I started running late in life (50's), but quickly became hooked; I thought it would be a good idea to start throwing in a mix of sprints (along with some distance running). I mixed up some 100's, 200's and 400's starting slow and gradually working my way up, or so I thought. On my third or fourth sprint session I did my normal warm up and started into the mixed sprints. I felt particularly good and on about my fourth go I felt like a kid and just started flying, just short of the finish BANG, felt like I got shot in the leg. I tried walking it off hoping it was something minor- a couple of days later (with no running) my wife points out that I have a long bruise on the inside of my thigh- pulled a groin muscle so bad it was bleeding internally. That marked the end of my short sprinting career
