Hate kick sets? Loathe the fact your legs feel like they’ve caught on fire during fast freestyle? You’re not alone in thinking that the act of kicking may not be all it’s cracked up to be. By recently studying athletes in a flume (resistance pool) swimming freestyle at different levels and speeds, researchers at University of Tsukuba and the Tokyo Institute of Technology scientifically determined that kicking may bring no benefit when trying to swim freestyle faster.
Published in the Journal of Biomechanics this summer, the Japanese study found that kicking water indeed provided a propulsive force when swimming at a relatively low speed of 1.1m per second, or 1:30.91/100m. However, when the swimming speed increased to 1.3m per second, or 1:06.92/100m, the leg movements ‘hampered water flow and produced resistance equivalent to the cube of the speed ratio.’
As such, they determined that while kicking is the primary action that enables swimmers to keep a horizontal body position in freestyle, leg movements can generate significant resistance when swimming speed exceeds a certain level. Per the Journal, ‘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.’
Below is one table from the full report, displaying how the drag coefficient increases in whole stroke freestyle as the speed of the these particular subjects increased.
Graphic courtesy of Science Direct.
Hideki Takagi, a sports engineering professor at the University of Tsukuba, said, “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.”
You can read the study from the Journal of Biomechanics in its entirety here.
It is not the meat. Nor is it the motion. All legs and feet as well as all kicks and flopping are not created equally. But, in the end, it is none of that.
Rather, it is FLEXIBILITY.
IMNSHO, the connection to propulsion hinges upon FLEXIBILITY.
(Did you love that pun too?)
I know this is probably referring to a common stationary speed, but there has to be a difference when applied to a race and the distance of the race. There is a threshold where the amount of oxygen moving your legs requires meets the amount of oxygen the rest of your body needs and a fine line between the balance of the two. Obviously a perfect tight technique at full blast over the course of a 1500 will make you faster…. but using your legs requires more oxygen. Thus why many people can “pull” a 500, 1000 or 1500 faster than they can “swim” one. It’s a balance…. pure and simple. This study is pure aerodynamics and does not consider… Read more »
If they didn’t control for ankle flexibility, this study is rubbish.
“Determined that kicking may…”.
Discussing kicking while on the surface of the water may be a moot point, however, underwater dolphin kicks off the walls will ALWAYS be faster (than not kicking), and significantly so 🙂 Conclusion: kicking is still relevant and necessary if you would like to swim FAST!
I was their test subject, when I kick, I go backwards.
Sounds like a great time for an A/B test. I think the rest of the world should follow this science and the US do what we normally do; big underwaters and tons of kicking.
I presented my thesis on Bio Mechanics involved in Competitive Freestyle, Starts & Turns during my Graduation in Swimming at Sports Authority of India, Bengaluru during the year 1999 – 2000. According my study, Buoyancy of the swimmer plays a major role in competitive swimming and almost 30% of the speed is generated by kicks in Freestyle. Also kicks help the swimmers aligning their body in a straight line.