The biceps is located on the front of your upper arm, between your shoulder and your elbow. It sits in what anatomists call the anterior compartment of the arm, meaning the side that faces forward when your palm is turned up. It’s the muscle you see bulge when you bend your elbow and flex.
Where Exactly the Biceps Sits
Your upper arm has two main compartments. The front (anterior) compartment houses the biceps, while the back (posterior) compartment houses the triceps. The biceps is the most superficial muscle on the front of the arm, meaning it’s the closest to the skin. Directly beneath it lies a deeper muscle called the brachialis, and beneath that is the humerus, your upper arm bone.
If you run your hand along the front of your upper arm, what you’re feeling is almost entirely the biceps. The thickest, most prominent part of the muscle belly sits roughly at the midpoint of the upper arm, about halfway between the bony bump near the front of your shoulder (the coracoid process) and the outer knob of your elbow.
How the Biceps Is Built
The biceps has two separate heads, which is where the name comes from (“bi” meaning two). Both heads originate on the shoulder blade, not on the upper arm bone itself. The long head starts at a small bump just above the shoulder socket, then threads through a groove on the front of the humerus called the bicipital groove. The short head starts at a bony projection near the front of the shoulder blade, closer to the chest.
These two heads merge into a single large muscle belly as they travel down the front of the humerus. At the bottom, the muscle tapers into a tendon that crosses the elbow and attaches to the radius, the forearm bone on the thumb side. The attachment point is a small raised area on the radius called the radial tuberosity, located just below the elbow joint.
What the Biceps Actually Does
Most people think of the biceps as the muscle that bends the elbow, and that’s correct. When you curl a dumbbell or pull a door handle toward you, the biceps contracts to bring your forearm closer to your shoulder. But bending the elbow is only part of the job.
The biceps is also the primary muscle responsible for supinating your forearm, which means rotating it so your palm faces up. Think of turning a screwdriver or opening a jar. That twisting motion relies heavily on the biceps. The short head also assists with pulling your arm inward toward your body, while the long head can help lift your arm out to the side when it’s already rotated outward.
Muscles That Surround It
The biceps doesn’t work alone on the front of the arm. The brachialis muscle lies directly underneath it, pressed against the humerus. The brachialis is actually a stronger elbow flexor than the biceps, but because it sits deeper, you can’t see or feel it as easily. A third muscle in the same compartment, the coracobrachialis, runs alongside the short head of the biceps near the shoulder and helps pull the arm forward.
All three of these front-compartment muscles are controlled by the same nerve, which runs from the neck down through the arm. If that nerve is damaged, you lose the ability to bend the elbow effectively and to rotate the forearm palm-up.
Where Biceps Injuries Happen
Because the biceps spans two joints (the shoulder and the elbow) and is anchored by tendons at both ends, it’s vulnerable to tears at either attachment point. The vast majority of biceps tendon ruptures, roughly 90 to 97%, occur at the top of the muscle near the shoulder, almost always involving the long head tendon. This makes sense given how the long head’s tendon takes a sharp turn through the bicipital groove at the top of the humerus, creating a natural stress point.
Tears at the bottom of the muscle, where the tendon connects to the radius near the elbow, are far less common. These distal tears typically happen during a sudden heavy load, like catching something unexpectedly heavy. A proximal tear near the shoulder often causes the muscle belly to bunch up lower on the arm, creating a visible lump sometimes called a “Popeye deformity.” A distal tear near the elbow tends to cause more noticeable weakness in forearm rotation and grip strength, since that lower attachment is critical for transferring force into the forearm.
How to Find It on Your Own Arm
Place your opposite hand on the front of your upper arm, then bend your elbow against light resistance. The firm mass you feel contracting is the biceps. If you trace upward toward the shoulder, you’ll feel the muscle narrow into tendons that disappear under the front of the shoulder. Trace downward toward the elbow, and you’ll feel the tendon become cord-like as it crosses the elbow crease and dives toward the thumb side of your forearm. That cord is the distal biceps tendon heading to its attachment on the radius bone.