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:
- The "Long head": infraglenoid tubercle of the scapula
- The "Lateral head": posterior shaft of the humerus, lateral and superior to the radial (spiral) groove.
- The "Medial head": posterior shaft of the humerus, medial and inferior to the radial (spiral) groove.
The fibers converge to a single tendon to insert onto the olecranon process of the ulna (though some research indicates that there may be more than one tendon.)
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 is an extensor muscle of the elbow joint, and is an antagonist of the biceps and brachialis muscles. It can also fixate the elbow joint when the forearm and hand are used for fine movements, e.g., when writing.
The triceps accounts for approximately 50 percent of the upper arm's muscle mass.
The triceps can be worked through either isolation or compound elbow extension movements, and can contract statically to keep the arm straightened against resistance.
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. A closer grip targets the triceps more than wider grip movements.
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.
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