Characteristics of the stand-to-sit motion in healthy older women : Evaluation of sitting impact by measurement of ground reaction forces

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Objectives : The aims of this study were to examine the biomechanics of StandTS movements in older adults and to identify their optimal StandTS motion by measuring sitting impact forces. Methods : Healthy older women (n = 17) and healthy young women (n = 18) were asked to perform SitTS and StandTS motions at a natural speed using a chair. We measured the ground reaction forces from the participants’ feet and the chair, the angle of the trunk and ankle, vertical velocity, and postural muscle activities using a force plate, motion analyzer, and electromyography, respectively. Results : Sitting impact force was significantly greater in the older women than in the young women during the StandTS motion. There was a significant difference between the trunk angle and the ankle angle during the StandTS motion and sitting impact force had a significant negative correlation with the ankle joint motion in the older women. Conclusions : The ankle joint strategy was characterized by body sway resembling a single-segment-inverted pendulum and suggests that this response is less developed in the older adult. These results indicate that the ankle joint strategy may be an important factor involved in the sitting impact force. J. Med. Invest. 69 : 278-286, August, 2022