Sarah - You're NUTS!

Damn girl, that is a little too much too soon! I've been working out consistently for years and never go up to 8. Granted I HATE the treadmill, but still. I usually vary my intervals depending on how I'm feeling . Sometimes I'll do 2 min jogging, 1 min running, sometimes I do 2 min running then 4 or 5 minutes jogging. You can also do intervals with the incline, not just speed. I'd definitely ease up on the speed for a while. Your poor knee! By the way, make sure your sneakers aren't worn down!