The Anatomy of the Biceps

Complex muscle involved in flexion and supination

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The biceps is a large muscle situated on the front of the upper arm between the shoulder and the elbow. Also known by the Latin name biceps brachii (meaning "two-headed muscle of the arm"), the muscle's primary function is to flex the elbow and rotate the forearm. The heads of the muscle arise from the scapula (shoulder blade) and combine in the middle arm to form a muscle mass. The other end attaches to the radius, the outermost of the two bones that make up the forearm.

Anatomy

The biceps is one of four muscles alongside the brachialis, brachioradialis, and coracobrachialis muscles, that make up the upper arm.

The term biceps is both singular and plural. A single muscle is described as biceps, not bicep.

The biceps muscle is comprised of two heads. At each end are connective tissues called tendons that anchor the muscles to bone.

  • The long head originates from a cavity in the scapula called the glenoid. It passes through the shoulder joint to the upper arm through a groove in the humerus (the large bone of the upper arm).
  • The short head originates from a projection on the scapula called the coracoid and runs alongside the long head on the inside of the arm.

The two heads join in the middle arm to form a combined muscle belly. Although the heads work in tandem to move the forearm, they are anatomically distinct with no conjoined fibers.

As the heads extend downward toward the elbow, they rotate 90 degrees and attach to a rough projection just beneath the neck of the radius, called the radial tuberosity.

Of the other three muscles that make up the upper arm, the biceps is the only one to cross two joints: the elbow joint and the glenohumeral (shoulder) joint.

Function

Despite what some think, the biceps is not the most powerful flexor of the forearm. Although the biceps is the most prominent muscle of the upper arm, it serves to support and stabilize the deeper (and stronger) brachialis muscle whenever lifting or lowering the forearm.

The main functions of the biceps are the flexion and supination (outward rotation) of the forearm. This is facilitated, in part, by the 90-degree rotation of the muscle as it connects to the radius.

As the biceps muscle contracts, it can do one of two things (or both together):

  • Aid the brachialis in the flexions (lifting) of the forearm
  • Aid the supinator muscle (which starts at the outer elbow and ends at the inner wrist) in rotating the forearm upward.

Although the supination of the forearm involves the biceps, pronation (in which the palm is turned downward) is facilitated by the brachialis and corresponding pronator muscles.

The biceps also weakly assists with arm movements at the glenohumeral joint, including forward flexion (lifting the entire arm forward), abduction (opening the arm to the side), and adduction (folding the arm across the body).

The small head of the biceps is important in stabilizing the scapula, allowing us to carry heavy weights when the arm is in an extended downward position.

Nerve Supply

The movements of the biceps are facilitated by the musculocutaneous nerve which runs from the cervical (neck) spine and ends just above the elbow. The brachialis and coracobrachialis muscles are also serviced by the nerve.

In addition to directing the contraction of muscles, the musculocutaneous nerve (also referred to as the fifth, sixth, and seventh cervical nerves) provide sensations to the outer side the forearm from the elbow to the wrist. 

A separate nerve, known as the radial nerve, services the brachioradialis muscle.

Associated Conditions

Because the biceps are involved in such vital tasks as lifting and gesturing, the tendons and tissues that make up the muscle are vulnerable to harm. Most occur as a result of physical trauma or repetitive activity.

Among some of the more common conditions affecting the biceps:

  • Biceps strains occur when the muscle is overstretched or "pulled," causing some of the muscle fibers or tendons to tear. Sudden pain and swelling are common.
  • Partial tendon tears involving either the proximal tendon near the shoulder or the distal tendon near the elbow are characterized by pain, swelling, and an odd bulge at the site of the injury. In addition to physical trauma, the degeneration of the tendon due to age or repetitive use can cause partial tears.
  • Complete tendon tears occur when a biceps tendon ruptures and separates from the scapula or, less commonly, the elbow. The injury is often recognized by an audible "pop" followed by immediate pain and the loss of strength in the arm. An abnormal bulge known as a "Popeye deformity" will sometimes develop, caused when the tendon recoils from its incision point like a rubber band.
  • Insertional tendonitis is the inflammation of the tendon at the site where it connects with bone. It may be caused by a sudden increase in physical activity or the repetitive flexure or supination of the joint (such as twisting a screwdriver). Joint pain, inflammation, and the restriction of motion are common.

