Causes

Inflammation of the long biceps tendon is mostly due to prolonged overuse by repetitive overhead activities. It can also result from a sudden injury caused by an excessive force applied to the biceps tendons whilst lifting or carrying a heavy weight with the upper extremity. Additional factors can contribute to long biceps tendonitis:

Tear of the rotator cuff

Shoulder instability

Joint stiffness especially of the elbow

Lack of, or excessive training

Inadequate warm up

Weakness of the muscles

Tightness of the biceps