<p>This study aimed to compare serratus anterior (SA), upper trapezius (UT), middle trapezius (MT), and lower trapezius (LT) activity between painful versus asymptomatic shoulders within the pain group, and swimmers with versus without pain. This cross-sectional study evaluated 16 competitive swimmers with and without shoulder pain. Normalized electromyography (EMG) recorded SA, UT, MT, and LT activation during push-up plus (PUP) exercise was collected and analyzed. Baseline characteristics were comparable between groups. During the push-up, no significant differences were found between swimmers with shoulder pain and asymptomatic swimmers in UT, MT, LT, or SA activity (<i>P</i> &gt; 0.05). In the hold task, UT, MT, and SA activities had no differences between groups or sides (<i>P</i> &gt; 0.05). However, LT activity was significantly different in swimmers with shoulder pain (F = 4.649, <i>P</i> = 0.040). Dominant and non-dominant sides had no differences in any muscle across both tasks (<i>P</i> &gt; 0.05). Scapular muscle activation patterns during PUP exercise were generally similar between swimmers with and without shoulder pain, as well as between painful and asymptomatic shoulders. The only notable difference was the LT activation during the hold task in swimmers with shoulder pain, suggesting a deficit in endurance-related control. For swimmers with shoulder pain, clinicians should prioritize LT assessment and endurance training within their routine practice.</p>