The purpose of this study was to examine factors related to the occurrence of enthesis pain by long-term longitudinal investigation and measurement in junior high school soccer players, while intervening for its prevention. The subjects were 107 male junior high school soccer club members. The presence or absence of enthesis pain, the height growth velocity, muscle tightness, and alignment were longitudinally investigated, and stretching was instructed periodically. The time of enthesis pain occurrence was consistent with phase II of the height growth velocity curve in many cases. On comparison between before and after the appearance/disappearance of enthesis pain, no association was noted between the muscle tightness and occurrence of enthesis pain. But, on comparison of changes with time in muscle tightness, the tightness of the right quadriceps significantly increased, being useful for the prediction of enthesis pain. A significant increase in the Q-angle was also noted when enthesis pain appeared. Furthermore, the tightness of the bilateral iliopsoas, hamstrings, hip adductors, and gastrocnemius had significantly improved on the final measurement, showing that instruction in stretching was effective. This study showed the necessity of the long-term longitudinal evaluation of muscle tightness, suggesting that there is a possibility of intervention for prevention, as well as physical therapy for sporting injuries in the growth period.