The purpose of this study was to determine the effectiveness of insole for flexible flat foot subjects. In this study, all tests were conducted with and without insole during stance phase of two-legged vertical jumping on a force plate for heading a ball. Fifteen flexible flat foot subjects were randomly assigned to the study and fifteen normal foot subjects of male sex voluntarily participated in this study. One type of removable insole was used for flexible flat foot test subjects. All the subjects were instructed land on the force platform and make their maximal convenient two-legged vertical jump to head a suspended ball. The mean of three acceptable jumps were recorded for reference group and test group for further analysis of kinetics of jump. The results demonstrated that the use of the insole could not have a significant effect on parameters regarding sagittal and mediolateral directions in the normal and flexible flat foot subjects (p≥0.05 respectively). Moreover, findings of ground reaction forces related to vertical direction for maximum force due to take off and stance duration revealed significant differences between the normal foot and flexible flat foot subjects without insole (p< 0.05 respectively) and insignificant differences between the normal foot and flexible flat foot subjects with insole adoption (p≥ 0.05 respectively).
