Body Types are the different weights of characters in Brink. There are currently 3 different body types. These are Light, Medium, and Heavy body types. The heavier the body type, the more weapons are available, and vice versa, and also the climbing ability and speed of movement while in SMART.
Medium - The medium body type is the default when you first commence playing the game. With it you will have an average amount of health, and be able to use most weapons. You are able to climb anything that is up to head height.
Heavy - The heavy body type will unlock after you level up a few times. It enables you to carry all weapons, and you will have a greater amount of health. Unfortunately you move slower than the other types, and can only climb thing that are waist height.
Light - The light body type unlocks after more leveling up. You will have the least amount of health and be very limited as to which weapons you can use.However your speed will greatly increase, and you will gain the ability to do wall hops. (Allowing you to reach much higher ledges than the other body types.)