Triceps Brachii Anatomy: Lateral, Long and Medial Heads Explained

Triceps brachii anatomy is simple to describe and easy to overcomplicate. There are three heads, the long, lateral and medial, and all of them straighten the elbow. Only the long head also crosses the shoulder, and that is the one detail that should change how you train.

This page is the anatomy map for the back of the upper arm. For the full arm picture, including biceps, brachialis and forearms, see our complete arm and forearm training guide. Here we stay on the triceps: what each head is, what the research says about them, and what “horseshoe triceps” really means.

What are the three heads of the triceps brachii?

The name says it: tri-ceps, three heads, one muscle. They all merge into a single tendon that attaches at the point of the elbow, and their job is to straighten it.

• Long head. Starts on the shoulder blade (scapula), so it crosses both the shoulder and the elbow. This is the biarticular (two-joint) head. It forms most of the underside of your upper arm.
• Lateral head. Starts on the back of the upper arm bone and sits on the outer side. It forms the outer part of the “sweep” you see from behind.
• Medial head. Lies deeper, underneath the other two. It only crosses the elbow, like the lateral head.

That origin and insertion layout is standard textbook anatomy. The interesting question for a lifter is not where the heads sit, but whether they behave differently when you train.

Does the shoulder position change what the triceps do?

Yes, but mainly for one head. Because the long head crosses the shoulder, raising your arm overhead stretches it before you bend the elbow at all. The lateral and medial heads do not care where the shoulder is, since neither crosses it.

Researchers have tested this directly. In one study, ten young men held a submaximal isometric elbow extension until failure with the shoulder at either 0 or 90 degrees of flexion. Long head activity near the end of the hold was greater at 90 degrees, while no other portion of the triceps showed an effect of shoulder angle (Davidson & Rice, 2010). The authors also point out that readings from one head do not represent the whole group.

A 2018 study compared overhead and lying dumbbell extensions in 21 resistance-trained men, recording the long and lateral heads. Both exercises showed similar activation patterns across the range of motion, and the authors suggested the two should not both be prescribed in the same routine (Alves et al., 2018). That is a surface EMG study, so it tells us about activation, not about muscle growth.

What does growth data say about the three heads?

This is where the anatomy becomes useful. In a 2023 trial, 21 adults trained one arm with cable elbow extensions overhead and the other arm with the arm in a neutral position by the side. Both arms did 5 sets of 10 reps at 70% of one-rep max, twice a week, for 12 weeks. MRI showed larger gains in the overhead arm for every part of the muscle: the long head grew 28.5% vs 19.6%, the lateral and medial heads together 14.6% vs 10.5%, and the whole triceps 19.9% vs 13.9% (Maeo et al., 2023).

Two details stand out. The overhead arm used lower absolute loads (34-39% lower) and still grew more. And the lateral and medial heads, which do not cross the shoulder, also benefited. The authors link this to training at longer muscle lengths, though the trial itself cannot prove why. It is one study in 21 adults, so I would call the direction convincing and the exact size uncertain. We go deeper on this in overhead vs neutral triceps training.

Is there really a “workhorse” medial head and a “sweep” lateral head?

Gym language gives each head a personality. The medial head is the workhorse that fires on everything, the lateral head is the sweep that needs heavy loads, and the long head is the mass builder. It is a tidy story, and the data are more mixed.

In a 2021 study, 17 adults (7 men, 10 women) did isometric force-matching tasks at 20-80% of maximum, at elbow angles of 60, 90 and 120 degrees. Surface EMG from the three heads did not differ significantly, apart from one small difference between the medial and lateral heads at 20% effort with the elbow at 60 degrees. At 90 degrees or more flexed, the three heads were activated at matched levels relative to force (Akima et al., 2021). So under these conditions there was no clear sign that one head does the work alone.

On fibre type, biopsies of the lateral head in 15 professional tennis players showed roughly two thirds type 2 (fast-twitch) fibres (Sanchís-Moysi et al., 2010). That supports the idea that triceps handle heavy, explosive work well. But it is a small group of racket-sport athletes, it covered only the lateral head, and it does not show that lighter sets grow the muscle any less.

How is the triceps built inside, and why does it matter?

The triceps is a pennate muscle, meaning its fibres sit at an angle to the line of pull instead of running straight along it. In a 2011 study, 40 untrained men trained for 12 weeks (with 9 more as controls), and thickness and fibre angle of the long head were measured at three sites along the arm. Both increased at all three sites with no significant difference between them, which the authors attribute to the pennate fibre arrangement. The biceps, in contrast, grew more at its upper site than its lower one (Matta et al., 2011).

For you, that suggests the long head tends to grow fairly evenly along its length, so you do not need special tricks to “target the lower part.” It is also worth noting that these were untrained men, so results in experienced lifters may differ.

Muscle size also matters more than fibre geometry for strength. In Japanese Olympic athletes, the male-female difference in elbow extension force was mostly explained by cross-sectional area rather than differences in fibre angle (Ichinose et al., 1998). More triceps, stronger lockout.

What is horseshoe triceps, and can you build it?

Horseshoe triceps is a look, not an anatomical term. From behind, a developed lateral head forms the outer curve, the long head fills the inner line, and the medial head shows at the lower arm, giving a “U” outline when the arm is flexed.

Honest answer: how that looks depends on how much triceps you carry and on your own muscle shape and tendon length, which are inherited. Nobody can promise you a specific shape. What you can control is the size of the whole muscle:

1. Train through a full range, ending in a hard lockout.
2. Include an overhead movement for the long head.
3. Add load or reps over time.
4. Keep body fat low enough that the separation shows.

How should you train the three heads?

Use two movements per session, one overhead and one with the arm by your side. This covers the long head’s stretch demand and still allows heavy loading.

Overhead extension (long head emphasis). A cable or dumbbell extension with the arm overhead. This is the movement the 2023 trial used. Our guide to overhead cable extensions vs pushdowns covers setup and loading in detail.

Arm-by-your-side movement. Pushdowns, close-grip bench or dips let you use more weight. See straight bar vs V-bar vs rope pushdowns for how to choose, and close-grip bench press and wrist spacing if you press.

Dose. Start with 2-3 hard sets of each, 6-15 reps, 1-3 reps from failure, twice a week. If your elbows complain, back off the volume and read our piece on skull crushers and elbow pain. Pain that persists, or comes with swelling, numbness or weakness, is a reason to see a doctor or physio.

If you want a ready structure, our free push day plan already places triceps work after pressing. And for the other side of the arm, see functional anatomy of the biceps and brachialis. Want to chase the lateral head specifically? Cross-body cable extensions are one option, though evidence for isolation is limited.

Quick reference

Head	Starts on	Crosses	Shoulder position matters?
Long	Shoulder blade	Shoulder and elbow	Yes, stretched when the arm is overhead
Lateral	Upper arm bone (outer side)	Elbow only	No
Medial	Upper arm bone (deeper)	Elbow only	No

The bottom line

All three triceps heads straighten the elbow, and no exercise isolates one of them. The long head is the exception that matters, because it crosses the shoulder: stretch it with an overhead movement and growth was larger in every head in the one MRI trial we have. Pair that with a heavier arm-by-your-side lift, train close to failure, and let the horseshoe take care of itself. The evidence here is mostly from short trials and small samples, so treat this as a well-supported starting point and adjust to how your own arms respond.