Context: Muscle fatigue due to repetitive and prolonged overhead sports activity is considered an important factor contributing to impingement-related rotator cuff pathologic conditions in overhead athletes. The evidence on scapular and glenohumeral kinematic changes after fatigue is contradicting and prohibits conclusions about how shoulder muscle fatigue affects acromiohumeral distance. Objective: To investigate the effect of a fatigue protocol resembling overhead sports activity on acromiohumeral distance and 3-dimensional scapular position in overhead athletes. Design: Cross-sectional study. Setting: Institutional laboratory. Patients or Other Participants: A total of 29 healthy recreational overhead athletes (14 men, 15 women; age = 22.23 +/- 2.82 years, height = 178.3 +/- 7.8 cm, mass = 71.6 +/- 9.5 kg). Intervention(s): The athletes were tested before and after a shoulder muscle-fatiguing protocol. Main Outcome Measure(s): Acromiohumeral distance was measured using ultrasound, and scapular position was deter-mined with an electromagnetic motion-tracking system. Both measurements were performed at 3 elevation positions (08, 458, and 608 of abduction). We used a 3-factor mixed model for data analysis. Results: After fatigue, the acromiohumeral distance increased when the upper extremity was actively positioned at 45 degrees (Delta = 0.78 +/- 0.24 mm, P = .002) or 60 degrees (Delta = 0.58 +/- 0.23 mm, P = .02) of abduction. Scapular position changed after fatigue to a more externally rotated position at 45 degrees (Delta = 4.97 degrees +/- 1.13 degrees, P < .001) and 60 degrees (Delta = 4.61 degrees +/- 1.90 degrees, P < .001) of abduction, a more upwardly rotated position at 45 degrees (Delta = 6.10 degrees +/- 1.30 degrees, P < .001) and 60 degrees (Delta = 7.20 degrees +/- 1.65 degrees, P < .001) of abduction, and a more posteriorly tilted position at 0 degrees, 45 degrees, and 60 degrees of abduction (Delta = 1.98 degrees +/- 0.41 degrees, P < .001). Conclusions: After a fatiguing protocol, we found changes in acromiohumeral distance and scapular position that corresponded with an impingement-sparing situation.