Crawlers swim in different manners in a swimming flume to measure water resistance. (Provided by the University of Tsukuba)

Freestyle swimmers beware. Kicking may bring no benefit when trying to swim the front crawl faster, according to researchers from the University of Tsukuba and the Tokyo Institute of Technology.

While kicking is essential in lifting the lower half of the body to keep the crawler in a horizontal position and is believed to help reduce resistance, the scientists discovered leg movements generate significant resistance when swimming speed exceeds a certain level.

The discovery is expected to influence methods of teaching swimmers how to crawl faster, including elementary school students.

“Kicking water flexibly, not swinging the legs widely, and improving skills to manipulate the upper half of the body to better catch water will lead to time improvement,” said Hideki Takagi, a sports engineering professor at the University of Tsukuba.

The team’s findings have been published in the Journal of Biomechanics, which features articles related to bioengineering.

When a crawler attempts to swim faster, they need to whirl the arms quickly. But as the legs move simultaneously with the arms, whirling the arms faster inevitably results in an increasing number of kicks.

The researchers measured the resistance between the body and water by having subjects fixed with wires swim in a flume in three different manners: swimming with both arms and legs; crawling with arms alone; and by simply stretching the body straight.

The results showed kicking water provided a propulsive force when swimming at a relatively low speed of 1.1 meters per second, a level at which one can swim 100 meters in 90.91 seconds.

However, when the swimming speed exceeded 1.3 meters per second, a figure that allows the swimmer to finish a 100-meter race in 76.92 seconds, leg movements hampered water flow and produced resistance equivalent to the cube of the speed ratio.