After a few months of slowly transitioning into a mostly primal diet, I am now beginning to incorporate the primal fitness routine. I'm doing heavy lifting 2-3 times/week and have started sprinting. I don't come from an athletic background and I have always hated exercising so much to my surprise I've discovered that I am in love with sprinting, especially hill sprints! I can't get enough of 'em! That euphoric feeling and incredible energy I get after I do them make me feel pretty much invincible. I think about sprinting everyday and I want so badly to do them more than what Mark's prescribes - one session every 7-10 days. No way, I can't wait that long!

Does anyone out there do sprints more than once a week? How often can I do them without risking injury or other metabolic side effects?