Endurance

This is basically how fit a character is. There is a big difference between being strong and being fit. A muscular person who is not fit could lift something very heavy, but will tire easily and could not run a marathon. Meanwhile, someone who does not look very strong, but is fit, could keep on running long after the unfit person has become exhausted. This comes into play by reducing the amount of damage sustained in combat, and when testing to see if one can continue doing something strenuous like treading water.

Examples of highly fit people include marathon runners, Greek heroes, soccer players, and masochists.