Many military trainees withdraw from basic training programs as a result of injuries sustained during training. The greatest loss of training time is attributed to overuse injuries of the lower extremities. Stretching the hamstring muscles has been shown to reduce the number of overuse injuries in this setting. Overuse injuries have been shown to be less likely to occur if hamstring flexibility is less than 30 degrees short of neutral, with the risk increasing significantly with flexibility greater than 35 degrees short of neutral. Hartig and Henderson evaluated the impact of hamstring stretching exercises on the number of overuse lower extremity injuries in military trainees.

Two groups of military trainees undergoing a 13-week basic training program were enrolled in the study. One company served as the intervention group and the other as the control group. Hamstring flexibility was measured in all trainees before and after basic training. A simple program of hamstring stretching exercises was incorporated into the trainees' normal stretching routine, once daily for the control group and four times a day for the intervention group. These exercises were taught to all trainees, drill sergeants, and the company commander, and were performed with minimal supervision. Overuse injuries, defined as stress fractures, patellofemoral knee pain, muscle strain, tendonitis, plantar fasciitis, shin splints and anterior compartment syndrome, were monitored and recorded weekly for the duration of the study.

Trainees in the intervention group increased their flexibility from a baseline of 41.7 to 34.7 degrees short of neutral, an increase of 7 degrees, while flexibility increased by only 3 degrees in the control group. The total number of overuse injuries was also significantly lower in the intervention group, resulting in less time lost from training.

The authors conclude that the number of overuse injuries can be significantly reduced with the simple intervention of hamstring stretching. Adding three additional daily sessions of hamstring stretching exercises significantly reduced the number of overuse injuries in military trainees, but the results can be applied to any population of athletes at risk for overuse injuries. However, they emphasized that these short, simple exercises were effective only if performed multiple times each day. The result, ultimately, was fewer injuries and less time lost from training.