Abstract: Objective: This study aims at describing the swimmers’ features and changes of a short-cycle speed fluctuation in the 200m freestyle (Vfluc),and analyzing their correlation with the swimmers’ performance. Methods: 11 male swimmers in active service from Hubei are selected as the research subjects. 4 underwater and 2 overwater video cameras are used to synchronously record their swimming performance. The 200m freestyle swimming is divided into 4 segments (SC1, SC2, SC3, SC4) and oval region method is adopted to calculate human body data. Results: the findings indicate an overall decline in the Vmean and a positive correlation between the swimmers’ Vmax/Vmin and their performance with the correlation of segment 1 much higher than the other three sections. Vmax and Vmin demonstrate significant correlation, but no correlation to the swimming performance. Conclusion: there is no correlation between the velocity fluctuation characteristics in all directions and performance with no significant changes during the whole process.

Key words: kinematics, freestyle, centroid, velocity features