Musculoskeletal robot arm driven by McKibben pneumatic artificial actuators, which consists of a tubular rubber and a braided mesh sleeve, has flexibility because of the characteristics of the actuator. Although the flexibility and the complex structure make the accurate control very difficult, it can be exploited to store elastic energy, and transfer the elastic energy to kinetic energy. This suggests that the flexible structure of the musculoskeletal robot arm improves efficacy of dynamic motions such as a throwing motion. In this study, we develop a musculoskeletal robot arm inspired by a human superior limb girdle to investigate the advantage of the flexible structure.