How Repetitive are Karate Kicks Performed by Skilled Practitioners?

Abstract

The aim of this paper is to propose the DTW-based signal comparison method that allows comparing motion capture (MoCap) measurements obtained from athletes even with different body proportions. We have applied the proposed framework to evaluate how repetitive are popular karate kicks performed by skilled athletes. The repetition level is defined with DTW distances and alignments of preprocessed MoCap data of a single activity performed by the same person. This knowledge is an important step to prepare tabularized norms which can be used as very useful tool by sport society to improve the training with the aid of modern computer methods. With those norms we can tell which DTW distances are typical for highly skilled karateka. The maximal distance between two aligned trajectories might differs from 9.36 ± 2.08 cm for to even 29.21 ± 16.5 cm. This last situation is caused by the fact that a person can perform the same kick with large nonlinear temporal displacements of actions phase, however, we have to remember, that those displacements happen in time periods of about 0.05 seconds in length. The results we obtained are very important because they show what range values one should expect from this kind of comparison and might be a reference for other scientists.