Recently, the decline of children’s physical fitness has often been referred to in many fields of education. Above all, the decline of their body flexibility is a serious problem. As it is the base for delicately adjusting various physical exercise, decreasing flexibility possibly causes injuries in their daily movements.The purpose of this research was to confirm the hypothesis that body flexibility increases as body temperature rises, and also to demonstrate the increasing degree of flexibility through physical exercises. The subject of study was 67 children of 5 years old in a nursery school and a kindergarten. At the time of free activity in the morning, systemic rhythm exercise of about 20 minutes was conducted. Before and after the exercise the body temperature & flexibility were measured.As a result, the above hypothesis was proved. It also became clear that the group of the prominent increase of temperature showed more flexibility than the one of ordinary temperature. Furthermore, it was verified that both body temperature and flexibility increase in summer more than in winter.This paper concludes that it would be well advised to adopt the systemic rhythm exercise in contents of Early Childhood Education for developing their physical fitness
