Figure 2. Effects of a combined prevention program on incidence of hamstring injuries. Period 1 consisted of only a strength training program. In period 2, agility training was incorporated into the strength training. In period 3, flexibility training was added to strength and agility training. The number of hamstring injuries was 16 out of 116 sprinters in period 1, 12 out of 198 in period 2, and 2 out of 299 in period 3.