Comparative Study of the Response of Kinematical Variables from the Hip and the Center of Mass in Butterfliers
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abstract
The aim of this study was to compare the intracyclic variation of kinematical variables from the
hip and the center of mass (CM) with the purpose to assess if the analysis of kinematical
variables of the hip might replace the study of the kinematical variables of the CM. Seven
Portuguese male swimmers of national and intemational levei were studied. Each swimmer
performed 3 sets of3x25 meters, at a constant velocity and as close as possible to the maximum,
using exclusively frontal inspiration cycles, lateral inspiration cycles and non-inspiratory cycles
in each set. Two pairs of cameras were used to create "dual media" images. Another cam era was
set behind an underwater window in the endwall. One last camera was placed above the water
surface. The study comprised the analysis of complete stroke cycles in buttert1y using the "Ariel
Performance Analysis System" from Ariel Dynamics Inc. Some of the correlations between the
maximal vertical amplitude of displacement of the hip and the CM didn't present significant
values. AlI the correlations between the horizontal velocity and horizontal acceleration of the
hip and the CM were significant in all breathing models. However, only one swimmer presented
in both cases r>=O.95. So, apparently, the hip does not represent properly the intracyclic
variations ofthe kinematical variables ofthe CM.
