Triceps brachii

Function

Three heads, one tendon

The triceps brachii is a big, thick muscle at the back of the upper arm, often shaped like a horseshoe¹. No other muscle runs along the back of the humerus (upper arm bone)³. It has three heads: a long head, a lateral (outer) head and a medial (inner) head¹. Together they form a spindle-shaped muscle that crosses both the shoulder and the elbow³.

The heads start in different places³:

• The long head starts on the infraglenoid tubercle, a small bump on the scapula (shoulder blade) just below the shoulder socket¹.
• The lateral head starts on the outer side of the humerus³.
• The medial head starts on the back and inner side of the humerus³.

One dissection study used 64 specimens from 36 cadavers (bodies donated for study)⁷. In it, the long head was fused with the joint capsule and attached directly to the labrum⁷. The joint capsule is the sleeve of tough tissue that encloses a joint. The labrum is a rim of tough tissue around the edge of a joint socket.

The three heads join in one tendon on the upper olecranon, the bony point of the elbow on the ulna (one of the two forearm bones)¹. The medial head has its own tendon, which lies deeper than the tendon of the other two heads and is separate at first³. The distal triceps tendon page covers this attachment in detail.

What it moves

The triceps’ main job is to extend (straighten) the elbow¹. The anconeus, a small muscle at the back of the elbow, adds a little to this work³. One review describes the medial head as working in every kind of elbow straightening³. By that account, the long and lateral heads join in mainly when the elbow straightens against resistance³.

Of the three heads, only the long head crosses two joints². Through it, the triceps helps with shoulder extension, moving the arm backward³. So do the latissimus dorsi (a broad back muscle), the back of the deltoid (the rounded muscle that caps the shoulder), and teres major (a thick shoulder muscle)³. The triceps also plays a part in adduction, bringing the arm toward the body, though other muscles matter more for it³. When the arm is raised to the side, the long head helps hold the top of the humerus from slipping downward³.

Of the three heads, only the long head crosses two joints.

In 18 people whose triceps was electrically stimulated, its pull backward at the shoulder rose significantly as the arm was raised from 0° to 80°⁸. A review by the same authors adds that it fell slightly beyond 80°³.

Size, fibres and leverage

In 10 arm specimens, the triceps had the largest physiological cross-sectional area of the major elbow muscles, at 14.9 cm²⁹. That is a measure of size taken straight across all of a muscle’s fibres. The triceps is made mostly of type 2 fibres, which contract fast¹⁰.

A muscle’s moment arm is its leverage: how far its line of pull sits from the joint it turns. In MRI scans (which show soft tissue in detail) of 18 people, the triceps’ moment arm grew as the elbow straightened¹¹. It went from 1.74 cm with the elbow bent to 110° to 2.39 cm at 30°¹¹. A review reports that in 10 cadaver arms, the front-to-back depth of the ulna explained over 60% of the spread in peak moment arm³.

Its nerves and blood supply

The triceps is supplied mainly by the radial nerve, which comes from the brachial plexus (the network of nerves that serves the arm)¹². In 30 arms dissected from 15 cadavers, the radial nerve always gave at least four branches to the triceps¹³. One went to the long head, one to the lateral head and two to the medial head¹³.

A narrative review (a summary written without a set search method) pooled 15 studies of 336 specimens¹². In 55, the axillary nerve (the nerve that makes the deltoid contract) supplied the long head¹². The radial nerve was still the main source¹². Across 11 studies of 318 specimens, the medial head got ulnar nerve branches in 64¹². The ulnar nerve runs past the inner side of the elbow to the little-finger side of the hand.

Blood reaches the triceps through the profunda brachii artery (deep artery of the arm)¹⁴. It runs between the lateral and medial heads with the radial nerve, and gives branches to the muscles and the humerus¹⁴.

Breakdown

Where the triceps can tear

One case report lists triceps tears and avulsions at the bone, in the tendon, where muscle meets tendon, and in the muscle belly⁴. An avulsion is a tear in which a tendon pulls away from the bone it attaches to. It calls these injuries uncommon⁴.