While some conditions, like minor sprains or contusions, can be diagnosed with a physical exam, others may require lab tests to detect inflammation in blood or joint fluid and/or imaging tests like X-ray, ultrasound, or magnetic resonance imaging (MRI) to check for rupture, bleeding, or other soft tissue injuries.

Treatment

Most injuries involving the biceps will heal on their own without the need for surgery. Acute injuries may be treated for the first 48 to 72 hours with a therapeutic practice known by acronym RICE, which involves:

  • Rest to protect the injured shoulder, arm, or elbow
  • Ice application, using an ice pack three or more times per day for 10 to 20 minutes to reduce swelling
  • Compression, using an elastic bandage to decrease swelling and help immobilize the injured shoulder or elbow
  • Elevation, propping the injured elbow above the heart to decrease blood flow to alleviate inflammation

Nonsteroidal anti-inflammatory drugs like Advil or Motrin (ibuprofen) or Aleve or Naprosyn (naproxen) can help reduce pain and swelling.

Intra-articular cortisone injections may also be used to temper pain and inflammation associated with chronic tendinitis. The most severe injuries may require surgery and postoperative physical therapy to regain strength and range of motion in the affected arm.

Corrective surgeries are typically reserved for elite athletes or people with severe ruptures or intractable pain in whom conservative treatments have failed.

Biceps Tenodesis

Biceps tenodesis is used to treat chronic or severe shoulder pain caused by a biceps tendon injury. The procedure, performed under general anesthesia, will either directly repair the tendon or use hardware to secure the compromised tissue.

Among the approaches:

  • Arthroscopic surgery, also known as keyhole surgery, involves a narrow fiber-optic scope and specialized tools to stitch the ruptured tendon without the need for large incisions.
  • The PITT technique is an arthroscopic procedure in which two needles create interlocking sutures to attach the proximal bicep tendon to shoulder ligaments.
  • The screw fixation technique involves the insertion of the ruptured tendon into a drilled hole in the arm bone which is then secured with a stainless steel screw.
  • The endobutton technique also involves the insertion of a ruptured tendon into a drilled hole. The tendon is then attached to a button on the opposite side of the hole which is twisted to create the appropriate tension.

Recovery from tenodesis varies but typically requires an arm sling for the first few weeks followed by four to six weeks of physical therapy. Strenuous activities can be usually be resumed in three months.

Recovery may take longer if more than one procedure is performed. One example is a SLAP repair surgery used to fix the tendon encircling the glenoid where proximal bicep tendon is attached.

Biceps Tenotomy

Biceps tenotomy, also known as a tendon release, is an arthroscopic procedure in which the proximal tendon is severed and allow to hang down the upper arm. It is a fast and effective way to treat pain without compromising the integrity or stability of the shoulder.

Tenotomy is reserved for sedentary people who are less likely to notice any difference in arm strength or function after surgery.

Tenotomy is less reasonable for athletes who may experience a marked loss of strength or develop spasms when weightlifting or doing repetitive turning motions (like rowing). A Popeye deformity is also possible.

Recovery from a biceps tenotomy is usually faster than tenodesis but involves more or less the same rehabilitation program.

Rehabilitation

A structured program of physical therapy and rehabilitation is considered essential following tenodesis or tenotomy. Without them, the odds of fully recovery biceps strength, mobility, and range of motion (ROM) are low.

The program is generally broken into three stages:

  • Phase 1, also known as the passive ROM stage, starts immediately after surgery and lasts for two weeks. It aims to prevent the fibrosis (scarring) and calcification of tendons which can lead to stiffness. Exercises may include ball squeezes, shoulder pendulum movements, and the flexion/extension or supination/pronation of the affected arm.
  • Phase 2 is the active ROM stage which generally lasts two weeks. Performed after the arm sling is removed, it increases the intensity of ROM exercises once healing has progressed. Exercises such as cross-body stretches, towel shoulder stretches, and the "sleeper stretch" (in which you lie on your side atop the affected shoulder) may be added.
  • Phase 3 is the strengthening phase which lasts for two more weeks (for a total of six weeks). This phase aims to build lean muscle mass in addition to flexibility. Physical therapy may include rowing exercises, light barbell curls, and resistance band training.

Athletes and active adults may embark on an additional two weeks of advanced strength training to restore them to peak performance.

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