You are stronger than your size hints at. You are not (much) larger than others, but you have a visibly athletic build. The trait is used whenever raw strength is used or of use, such as lifting things, tug-of-war, climbing, grappling etc. It increases your encumbrance limit by 1 kg per step of this trait. If you have +2, your encumbrance limit is 14 kg instead of 12 kg. The trait also applies to most melee attacks, wrestling and brawling. It has no influence on ranged combat. It only applies to the Lethality of your attacks, not your ability to hit. So apply the bonus Lethality after counting Excess.
Cannot be taken if you have Weak.