bro, you have to understand that when you are dieting like that and trying to lose weight that it doesn't matter what your running, your going to lose some muscle... 1500 calories is so little... if your not feeding muscles enough, they will diminish... do you know the absolute hell that i have to go through to put on weight and drop body fat... its an everyday boot camp, with no breaks and no cheating... so your going to have to decide what you want to do... s4 is for leaning out and muscle hardening...