Dynamic acromiohumeral interval changes in baseball players during scaption exercises

HypothesisElevation of the arm during a dynamic scaption exercise will result in a progressive narrowing of the acromiohumeral interval (AHI); however, the addition of a load will not significantly affect the AHI in healthy baseball players.Materials and methodsThirteen healthy baseball players performed a seated scaption exercise from 0° to 90°, with and without a normalized additional load. Dynamic AHI intervals were measured using digital fluoroscopic videos with the arm at the side, and at 30°, 45°, 60°, and 75° of humeral elevation.ResultsThe mean AHI for unloaded and loaded scaption decreased significantly (P < .001) from the arm at the side (12.7 mm) until 45° (4.9 mm), further changes in the mean AHI between 45°, 60°, and 75° were not significantly different. Generally, loaded scaption resulted in smaller AHI values at 45°, 60°, and 75°; however, only the differences at 60° (P = .005) and 75° (P = .003) were significant.DiscussionNarrowing of the AHI during dynamic motion was similar to previous reports of static AHI, with the exception of the trend towards widening of the AHI seen at 75° during both conditions. The additional AHI narrowing observed at 60° and 75° during the loaded exercise may indicate that scapular positioning is more influential in this range.ConclusionAn additional AHI narrowing of 11% during loaded scaption, did not result in any clinical impingement during the exercise, but may have more serious implications in other healthy and pathologic populations.