It is well accepted that the cocking phase of serve inflicts enormous stress & strain on the shoulder & medial aspect of the elbow (ulnar collateral ligament & common flexor tendons). This is due to immense shoulder external rotation (ER) in which the aforementioned joints must oppose in the subsequent acceleration phase. Although max ER during this phase embarks well known stresses, it is considered crucial for high velocity serving; a dilemma b/w performance & injury prevention.

Miyashita et al collected kinematic data of several baseball players to i.d. where max shoulder ER was coming from.

Results:
• Total max ER range of motion was 144°
• Component motions contributing to 144° ER:
1) Glenohumeral joint (shoulder) 105°
2) Scapula posterior tilt 23°
3) Thoracic spine (T/S) extension 9°

Hypothesis
- Total degree of ER motion from the contributing joints = 138°. This is 6° less than the total shoulder external range of motion calculated (144°).
- Potentially, the extra 6° was “compensated” by the elbow (elbow valgus).

Implication:
- Kabaets et al found inadequate T/S extension leads to decreased shoulder range of motion, posterior scapula tilting, & decreas in shoulder girdle muscle force.
- This may result in increased demand on the elbow & shoulder to achieve max external rotation during cocking phase & deleterious to the shoulder & elbow.
- Increased demand may lead to subacromial impingement syndrome (biceps, rotator cuff, bursa), labral tears, medial epicondylalgia & ulnar collateral ligament sprains.

PREHAB:
- Implementing T/S mobility interventions results in improved T/S extension & shoulder ROM. Performing these drills will result in improvement in all 3 components above!

Exercise:
1) Overhead Squat
2) Progression: Overhead Resisted Y Squat
- Keep thumbs pointed back & away to elicit more lower trap activation.