In which shoulder movements does biceps tendonitis typically worsen?

Biceps tendonitis is an overuse injury that affects the biceps tendon, which runs along the front of the shoulder and connects the biceps muscle to the shoulder joint. One of the primary mechanisms behind the aggravation of biceps tendonitis is the positions and movements that place greater strain on the tendon.

When considering the shoulder movements that typically worsen biceps tendonitis, abduction and external rotation are particularly significant. Abduction of the shoulder raises the arm out to the side, which places tension on the tendon as it passes through the bicipital groove of the humerus. Additionally, external rotation further increases the strain on the biceps tendon, particularly when the arm is elevated, causing the tendon to come into contact with surrounding structures and potentially become more irritated.

In contrast, shoulder flexion and internal rotation may not elicit the same level of discomfort because these movements involve different mechanics that do not place as much load directly on the biceps tendon. Extension and adduction also do not significantly aggravate the condition as they do not require the same range of motion or load on the tendon. Thus, abduction and external rotation are the movements most likely to exacerbate symptoms of biceps tendonitis, making this the correct answer.