Sprinting = Pain

A lot of people begin to attempt sprint workouts when they want the sprinter body instead of the distance body. If you are unsure as to which is which....

Distance makes for a lean, toned that is usually pretty thin. Sprinting however, builds muscle, butt mass, and definition. 

In starting sprints, there is not really a way to ease into it, usually 5 100 meter sprints in rotation with slower 200s and even slower 400s will strengthen your body effectively. However, this entails stretching and pushing your muscles in ways they do not routinely stretch. This means you will be sore in the groin and quads usually. The lactic acid causing your pain is best relieved through doing cool downs after workouts and alternating easy jogging days with sprint workouts. Think fast-slow. 

However, this post mostly just stands to reassure you that pain is part of strengthening. You will get aches and pains when you begin training (no matter the distance) because your body is not used to the strain. As my high school coach once said, "Your body wants to remain still and conserve energy. Well. Your body doesn't know shit."