The purpose of the present study was to investigate the relationship between muscle strain and the running form at start dash. Twelve male sprinters were divided into two groups, an injured group (N=7) and an uninjured group (N=5), according to their history of previous hamstring muscles strain. They were filmed at the 1st step and the 5th step after starting with crouching style by means of a 16mm motion picture camera. Ground reaction forces were measured with a Kistler force platform. Selected kinematic and kinetic variables, such as joint angles, muscle length of hamstrings and muscle torques of the lower limb, were computed. The results were as follows; 1) The injured group tended to swing the lower leg more forward and the thigh backward less quickly before touchdown than the uninjured group. They also tended to show a greater thigh angle of the support leg at touchdown and to flex the support leg at the 5th step more than the uninjured group. 2) The injured group showed a significantly larger hip extensors torque than the uninjured group during the first half of the support phase for the 5th step. 3) The injured group showed greater shortening velocity of hamstrings during the first half of the support phase for the 5th step. The results suggest that larger hip extensors torque and greater shortening velocity of hamstrings during the first half of the support phase will be factors of the occurrence of muslce strain during start dash. These factors might be due to the start dash form such as contacting with a greater thigh angle of the support leg and flexing the support leg during support phase for the 5th step. This suggests that there exist the running form and the stage of sprinting where hamstring muscles strain is susceptible to occur.