Since the collagen strands in the tendons are lined up, tendons have high TENSILE STRENGTH, meaning they can withstand high forces that pull on either end of the tendon. When muscles work, they pull on one end of the tendon. While the other end of the tendon pulls on the bone, causing the bone to move. So, if we think of the bicep, contracting the biceps muscle can bend the elbow upward and the biceps can also help flex the shoulder, lifting the arm up, the muscle can also rotate, or twist, the forearm in a way that points the palm of the hand up. This movement is called SUPINATION, which positions the hand as if you were holding a tray. Now what can lead to a tendon being inflamed and leading to tendonitis? In most cases tendonitis, will result from repetitive shoulder actions that can result in overuse of the biceps tendon.