Shoulder Mobility, Humeral Retrotorsion and Serve Biomechanics

Fredrik explains that external rotation increases and internal rotation decreases with age and throwing volume. Internal rotation deficit alone is no longer seen as equal to injury, since the serve uses long axis rotation, combining shoulder internal rotation with forearm pronation. A meta-analysis found that throwing athletes with limited external rotation in preseason had a higher injury risk, so mobility work should cover external rotation too. Heavy throwing in youth leads to humeral retrotorsion, a bony adaptation that stretching cannot change. Because the shoulder moves at around 2,000 degrees per second in tennis, he recommends slow-motion video to assess the serve. He shows how women's serves may use less long axis rotation and load the biceps more, and how opening the trunk too early creates shoulder lag. His clinical summary lists a weak infraspinatus, an overworked biceps, a fatigued subscapularis, posterior capsule changes, a shortened pectoralis minor and poor throwing mechanics, with the push-up as a useful exercise for young players.