Sit-to-stand task is an important and kinetically challenging task for stroke patients. From the muscular strength perspective, it is well known that a large knee extension moment is required to lift the thigh. Energy flow from trunk and shank to lift the thigh has already been shown. Therefore, kinematic coordination is also necessary for the sit-to-stand task.

In this study, sagittal movement onset of each segment of the body (thorax, pelvis, thigh, shank), hip joint center (HJC), and knee joint center (KJC) were compared between young (YOUNG, three people) and elderly (ELDERLY, four), and stroke patients (STROKE, three) for sit-to-stand task. We used VICON Nexus 2.5 (VICON corp.) to measure the body kinematics.

Fig. 1 presents temporal order of movement onset of the body parts. The time difference within 0.005 [sec] is regarded as simultaneous, and a single quotation is added on number. The group difference existed between YOUNG and ELDERLY (e.g. mean thigh-shank was 0.13, −0.07 [s], respectively; P=0.01). ELDERLY and STROKE (two-thirds people, paretic side) had similar timing.

In YOUNG, there is a possibility that trunk flexion lead to the translation of HJC and KJC, so that tilted the shank forward. Also, these results were consistent with a previous study that movement (work) of the trunk and shank contributes to lift the thigh. ELDERLY and some STROKE were different from this order. They may have used the movement strategy inferior in terms of energy cost, because the movement trajectory of healthy adults is controlled so that the torque of each joint is minimized. Although movement coordination is difficult to evaluate, we could provide basic knowledge from the standpoint of kinematics.