Acute changes in supraspinatus and biceps longus tendon thickness due to pitching

This study aimed to (1) identify acute changes in supraspinatus and biceps longus tendon thickness after pitching and (2) determine the relationship between changes in tendon thickness and changes in glenohumeral range of motion (ROM) after pitching. Fourteen healthy males with at least 5 years of baseball experience as baseball players performed 100 full-effort fast ball pitches. Tendon thicknesses and the glenohumeral internal rotation ROM were measured before, immediately after, and 24 h after pitching. One-way repeated-measures analysis of variance or the Friedman test with Bonferroni post hoc comparisons was performed to compare changes in tendon thickness and glenohumeral ROM due to repetitive pitching and to identify the relationships between tendon thickness changes and changes in glenohumeral internal rotation ROM. The supraspinatus and biceps longus tendon thicknesses increased immediately (p<0.001) and 24 h after pitching (supraspinatus: p=0.024, biceps longus: p<0.001). Glenohumeral internal rotation ROM decreased immediately after pitching (p<0.001) but not at 24 h (p=0.086). Decreased glenohumeral internal rotation ROM was associated with increased supraspinatus tendon thickness immediately after pitching (r=-0.77, p=0.001). Our results suggest that it takes time for tendon swelling to improve in pitchers after high-velocity repetitive pitches.