Comparison of Classical Kinematics, Entropy, and Fractal Properties As Measures of Complexity of the Motor System in Swimming

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.