The biceps is a large and thick muscle on the ventral portion of the upper arm. It is composed of a short head (caput breve) and a long head (caput longum).
The short head originates from the tip of the coracoid process, and the long head originates from the supraglenoid tubercle (tuberculum supraglenoidale) of the scapula. Both heads insert on the radial tuberosity and the fascia of the forearm via the bicipital aponeurosis.
More specifically, the short head inserts on the bicipital aponeurosis (aponeurosis musculi bicipital brachii) to the fascia (fascia antebrachii) on the medial side of the forearm. The long head of the biceps inserts on the radial tubercle (tuberositas radii), travels through the shoulder joint and descends through the intertubercular groove of the humerus.
The long head adducts and internally rotates the humerus while the short head abducts the humerus. One of the most important functions of the biceps is elbow flexion. When both heads contract it will bend the elbow and cause supination. The biceps also support the humeral head within the glenoid cavity.
The biceps muscle can be assessed while the patient is in a seated or supine position. The elbow should be fixed with one hand to cushion it from any pressure from the table. With the forearm in supination, the health case provider can then check for elbow flexion. The patient should also be asked to lower the forearm against resistance.
To check for weakness, the health care provider should check the arm for flexibility of the forearm against gravity. Also, observe the patient during eating or combing hair.
The brachial artery that arises from the axillary artery supplies the biceps and is a main source of blood for the arm.
The nerve supply to the biceps is provided by the musculocutaneous nerve (root C5, C6), which also supplies the brachialis muscle and the coracobrachialis muscle.
Even though the biceps muscle in most people has 2 heads, it is also one of the most variable muscles in the body. At least 30% if adults have some variation in the origin of the muscle. In many patients, a third head may arise from the humerus, but in about 2% to 5% of people, there may be supernumerary heads numbering 3 to 7.
The distal biceps tendon may be bifurcated in about 20% or be completely separated in about 40% of individuals. These variations have no adverse effect on arm function.
Surgery is the last treatment for a biceps muscle tear. It is only done when the tear is severe, and there is no chance that conservative treatment may help. Furthermore, surgery is often considered in professional athletes as it allows for a faster recovery. The surgery should generally be done after the initial edema and inflammation have subsided, which takes 2 to 3 weeks. Long delays are not recommended as this may lead to scar formation and fixation of the elbow in one position. There are several procedures to repair the ruptured biceps tendon. Both the proximal and distal tendon can be reattached using small incisions. The ruptured tendon may be reattached with sutures or with the use of suture anchors. Complications of surgery include:
Conditions Seen in the Biceps
Usually, bicipital tendinitis is a result of impingement or tearing of the rotator cuff. The function of the long head of the bicep is to act as a humeral stabilizer and decelerate elbow extension. With the translation of the humeral head with additional activity, stress is placed on the bicep and ligament structures. The biceps brachii is susceptible to injury as a result of repetitive overuse and rapid overhead movements with shoulder abduction, external rotation and elbow flexion with supination. Excessive and prolonged irritation of the biceps tendon, repeated corticosteroid or traumatic injuries may cause tendon rupture and distal retraction of the muscle which can cause a lump in the forearm. 
Biceps Rupture Case
A bodybuilder may feel a sudden, loud pop while doing a set of heavy deadlifts with an underhand grip. He or she feels a sharp pain in his upper arm. They immediately grab the bicep as it contracts uncontrollably. There is swelling, bruising, and a large bulge from the deformed muscle.
Deficits in a Proximal Long Head Tear versus a Distal Tear
Proximal long head tears show mild weakness with elbow flexion. Distal tears show significant loss of supination
Distal rupture will cause swelling and bruising, as well as a hollow in front of the elbow created by the absence of tendon and bulge in the upper part of the arm due to recoiled shortened tendon.
Proximal rupture will cause bulging, bruising and muscle gathering (Popeye sign) with indentation closer to the shoulder
Importance of Manual Testing in Diagnosing a Partial Tear versus a Complete Tear
Partial tears are more difficult to diagnose and may require manual testing of the bicep muscle for a sign of pain with muscle activation.
Biceps Muscle Tear Diagnosis
One may use ultrasound or MRI to check for muscle tendon tear.
Treatment of Biceps Muscle Tear
The general treatment of a biceps muscle tear depends on the severity. In the majority of cases, conservative treatment will suffice. For the acute swelling, apply ice packs every 4 hours for 24 to 48 hours. This will reduce the swelling and pain. 
If the pain is moderate to severe, NSAIDs can be used for a few days.
Once the swelling and pain have subsided, the patient should undergo a physical therapy program to regain function and muscle strength.
Be aware that the biceps muscle can also give rise to rhabdomyosarcomas. Thus, if a lump is palpated, the patient should get an MRI. A needle biopsy is not recommended as it may lead to seeding. Complete excision is the goal.