle moments, propelled the body into the standing posture while keeping the trunk relatively vertical; a 'hip-trunk strategy' flexed the trunk farther forward, decreasing the knee moments, but at the same time increasing the moments at the hip and low back. The low back pain subjects used a modified strategy that distributed the moments and power more evenly throughout the lower limb and low back.