The long head is the largest of the three sections that make up your triceps, and it’s the only one that crosses both the shoulder and the elbow. While the lateral and medial heads attach to the upper arm bone, the long head anchors to your shoulder blade, giving it a unique role in arm movement and that coveted “horseshoe” shape on the back of the upper arm.
Where It Attaches
The long head originates on a small bony bump on the shoulder blade called the infraglenoid tubercle, which sits just below the shoulder socket. From there, it runs down the back of the upper arm and joins the other two triceps heads into a single tendon that inserts into the olecranon process, the bony point of your elbow. This dual attachment is what makes the long head unique. The lateral and medial heads both start on the humerus (upper arm bone), so they only act on the elbow. The long head’s connection to the scapula means it has a job at the shoulder as well.
What the Long Head Does
All three heads of the triceps work together to straighten your elbow, the muscle group’s primary function. Pressing a door shut, throwing a ball, doing a push-up: any time your arm extends, the triceps are firing.
The long head pulls double duty. Because it crosses the shoulder joint, it also helps extend your arm backward (pulling it behind you) and adduct your arm (bringing it closer to your body from a raised position). When your arm is extended, the long head can pull upward on the humerus, drawing it in toward the torso. This makes it active in movements like pulling, rowing, and any motion where you drive your elbows behind your body.
Its fiber composition reflects this versatility. The long head contains a relatively balanced mix of fast-twitch and slow-twitch muscle fibers, meaning it contributes to both explosive power and sustained, lower-intensity effort.
Why It Matters for Arm Size
The long head makes up the most visible mass on the inner, rear portion of your upper arm. If you flex your triceps in a mirror, the long head is the thick ridge running closest to your body. Building it is what creates the full, three-dimensional look most people associate with well-developed arms. Since the triceps as a whole account for roughly two-thirds of upper arm size, the long head is arguably the single most important muscle for overall arm thickness.
How to Target It With Training
Here’s the practical takeaway of the long head’s shoulder blade attachment: because it crosses the shoulder, its stretch and engagement change based on where your arm is positioned. When your arm is overhead, the long head is pulled to its longest length. When it’s behind your body, it’s shortened. Moving through both positions is how you fully work the muscle.
A 2023 study published in the European Journal of Sport Science found that triceps growth was substantially greater when elbow extension exercises were performed in an overhead arm position compared to a neutral (arms-at-your-sides) position. The overhead position places the long head under a deeper stretch at the bottom of each rep, and training muscles at longer lengths has consistently been linked to greater hypertrophy.
Exercises that place your arms overhead are especially effective:
- Overhead dumbbell or cable extensions stretch the long head to its greatest length at the bottom of the movement.
- Skull crushers (lying triceps extensions) allow the arms to drift slightly behind the head, creating a moderate stretch.
- Incline overhead extensions combine the overhead position with gravity to maintain constant tension through the full range.
Maintaining tension in that stretched position, rather than locking out quickly at the top, is key to maximizing the stimulus on the long head specifically. Exercises like pushdowns, where your arms stay at your sides, still work the triceps but shift more of the load to the lateral and medial heads because the long head is never fully lengthened.
Common Injuries and Pain
The most frequent issue involving the long head is triceps tendonitis, an overuse condition that causes pain along the tendon or at its insertion point on the back of the elbow. You’ll typically notice tenderness right at the bony tip of the elbow, and the pain gets worse with resisted extension, like pushing yourself up from a chair or locking out a bench press. Some people also experience swelling around the elbow and a noticeable weakness during any pushing movement.
Tendonitis here tends to develop gradually from repetitive loading, particularly in people who do a lot of pressing exercises or overhead work without adequate recovery. Pain that only appears during forced extension against resistance, rather than at rest, is a hallmark sign. Reducing training volume, addressing any sudden spikes in load, and allowing the irritated tendon time to recover are the typical first steps.
Because the long head attaches to the shoulder blade near the joint capsule, some researchers have speculated it may play a role in shoulder stability, though this hasn’t been clearly established. What is clear is that overhead movements place significant demand on the long head’s origin point, so persistent shoulder pain during overhead triceps work is worth paying attention to.
Long Head vs. Lateral and Medial Heads
The three heads of the triceps share a common insertion at the elbow but differ in where they originate and what they respond to. The lateral head, which forms the outer sweep of the arm, attaches high on the back of the humerus. The medial head, largely hidden beneath the other two, attaches lower on the humerus. Neither crosses the shoulder.
This means the lateral and medial heads are pure elbow extensors. They don’t care about arm position relative to the shoulder. The long head does. It’s most active when your arm is overhead or moving through a full arc from above the head to behind the body. If your training only includes pushdowns and close-grip presses, you’re likely undertargeting the long head relative to the other two. Adding at least one overhead extension variation ensures all three heads get adequate stimulus.