Shoulder range of motion A gain in shoulder external rotation range of motion (ERG) and a decrease in internal rotation range (GIRD) is found on the dominant side in overhead athletes and is due to a combination of bony and soft tissue adaptations. 24 Increased humeral retroversion is a bony adaptation that is common in throwers, 25 , 26 , 27 whilst the soft tissue changes which lead to ERG and GIRD are:
- Acquired laxity in the anterior capsule due to high anterior shear forces in throwing
- Tightness in the posterior capsule as a result of stress during deceleration. Humeral retroversion is defined as the acute angle between the axis of the elbow joint and the centre of the humeral head. Throwers with increased humeral retroversion will present with ERG and GIRD, but their total range of motion may be similar on both the dominant and non-dominant sides.
It is a protective adaptation to throwing, allowing for greater range of external rotation without stressing the anterior capsule. The proximal humeral epiphysis is open between the ages of 12 and 16, and throwing during these ages causes this adaptation. Throwers with increased humeral retroversion have been found to be less likely to sustain shoulder and elbow injuries. 25 , 26 , 27 As humeral torsion influences shoulder rotation and horizontal flexion range of motion, it is important to account for this when screening throwers.
28 Humeral retroversion can be easily measured via ultrasound. If the athlete’s ERG is equal to GIRD, when corrected for humeral retroversion, then they are considered to have normal shoulder rotation ROM. If GIRD is greater than ERG when corrected for humeral retroversion, they are considered to have a restriction in their posterior shoulder. Changes in shoulder rotation have been found to occur immediately post throwing and over the course of a season, with GIRD found to increase.
29,30 It is therefore important to know a thrower’s shoulder rotation range pre-season and monitor this in-season. Regular mobility exercises to maintain range, particularly IR and horizontal flexion, should be completed in-season. Shoulder strength – Internal rotation strength has been found to increase, and external rotation strength decrease, in the dominant shoulder of throwers when measured both isokinetically and isometrically.
As a consequence, the ratio of external rotation strength to internal rotation strength has been found to reduce. 31,32 These changes are thought to be contributing factors to throwing injuries. 33,34 It is therefore important to assess rotator cuff strength pre-season and regularly monitor in-season in throwers to reduce injury risk. Regular cuff conditioning exercises should be completed to prevent reduction in cuff strength and minimise the risk of injury.