If humans hadn't lost their tails and today we had fully prehensile tails as long as 1/2 our body and stronger than an arm, how would the tail of a bodybuilder or just a buff person look? Would tail muscles be as visible as the trapezium or the abdominal and change completely the appearance and morphology of the body, or would they be non-visible?
And most importantly, how would the back of a human look?
By fully prehensile I mean the tail can be controlled to lift, move or hold still weights as heavy as the person's own body (just like monkeys do), and it can also do involuntary motions to express emotions just like our faces do. Tails are used as third limbs in daily life.