Recently the aging society is very rapid, and it has brought many problems to our society. In order to avoid these difficult situations, we focus on human standing up motion in our research because this motion is so important to our daily life that it is considered meaningful to support the motion. However, the way of human standing up is still unknown because the analysis of human motion is very difficult. Therefore, we develop integrated simulation methods to understanding the motion from human body data, such as muscle activations (EMG) and human joint torques. We carefully analyze human standing up motion based on muscle movements since muscles do move human body. Through our experiments and analysis, two important muscle coordinations (behavior primitives) are found out; one primitive has a function of generating dynamics of the motion by controlling hip, knee, and ankle and the other primitive controls posture of the body with their ankles. These behavior primitives are elucidated to be such an essential factor toward the motion that the way of standing up becomes unstable without them.