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Investigation of the Factors of Standing Instability in Elderly People after Rising Quickly from a Chair

[Purpose] This study investigated the factors of standing instability in elderly people after standing up quickly. [Participants and Methods] The participants were 15 healthy elderly men. Using a three-dimensional motion analysis system, we measured the movement of rising from a chair as quickly as possible and the standing posture after standing up. The effective value of the center of gravity in the anterior and posterior directions was used as the index of standing instability after standing up. We examined the correlation between the effective value and items of the kinematic data in the standing up motion. [Results] A negative correlation was shown between the effective value and the timing of the left hip extension moment, and a positive correlation was shown with the maximum value of the left knee joint moment. [Conclusion] The results suggest that a factor of standing instability after standing up quickly is eccentric control of the hip joint in bending of the trunk after seat off, and that standing instability may be affected by the strength of the knee extensor muscles related to hip joint control.