ok, from what i understand, you subtract your age from 220 which gives you your maximum heartrate. supposedly, 65-70% is optimal for fatburning correct? that puts me at 136.5 heartrate being optimal. the problem is that's too ****ing easy. i did 40 minutes of the eliptical today keeping a heartrate of 140-145 the whole time and it felt like i didn't do a goddamn thing. i hardly sweated, didn't even begin to breathe heavy. hell, after leg's and bi's, i jumped on the eliptical with a heartrate of 170. wtf? basically, my question is will doing cardio at a higher heartrate, say 80-85% still be effective for fat burning without my body going catabolic or burning muscle?