glocktop:
I also get tired easily of scalp exercise. One way to get around that is to lie on a couch (like slouching), put your hands behind your head, and then push your head up against the couch. Then alternate and then push your head down. You can stay in these positions a longer period of time, without getting your arms tired.
I don't think that there is a correlation between body fat and laxity. However, I agree that some fat guys have a few folds on the back of their head, and that can really help with HT. However, I don't think these fat people are self-conscious or vain enough to have HT anyway.
As for body fat, unless you are an athlete or a serious body builder, I don't think it is normal to have body fat <15%.