INTERSEGMENTAL DYNAMICS OF STANDING FROM SITTING

Objective. To compare the magnitude of muscle moments acting on either end of body segments with other motion-dependent and gravitational mo ments during the task of standing up. Design. A mathematical model whi ch partitions moment components was developed and applied and descript ive analysis of the resultant data conducted. Background. It has been hypothesized that segmental interactions may be exploited during the t ask of standing up from sitting to lessen demands for the production o f large muscle forces. There has been no investigation of the relative sizes of these interactions nor of their impact on the task. Method. Kinematic data obtained from six healthy male subjects were used as in puts to a 'top-down' dynamic model. Each total segmental moment was pa rtitioned into a net muscle component as well as gravitational and mot ion-dependent components. Results. The model successfully predicted bo th muscle moments determined by the 'ground-up' inverse dynamics appro ach and also ground reaction forces measured with a force platform. Mo tion-dependent moments were consistently small compared with muscle an d gravitational moments. Conclusion. Segmental motion during standing up is controlled almost entirely by gravitational moments and the dire ct action of muscles which span either end of the segment. Motion-depe ndent moments do not significantly reduce the muscle moments required to stand up. Relevance Knowledge and understanding of the mechanical d emands on the body during rising from sitting to standing are importan t in identifying critical elements for successful performance. Such in formation may also provide a basis for the development or refinement o f strategies to retrain the movement following injury or disease. (C) 1997 Elsevier Science Ltd.