Z- thanks. I do mix in some HIT w/o's. Not all the time, but treadmill I do variations of the, track w/o: sprint 1/4 lap, jog 3/4, sprint 1/2, jog half. Sprint 3/4, jog 1/4, sprint full lap (good luck there for me), jog lap. Mix in a cool down run or like 15 elliptical. Sometimes I do 30sec to 1...