Kinematic analysis of underwater wave swimming in the dorsal position for competitive swimmers

Abstract

Background: The underwater undulatory swimming (NOS) is a part of competitive swimming events where the  forward water resistance is practically halved compared to the surface swim. This makes  speeds achieved the fastest of all the strokes after the start and turn.

Objetives: i) To apply kinematic analysis techniques for the evaluation of the underwater undulatory swimming in competitive backstroke swimmers and ii) To compare the underwater performance between the first and the last underwater kicking dorsal position.

Method: 42 swimmers, 28 female and 14 male performed a 25-meter sprint from a push start and at maximum speed in dorsal position. They were filmed with two sequential cameras (50Hz) from a lateral underwater view for approximately 15 meters. The free software Kinovea 0.9.1 was used to digitize the articular points of the first and last underwater kick.

Results: The loss of velocity in boys was 10.37% compared to girls (16.39%). The loss of amplitude in both sexes was relatively similar (9.95% and 10.15%). While the loss of frequency was higher in boys compared to girls (8.32% vs. 7.41%). On the other hand, the body joint with the greatest angular variation between the first and last beat was the ankle, varying nearly 20 degrees in the downward phase in boys. In contrast, the shoulder and hip did not deviate more than 20 degrees from the straight line in any of the positions.

Conclusions: There is a loss of velocity between the first and last beat (8% - 10%) due to a decrease of the frequency and the length of the kick. Then, the angular variables between the first and last kick showed few differences. This information represents one of the few scientific evidences of the kinematic behavior of competitive swimmers during the undulatory dorsal wave stroke.

Keywords: Underwater wave motion, stroke frequency, stroke amplitude, backstroke.