The muscle on the back of your upper arm is the triceps. Its full name, triceps brachii, literally means “three-headed muscle of the arm,” because it’s made up of three separate sections that merge into one tendon at your elbow. It’s the largest muscle in your upper arm, taking up the entire back compartment, and it’s responsible for straightening your elbow every time you push, throw, or extend your arm.
Why It Has Three Heads
The triceps isn’t one simple slab of muscle. It has three distinct portions, each starting at a different point on your skeleton but all connecting to the same spot on the back of your elbow (a bony point called the olecranon, which is what you feel when you lean on your elbow).
The long head is the only section that crosses your shoulder joint. It starts on your shoulder blade, runs down the inside of your upper arm, and is the portion you can see and feel closest to your body. Because it crosses two joints, it plays a small role in pulling your arm backward at the shoulder and helping to stabilize the shoulder when your arm is raised.
The lateral head starts on the outer back surface of your upper arm bone (the humerus). It sits on the outside of the arm and is the section most visible when you flex from the side. It gives the triceps its characteristic horseshoe shape in people with well-developed arms.
The medial head lies deeper, underneath the other two. It has a broad attachment along most of the back of the humerus. Despite being the least visible, it’s the workhorse of the group: it fires during every type of elbow straightening, while the long and lateral heads only kick in when you’re pushing against real resistance.
What the Triceps Actually Does
Straightening your elbow is the primary job. Any time you push a door open, throw a ball, do a push-up, or simply reach your arm out in front of you, the triceps is the main muscle creating that motion. It opposes the biceps on the front of your arm: the biceps bends the elbow, and the triceps straightens it.
The long head also contributes to shoulder movement, specifically pulling your arm backward (like the follow-through of a swim stroke) and bringing a raised arm back down toward your body. That said, bigger muscles like the lats and rear deltoid do most of that work. The triceps’ shoulder role is minor enough that most clinical shoulder exams don’t even test it.
A Small Helper Muscle at the Elbow
There’s also a small, triangular muscle called the anconeus that sits right at the back of your elbow, just below the triceps. You can feel it on the outer side of your elbow if you press while straightening your arm. It assists with elbow extension but contributes far less force than the triceps. Some anatomy references group it with the triceps, though technically it belongs to the forearm compartment.
Best Exercises for the Triceps
A study from the University of Wisconsin tested muscle activation across several common triceps exercises using sensors placed directly on the muscle. Triangle push-ups (also called diamond push-ups, where your hands form a triangle under your chest) produced the highest overall activation. Kickbacks and dips were statistically equal to triangle push-ups for both the long and lateral heads, making all three the top tier for triceps training.
Rope pushdowns, bar pushdowns, and lying extensions (sometimes called skullcrushers) produced significantly less activation than those top three. That doesn’t make them useless, but if you want the most efficient triceps work, triangle push-ups, kickbacks, and dips are the strongest options. One practical advantage of triangle push-ups and dips is that they require no equipment.
Common Triceps Injuries
The most frequent issue is triceps tendonitis, an overuse injury where the tendon connecting the muscle to the elbow becomes inflamed and painful. You’ll typically feel an ache at the back of the elbow, sometimes with swelling, weakness when straightening your arm, or a visible bulge near the elbow. Activities that involve repetitive pushing or impact are the usual culprits: bench pressing, throwing, hammering, or catching yourself on an outstretched hand during a fall.
Risk factors include skipping warm-ups, poor exercise form during repetitive movements, and certain conditions like rheumatoid arthritis or diabetes that affect tendon health. Anabolic steroid use also increases risk.
Most cases respond well to rest, ice (15 to 20 minutes at a time, wrapped in a towel), compression with an elastic bandage, and keeping the arm elevated. Anti-inflammatory pain relievers can help manage swelling. If those measures don’t resolve it, options include corticosteroid injections, platelet-rich plasma therapy, or physical therapy. Surgery to repair or graft the tendon is a last resort when conservative treatment fails.
The Nerve That Controls It
The triceps is powered by the radial nerve, which runs from your neck (nerve roots C5 through T1) down the back of your arm. This nerve travels through a groove that spirals around the humerus, which makes it vulnerable when the upper arm is injured. A fracture of the humerus or prolonged pressure on the back of the arm (sometimes called “Saturday night palsy” from draping your arm over a chair while sleeping) can damage the radial nerve.
Damage high up, near the armpit, typically weakens the triceps and causes wrist drop, where you can’t lift your hand at the wrist. Injuries lower down, in the spiral groove of the humerus, often spare the triceps because the nerve branches to the muscle have already split off above that point. In those cases, wrist and finger extension are affected while elbow straightening stays intact.