It says tears inside the muscle belly are rarer than tendon tears⁴. Its literature review found only 9 earlier reported cases⁴. The authors describe these tears as usually seen in young, active people who play sports; 7 of the 9 were male⁴. Most followed a direct blow while the muscle was contracting during sport; only 2 involved indirect force⁴.

The distal triceps tendon page covers tendon tears in detail. A systematic review gathers all the research on a question. In pooled results from one, men outnumbered women 11 to 1 among tendon tears¹⁵. Among athletes with repaired tears in another review, weightlifting was the most common activity, followed by American football¹⁶. In resistance training, a review reports these tears mainly while lowering the bar in bench or overhead pressing, as the triceps lengthens¹⁶.

Snapping triceps

In snapping triceps syndrome, part of the lower triceps slides over the medial epicondyle (the inner bony bump of the elbow) as the elbow bends¹⁸. It makes a snap that may or may not hurt¹⁸. A literature review of 24 studies describes it as rare but often misdiagnosed¹⁸. Of 64 patients pooled in that review, 90.6% also had an unstable ulnar nerve, and 64.1% had ulnar nerve symptoms¹⁸.

The long head and the shoulder

The long head has been seen affected when the axillary nerve is injured¹². The authors of the dissection study above proposed that the long head could be indirectly linked to posterior (backward) shoulder instability⁷. They based this on its ties to the capsule and labrum⁷.

Recovery

How it grows with training

In eleven men who trained the triceps for 12 weeks, its largest cross-sectional area (the size of a slice across the muscle) rose 33.6%¹⁹. Its moment arm rose 5.5%, less than muscle size alone predicted, and the depth of the olecranon did not change¹⁹. In 18 people imaged with MRI, a larger triceps went with a longer moment arm at every elbow angle measured¹¹.

After 12 weeks of elbow extensor training, the lower region grew significantly less than the middle and upper regions²⁰. This matched lower activity in the lower region during a single session²⁰. In twelve young men training with a multijoint exercise for 12 weeks, the middle regions grew significantly more than the uppermost region²¹. That matched where the muscle was most active in the first session²¹.

Arm overhead or at the side

The long head is stretched further with the arm overhead than with the arm at the side⁵. In one study, 21 adults trained one arm with overhead cable elbow extensions and the other with the arm at the side, for 12 weeks⁵. MRI measured the growth in muscle volume⁵:

Part of the triceps	Overhead arm	Arm at the side
Long head	+28.5%5	+19.6%5
Lateral and medial heads	+14.6%5	+10.5%5
Whole triceps	+19.9%5	+13.9%5

The overhead arm always lifted 34–39% less weight, yet strength rose by a similar amount in both arms⁵. A review calls the extra growth in the lateral and medial heads unexpected, because those heads cross only the elbow⁶. It suggests factors other than muscle length may be involved⁶.

The evidence does not all agree⁶. A second study making the same comparison found no difference in long head growth⁶. That review suggests the gap may come from how muscle was measured, study length (12 against 6 weeks), or how the exercise was set up⁶.

After a tear in the muscle

A case report notes that earlier reports described good or excellent overall results for triceps muscle-belly tears managed without surgery⁴. Some reports noted a slight loss of straightening power and endurance⁴. The case itself was a 22-year-old college water polo player with tears in the long and lateral heads⁴. Managed without surgery, he returned to competition 7 months after the injury⁴.

Connections

The biceps brachii

The biceps brachii, at the front of the arm, and the triceps, at the back, work as an opposing pair²². The biceps bends the forearm and the triceps straightens it²². In 10 arm specimens, the triceps’ long head changed length by 28% of its best working length across elbow motion⁹. The biceps’ long head changed by 56%, because its moment arm was larger (4.7 cm against 2.3 cm)⁹.

Fascicles are bundles of muscle fibres lying side by side. In an ultrasound (sound-wave scan) study of 11 healthy people, the triceps’ lateral head had much shorter fascicles than the biceps’ long head²³.

The shoulder muscles

At the shoulder, the long head helps move the arm back alongside the latissimus dorsi and the back of the deltoid³. At the elbow, one anatomy study notes the three heads have long been described as joining in a single attachment on the olecranon²⁴. The distal triceps tendon page covers it.

