Control of lateral weight-transfer initiation during sitting

Whereas many researchers have examined the transition from quiet posture to dynamic state, study of the initiation of lateral weight-transfer during sitting has only begun recently. This action is included in many tasks performed in our daily living, i.e., reaching, dressing, looking backwards, lying down, and shuffling the buttocks. The present study was designed to describe lateral weight-transfer movements of healthy adults, kinematically and kinetically, and to clarify the strategies and speed dependency of lateral weight-transfer initiation during sitting. Seven healthy Japanese male students without orthopaedic or neurological disorders participated. Their lateral weight-transfer movements were measured during sitting, using two force platforms and a 3-dimensional analysis system. Analysis showed that there appear to be two strategies for the initiation of the task: one is the lateral bending of trunk toward the weight-transfer side, and the other is a coordinated reciprocal leg action of both legs. A combination of these strategies is used in a trade-off fashion during natural motions. These results are clinically important for the assessment and therapy of patients with sitting problems.