Triceps brachii

Where are my Triceps?

Your Triceps are a group of muscles in the posterior compartment of your arm. In anatomy, they consist of 3 muscle bellies. Lateral, Long, and Medial Heads.

1) Lateral head - that's the most outside one, usually the smaller part of the horse shoe, and most defined.

2) Long head - it’s the inside head thats visible, usually the biggest of the 3 heads.

3) Medial head - technically this is the most inside head, but it often hidden beneath the other two heads. It can be seen however close to the elbow.


Posterior Arm

Name Breakdown: 

Triceps brachii: "tri"= meaning 3 "cep"= meaning head (this muscles has 2 heads/bellies); "brachi”=meaning on the humerus (the arm bone); and “-i”=meaning multiple bellied muscle

Triceps: There are other muscles occasionally referred to with the name ‘triceps’ in it, but the triceps brachii is by far the most commonly call just the triceps.

Why This Matters

Application for Workouts

The triceps the primary and effectively only muscle responsible for extending the arm at the elbow, and fill up the entire posterior aspect of the upper arm.

Similar to how the Biceps brachii flexes the elbow and draws the forearm closer to the arm, the Triceps brachii extend the elbow and draw the forearm away from the arm. One of the 3 heads of the triceps crosses the shoulder and inserts into the scapula. For this reason, the triceps has some function in adducting and extending the arm.

On an Arm day:

  • Long Head: It is impossible to isolate either of the heads of the triceps, however we can try to emphasize one more than the other. The long head can emphasized by taking advantage of the fact it crosses the shoulder joint. This means doing overhead movements. it is also activated inadvertently during some back exercises due to its ability to help extend the shoulder joint.

  • Lateral Head & Medial Head: The best way to emphasize the lateral and medial heads is to de-emphasize the long head. In order to remove the effort of the long head, you want to perform movements with your arms by your sides. There is some debate on whether you can actually isolate the lateral head from the medial head, but those who believe you can say that utilizing an over hand grip is more effective for targeting the lateral head, while an under hand grip is more effective at targeting the medial head.

Emphasis on Bodybuilding

Triceps are an important muscle for bodybuilding because they provide width to the arms on the sides, and depth when viewed from the side. They provide balance to the arm against the size of the biceps brachii and assist to accentuate the deltoid, especially the middle and posterior heads of the deltoid. In well developed arms have more of their volume taken up by the triceps than the biceps, despite common public belief that the biceps are larger.

For bikini competitors, the triceps appear primarily in the transition and back poses. This is especially true if you look back at the judges over your shoulder, because you are drawing attention to your face, and by proximity to your shoulder. Your rear delt can really pop if you also have a well defined triceps brachii. If you are in a higher level than bikini, or a male competitor, it becomes even more important to have large triceps, and not just well defined ones.

These muscles can be difficult for some to isolate, and for others to develop symmetrically between the lateral and long heads. Selection of triceps exercises should be in line with your goals to growing each of the different heads, as it can take more time and effort to develop the triceps symmetrically than other muscles if they become out of symmetry.

It is important to maintain strong, healthy triceps because many people tend to over work their biceps, which can shorten/tighten and limit the function of the triceps.


1) Triceps brachii Long-Head: infraglenoid tubercle of the scapula

The insertion is just underneath the head of the humerus in the shoulder joint (deep in the armpit).

2) Triceps brachii Lateral-Head: lateral portion of the humerus shaft

3) Triceps brachii Medial-Head: medial portion of the humerus shaft


1) All 3 Heads: Olecranon Process of the Ulna


1) Triceps brachii All 3 heads: 

The primary action of the Triceps brachii is to straighten the elbow. The anatomical term for this is Extension of the elbow, or Extension of the forearem AT the elbow. A good example of this movement is the Cable Triceps Push downs.

2) Triceps brachii Long-Head only:

The long head can be emphasized in certain triceps specific movements such as the over head triceps extension, or skull crusher.

The secondary action of this specific head is to extend or adduct the arm relative to the shoulder. It becomes an accessory muscle in movements such as rear deltoid flies, or lat pull downs.


When a muscle acts as antagonist, it is trying to resist the action of a different muscle. Since the triceps has 2 different motions, it has 2 different opposing directions as well. The major antagonists are the Biceps brachii, brachialis, and coracobrachialis.

  1. The Biceps brachii and the Brachialis both flex the elbow, therefore opposing the elbow extension action of the triceps.

  2. The Coracobrachialis helps to flex the arm, as does many other muscles, therefore opposing the arm extension action of the triceps.

Nerve Supply:

The Triceps are innervated by the Radial nerve. This nerve also innervates the extensors on the back of the forearm, including the brachioradialis, and the extensors of the fingers. The Radial nerve goes across your armpit into the back of your arm.

This nerve comes from the Posterior Cord of the Brachial Plexus. The Brachial Plexus is the main set of nerves that innervate the arms, chest and upper back. The Posterior cord is generally involved in muscles that extend anything in the arm, such as the lats, triceps, deltoid, teres major and minor, and forearm/finger extensors.

Blood Supply:

The Triceps are primarily supplied by the Deep Brachial Artery. This is is a branch of the Brachial Artery which supplies the the arm. The Brachial artery does the front of the arm, and the enitrity of the forearm, while the deep brachial just does the back of the upper arm (triceps and related skin, bone, etc).

Blood Flow: Heart -> Aorta -> Subclavian a. -> Axillary a. -> Brachial a. -> Deep Brachial a.

Example Exercise Videos to Work this Muscle