The triceps brachii (Latin for "three-headed" [muscle] of the arm) is the large muscle on the back of the human upper limb. It is the muscle principally responsible for extension of the elbow joint (i.e. straightening of the arm). Though a similarly-named muscle, the triceps surae, is found on the lower leg, the triceps brachii is commonly called simply the "triceps".
The three heads have the following names and origins:
Many mammals have a fourth head, the "Accessory head", which lies between the Lateral and Medial heads. In humans, the Anconeus is sometimes loosely called "the fourth head of the triceps brachii".
The triceps accounts for approximately 70 percent of the upper arm's muscle mass.
Isolation movements include cable push-downs, "skull-crushers", and arm extensions behind the back. Examples of compound elbow extension include pressing movements like the push up, bench press (flat, incline or decline), military press and dips. Using a closer grip stabilizes the arm allowing more weight to be used, so the triceps can be worked harder without assistance from the pectorals or deltoids.
Static contraction movements include pullovers, straight-arm pulldowns, and bent-over lateral raises, which are also used to build the deltoids and latissimus dorsi.
Elbow extension is important to many athletic activities. As the biceps is often worked more for aesthetic purposes, this is usually a mistake for fitness training. While it is important to maintain a balance between the biceps and triceps for postural & effective movement purposes, what the balance should be and how to measure it is a conflicted area. Pushing and pulling movements on the same plane are often used to measure this ratio.