The purpose of this intervention study was to prove that increasing flexibility of the hamstring musculotendinous unit would decrease the number of lower extremity overuse injuries that occur in military infantry basic trainees. Two different companies going through basic training at the same time were used. Hamstring flexibility was checked at the beginning and at the end of the 13-week infantry basic training course. The control company (N = 148) proceeded through normal basic training. The intervention company (N = 150) followed the same program but added three hamstring stretching sessions to their already scheduled fitness program. All subsequent lower extremity overuse injuries were recorded through the troop medical clinic. Hamstring flexibility increased significantly in the intervention group compared with the control group. The number of injuries was also significantly lower in the intervention group. Forty-three injuries occurred in the control group for an incidence rate of 29.1%, compared with 25 injuries in the intervention group for an incidence rate of 16.7%. Thus, in this study, the number of lower extremity overuse injuries was significantly lower infantry basic trainees with increased hamstring flexibility.