Changes in infraspinatus cross-sectional area and shoulder range of motion with repetitive eccentric external rotator...

Repetitive eccentric loading results in muscle damage and subsequent changes in muscle stiffness and edema accumulation, which manifest as reduced joint range of motion and increased muscle cross-sectional area. The purpose of the study was to evaluate changes in shoulder range of motion and the infraspinatus cross-sectional area with repetitive eccentric contraction.

Twenty physically active participants performed 9 sets of 25 repetitions of eccentric external rotator contractions. The ultrasonographic measurement of the infraspinatus cross-sectional area, and shoulder internal/external rotation and horizontal adduction range of motion were measured before, immediately after, and 24h after the intervention.

Infraspinatus cross-sectional area significantly increased from baseline immediately after exercise (P<0.001), and remained elevated from baseline at the 24-hour follow up (P<0.001). Internal rotation and horizontal adduction range of motion did not change significantly between baseline and post-exercise (P>0.05), but were significantly decreased at the 24-hour follow up from the baseline (internal rotation: P<0.001, horizontal adduction: P<0.001) and the immediate post-exercise (internal rotation: P=1.012, horizontal adduction: P=0.016).

These changes observed after the eccentric contractions may have implications for injury development in pitchers, because 1) the infraspinatus endures repetitive eccentric loading with pitching and 2) decreased internal rotation and horizontal adduction range of motion have been linked to upper extremity injuries. However, since the muscle response after eccentric loading varies by the task and previous exposure to similar stress, future study needs to investigate the time course of recovery of the muscle cross-sectional area and range of motion after pitching in competitive pitchers.