Courtesy of Effect of leg kick on active drag in front-crawl swimming: Comparison of whole stroke and arms-only stroke during front-crawl and the streamlined position, Journal of Biomechanics by Kenzo Narita of the University of Tsukuba, Motomu Nakashima of the Tokyo Institute of Technology, and Hideki Takagi of the University of Tsukuba.
Japanese scientists Kenzo Narita of the University of Tsukuba, Motomu Nakashima of the Tokyo Institute of Technology, and Hideki Takagi of the University of Tsukuba published a study called Effect of leg kick on active drag in front-crawl swimming: Comparison of whole stroke and arms-only stroke during front-crawl and the streamlined position in the Journal of Biomechanics that examined the effects of kicking.
In freestyle where your head swings from left to right on one axis and your arms rotate forwards in another axis and your legs move up and down and laterally in a third plane, inefficiencies are created at nearly every moment of your freestyle stroke.
The researchers explained their study, “The purpose of this study was to examine the effect of leg kick on the resistance force in front-crawl swimming.
The active drag in front-crawl swimming with and without leg motion was evaluated using measured values of residual thrust (MRT method) and compared with the passive drag of the streamlined position (SP) for the same swimmers.
Seven male competitive swimmers participated in this study, and the testing was conducted in a swimming flume. Each swimmer performed front-crawl under two conditions: using arms and legs (whole stroke: WS) and using arms only (arms-only stroke: AS). Active drag and passive drag were measured at swimming velocities of 1.1 and 1.3 m s−1 using load cells connected to the swimmer via wires. We calculated a drag coefficient to compare the resistances of the WS, AS and SP at each velocity.
For both the WS and AS at both swimming velocities, active drag coefficient was found to be about 1.6–1.9 times larger than that in passive conditions. In contrast, although leg movement did not cause a difference in drag coefficient for front-crawl swimming, there was a large effect size (d = 1.43) at 1.3 m s−1. Therefore, although upper and lower limb movements increase resistance compared to the passive condition, the effect of leg kick on drag may depend on swimming velocity.”
In other words, each swimmer swam first by swimming with his legs kicking normally, and then next by swimming normally without kicking. In this limited test, they wanted to see if kicking or not is actually helping forward progression dependent on the swimming speed.
They found that swimmers moving at 1.1 meters per second (or swimming 100 meters in 1:30.91) should kick. That is, at a pace of 1:30 per 100 meters, kicking has a positive effect on total forward momentum.
In contrast, if swimmers swim faster at 1.3 meters a second (or 100 meters in 1:16.92) or better, they found that kicking increases drag and slows swimmers down.
“This finding is interesting, but I personally would not place too much importance on this finding for open water swimmers,” says Steven Munatones. “Simply based on their findings, it would appear that somewhere between 1:16.9 and 1:30.9 pace per 100 meters, the pace with kicking and not kicking would be the same. And if you swim slower than 1:30.9 per 100m, you should kick. And if you swim faster than 1:16.9 per 100m, you should not kick.
But this would not be necessarily true for all swimmers in all open bodies of water throughout the entire swim. However, it is an interesting study that warrants further investigations for swimmers of all ages, abilities, various swimming techniques and buoyancies (BMI).
It would also be interesting to see how this changes in turbulent conditions in rough seas versus tranquil conditions in a pool for example. The rougher the conditions are, for most swimmers in a turbulent sea, their kick and legs become more of a stabilizing force than a propulsive force.”
Photo shows Avram Iancu from Romania swimming on a 2,860 km stage swim in the Danube River in 2017.
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