Everytime I attempt to do sprints I end up tweaking a hammy. I do extensive static and dynamic stretching before hand and I am in very good shape. I'm only 20 years old and I played running back in high school so sprinting should not be a problem for me. Over the past couple of months everytime I do sprints it seems that I will tweak or pull my left or right hamstring when I am in full stride on my third or fourth sprint. Sometimes I pull them worse then other times but usually I can still jog or run lightly after. It is only when I am in full stride they tend to get messed up. It's starting to really frustrate me. Does anybody have any ideas why this may be happening? I never had this problem before in highschool.