Those of you who do it, please list your routines and also how often a week is optimal to do it. Hills, sand, treadmill, stairmaster, elliptical, rowing, bike, rope whatever. Also, would a spinning class qualify as interval training? For those of you who do interval training regularly, do you typically do this after a workout, before, or separately? Those of you who use heart rate monitors, what's the target %'s etc.