Exercises that load it

Studies that record muscle activity with EMG describe how common exercises use the triceps^2,25,26. Related exercise pages: triceps extension, bench press and overhead press^5,25,27.

Exercise	What studies found
Triceps extension	In 10 healthy people, the long head made most modelled force with the arm down; the medial head did with it raised 90° or more2
Triceps extension	In 25 people doing pushdowns to failure, EMG suggested the three heads did not act together as one28
Bench press	A systematic review of 14 EMG studies found triceps and pectoralis major (the large chest muscle) activity similar, and both above the front deltoid25
Bench press	In 28 men lifting their 6-repetition maximum (heaviest load for six lifts), triceps activity was lower with a wide grip than medium or narrow29
Overhead press	In 15 healthy men pressing standing, triceps activity was about 39% greater with a barbell than with dumbbells26
Push-up	In 20 young men, triceps activity was significantly higher than pectoralis major activity in standard, diamond and wide push-ups30
Dip	In 13 experienced men, 11 of whom did the ring dip, peak triceps EMG was 0.83 mV on a bench, 1.04 mV on bars and 1.05 mV on rings31

Sources

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5. Maeo S, Wu Y, Huang M, Sakurai H, Kusagawa Y, Sugiyama T, Kanehisa H, Isaka T (2023). Triceps brachii hypertrophy is substantially greater after elbow extension training performed in the overhead versus neutral arm position.. European Journal of Sport Science. doi:10.1080/17461391.2022.2100279 PMID 35819335
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15. Shuttlewood K, Beazley J, Smith CD (2017). Distal triceps injuries (including snapping triceps): A systematic review of the literature.. World Journal of Orthopedics. doi:10.5312/wjo.v8.i6.507 PMID 28660143
16. Vandenberg CJ, Touhey DC, Brophy RH, Smith MV, Knapik DM (2026). Distal triceps tendon rupture repair results in high return to sport rates for amateur and professional athletes: a systematic review.. JSES Reviews, Reports, and Techniques. doi:10.1016/j.xrrt.2026.100694 PMID 41847163
17. Mangano T, Cerruti P, Repetto I, Trentini R, Giovale M, Franchin F (2015). Chronic Tendonopathy as a Unique Cause of Non Traumatic Triceps Tendon Rupture in a (Risk Factors Free) Bodybuilder: A Case Report.. Journal of Orthopaedic Case Reports. PMID 27299023
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24. Barco R, Sánchez P, Morrey ME, Morrey BF, Sánchez-Sotelo J (2017). The distal triceps tendon insertional anatomy-implications for surgery.. JSES Open Access. doi:10.1016/j.jses.2017.05.002 PMID 30675548
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28. Hussain J, Sundaraj K, Subramaniam ID, Lam CK (2020). Muscle Fatigue in the Three Heads of Triceps Brachii During Intensity and Speed Variations of Triceps Push-Down Exercise.. Frontiers in Physiology. doi:10.3389/fphys.2020.00112 PMID 32153422
29. Saeterbakken AH, Stien N, Pedersen H, Solstad TEJ, Cumming KT, Andersen V (2021). The Effect of Grip Width on Muscle Strength and Electromyographic Activity in Bench Press among Novice- and Resistance-Trained Men.. International Journal of Environmental Research and Public Health. doi:10.3390/ijerph18126444 PMID 34198674
30. Intziegianni K, Katsamis E, Michaelides M, Parpa K (2026). Electromyographic Activation of the Pectoralis Major and Triceps Brachii Muscles During Standard, Diamond, and Wide Hand Position Push-Ups.. Muscles. doi:10.3390/muscles5010018 PMID 41892990
31. McKenzie A, Crowley-McHattan Z, Meir R, Whitting J, Volschenk W (2022). Bench, Bar, and Ring Dips: Do Kinematics and Muscle Activity Differ?. International Journal of Environmental Research and Public Health. doi:10.3390/ijerph192013211 PMID 36293792

Every source the library cites

Changes

• October 8, 2026 Revised to report sources added after their published corrections were read
• September 29, 2026 First published.