How far should I run for sprint intervals?
Jared, it really is about what you are trying to attain. You have to think about the time of the run and the effect it is having on your body/energy systems. If you do a 10-15sec sprint at top speed you are using your body’s powerful energy molecule in Creatine and you will be developing your TYPE 2 muscle fibers. These are explosive and larger than TYPE 1 slow twitch fibers. You are even developing muscle with this short of a sprint. I would typically go with a work to rest ratio of 1:3 or 4. So, 15sec sprint/45 sec walking. This is also the best way to burn high amounts of calories. Your body really can not be at full speed in a sprint for more than about 10-15 secs. After that period you are burning carbs and are going for more endurance.
Chris Baietto, CSCS, ACE