The aim of our research was to assess sidetosidedifferences in morphology and function of the upper limbs in 11–12yearoldbaseball players. As the connectivetissue in boys at the onset of puberty can be particularly sensitive to intense eccentric exercise, we hypothesized that regular baseball playing can create asymmetryof individual muscle groups, and tendon and ligament morphology in young athletes.

The participants of this study were 14 male baseball players who participated 4 or more years in baseball activities (11.6 ± 0.6 year; playing experience, 4.5 ± 0.8years). We also recruited 16 untrained healthy control subjects (11.8 ± 0.7 years). Ultrasonography of the shoulder and elbow regions was performed using a GELogiq 7 ultrasound device with a 7–12 MHz linear probe. The thickness of the subscapular and supraspinatus tendon and the articular cartilage thickness of thehumeral head were assessed at the shoulder region. The thickness...

There were no sidetosidedifferences within groups for any of the measured ultrasound parameters (p>0.05, Fig.3). However, the supraspinatus tendon ofbaseball players was 0.08 cm thicker than that of the controls (p<0.05). The articular cartilage of the humeral head and ULC thickness were larger in baseballplayers compared with the controls (p<0.05). The medial ulnohumeral distance without valgus stress was greater for baseball players (p<0.05), but there was nosignificant difference between groups when the valgus stress test was used.

In the present study, ultrasound examination revealed no morphological sidetosidedifferences in baseball players, although some indices were different betweenplayers and untrained controls. Most pronounced was the thicker supraspinatus tendon and ulnar collateral ligament in baseball players than controls. Furthermore,the medial ulnohumeral distance was larger without applied valgus stress in baseball players than untrained controls. All of these differences seem to have arisen bycoincidence and are related more to the random selection of subjects than to adaptation to training.