Weight Training

Could do with some help here. I've got two characters, one's stronger than the other will ever be, but the weaker character is in better shape. So is saying that the character in better shape did three times as many circuits with weights that are only half as heavy a good way of getting that across? (The weaker character is only sixten, the stronger character is twenty-five and a bit stronger than a human of his build and general condition really should be)