80%... I don't know about that.... if you just want to tone up then you want to do about 9-10 reps on weights which are medium resistance to you. The muscle will only grow once you actually 'tear' it apart and then it recovers, you have to sort of almost injure yourself. If you want to add lots of muscle then you want to be doing low reps.. as low as 3 or 4, at maximum resistance.