Houel, N., Elipot, M., Andrée, F., & Hellard, P. (2010). Kinematics analysis of the undulatory underwater swimming during a grab start of national level swimmers. A paper presented at the XIth International Symposium for Biomechanics and Medicine in Swimming, Oslo, June 16–19, 2010.

This study estimated the most important factors that swimmers (N = 12) could use to improve performance. The underwater sections of competitive starts were analyzed. The following variables were defined: the horizontal velocity of the center of mass and the hip; the angle of attack of the trunk, thigh, leg, and foot; the mean kick frequency; the mean kick amplitude; and the phase time of the knee and the ankle. The effects of the independent variables on the dependent variables (velocities of the center of mass and the hip) were analyzed.

Different parameters influenced the horizontal velocities of the center of mass and the hip at different phases of the underwater undulatory swimming. Between 5.5 to 6.5 m, the stepwise regression analysis showed that the decrease of angles of attack of different segments (trunk at 5.5 m, foot at 6 m, thigh at 6.5 m) were selected variables to improve the horizontal velocities of the center of mass and the hip. From 6 to 7.5 m, an increase of the phase time (knee and ankle) improved the horizontal velocities of the center of mass and the hip. At 6.5 m, a decrease of the angle of attack of the thigh and an increase of the phase time of the knee were the best predictors for improving the two dependent variables. At 7.5 m, an increase of phase time of the knee and the mean kick frequency were the variables to improve the two horizontal velocities.

Implication. Undulatory underwater swimming should stress holding the torso (plus head and arms) stable while kicking involves the lower trunk through the hip to the ankles. There should be no change in amplitude of the hip or ankle movements throughout the underwater action. The undulation moves from the lower trunk through the hips down to the ankles. Apparently, the pressure of the water moves the feet into the most natural positions possible to develop final propulsion (much like a set of flippers).

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