Motion Analysis of Reaching Movements in a Sitting Position: Focusing on Load Change Characteristics

[Purpose] To kinematically and dynamically analyze the shift of the center of gravity, ground reaction force exerted on the buttocks to lower extremity, and thoracic to pelvic angle when executing reaching movements of the upper limb in a sitting position, and clarify their characteristics. [Participants and Methods] Twenty healthy young participants performed the task of reaching their right hand out forward in a sitting position to measure the amounts of change in the center of gravity, vertical component of the ground reaction force, and trunk and pelvic angles during the period from when adopting the initial position to when holding a target. [Results] The reaching movements were executed, with the center of gravity shifting toward the target, but the ground reaction force kept on the non-reaching buttocks. The amount of change in each angle was as follows: thoracic angle: anterior tilt, right tilt, and left rotation; pelvic angle: anteflexion, right tilt, and left rotation; and pelvic-to-thoracic relative angle: anterior tilt, right tilt, and left rotation. Thus, the results were generally similar. [Conclusion] It was suggested that healthy people execute forward-reaching movements, while maintaining a certain amount of change in the ground reaction force exerted on the non-reaching buttocks as a basis for their motor strategies.