The use of surface electromyography for the analysis of muscle activity in swimming has proven to be a valuable tool for understanding neuromuscular activation patterns during the technical movement. However, one of the persistent methodological challenges is the lack of consensus on data normalization procedures, which makes comparisons across studies difficult and compromises the validity of the results. In the specialized literature, specifically in the field of swimming, the two most commonly used strategies are Maximum Peak (MPx) normalization (dynamic conditions) and Maximum Voluntary Contraction (MVC) normalization (static conditions). Several studies have indicated the limitations of both methodologies; however, it is still unclear which is most appropriate in the context of high-speed cyclic movements. The objective of this study is to compare the use of the two types of normalization in the electromyographic analysis of the butterfly stroke, based on a case study of an elite swimmer. For this purpose, an electromyography system was used during the execution of the butterfly stroke under simulated conditions (out of the water). Eight sensors were placed on upper body muscles, four on the left side and four on the right side, selected for their role in stroke performance. The recording was obtained from a 1-min technical performance at maximum intensity, specifically in the sliding window between 37 and 39 s. For normalization in both methods, the maximum peak value, percentage of activation relative to the peak, and symmetry index were determined. Signal processing was then performed, and both normalization methods were applied to determine methodological differences and their impact on data interpretation.