The triceps brachii to use it's full Latin name means three-headed muscle and makes up 2/3 of the muscle mass in the arm.
LOCATION OF THE TRICEPS
The triceps are located on the under side of the upper arm and join together at the elbow.
FUNCTION OF THE TRICEPS
The function of the triceps is mainly for extending the elbow joint in other words straightening of the arm. Also when using small movements with the hand the triceps plays a part by controlling the elbow.
The triceps makes up approximately 70% of the arms actual size, so if you want to fill out those t-shirt sleeves the triceps are the muscles you want to be hitting!