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The aim of this study was to compare the nonlinear properties of the four competitive swim strokes. Sixty-eight swimmers performed a set of maximal 4x25m using the four competitive swim strokes. The hip’s speed-data as a function of time was collected with a speedo-meter. The speed fluctuation (dv), approximate entropy (ApEn) and the fractal dimension by Higuchi’s method (D) were computed. Swimming data exhibited nonlinear properties that were different among the four strokes (14.048≤dv≤39.722; 0.682≤ApEn≤1.025; 1.823≤D≤1.919). The ApEn showed the lowest value for front-crawl, followed by breaststroke, butterfly and backstroke (P<0.001). Fractal dimension and dv had the lowest values for front-crawl and backstroke, followed by butterfly and breaststroke (P<0.001). It can be concluded that swimming data exhibits nonlinear properties, which are different among the four competitive swimming strokes.