Hip kneepads, specially designed to relieve knee pressure. Also, if you are heavy, don't squat at first, or aerobic for a while, and then add strength when it is not too heavy (that is, squat, bench press and so on). I don't know how fat you mean by overweight. If you are just a little fatter, you can run and jump rope. If you are really fat, you can swim or ride a bike.