Despite its name, the dolphin kick—the motion that propels the swimmer forward underwater after he dives in and at the turns—isn't just about the legs. It requires a swimmer's entire body to crack like a whip, creating a fluid wave that starts at the chest and increases in amplitude as it travels all the way through the toes. In the best swimmers, this wave moves at about nine feet every second, about half the speed an actual dolphin performs the same motion. To move this quickly, whole-body flexibility is key. Twenty-time world record holder Michael Phelps ripples two waves down his unusually long, flexible torso at a time—cracking the whip in his body twice as often as his competition. Since the kick moves swimmers far faster than any surface stroke (there's less resistance underwater), perfecting it can give Phelps a big advantage off the gate. So why not just stay down there the whole race? After the 1988 Olympics, the world's governing body of swimming, FINA, restricted it to the first 15 meters after a start or turn.
"The dolphin kick is going to be used as a weapon in Beijing," says Russell Mark, biomechanist manager of the US national swim team. During the last four years, Mark says the best American swimmers, including Phelps, have been especially focused on honing the technique. Engineers at George Washington University studying fluid dynamics recently calculated that more than 75 percent of the propulsive force of the dolphin kick comes from snapping the ankle. "If you have the ability to flip your ankle like a ballet dancer, you'll get more whiplash action," says Rajat Mittal, who has consulted with USA Swimming. The elite swimmers they've studied can bend their ankles beyond that of a ballerina's pointed toe.
Below: By cracking one's body like a whip, the dolphin kick can move swimmers far faster than any surface stroke.
Well, i guess it helps MP that he wears a size 50. (Yes, I'm en europe)
"(there’s less resistance underwater)"
I don't get it. Isn't there less resistance from air? I mean, drop a penny in a 6 ft. deep pool or drop a penny from a 6 ft. height. Won't the penny you drop from 6 ft. hit the ground first, presumably because of less resistance.
"(there’s less resistance underwater)"
This is demonstratively preposterous, with all due apologies to <i> Popular Science. </i>Any bit of experimentation will quickly show the falsity of the quotation above. Next time you are in the bath tub, put your hand in the water and move it. Now do so in the air. Which is easier to do? In which does one's hand move faster? Not only that, let's look at real world times. If there is less resistance in water than in air, one should be able to swim faster than one can run. César Cielo, I believe, holds the current record for the 100m freestyle at 46.91 seconds. The fastest sprint for 100m is something around 10 seconds, or about 4-1/2 times faster.
The reason the dolphin kick is faster than traveling in air when swimming is the swimmer can bring more force against the water than other foot strokes and the water provides more resistance (not less), thus allowing the push to achieve more. One can push against a wall, which has a great deal of resistance, and achieve a much greater reaction than if one pushes against air. Try it. Sit in a chair with wheels and push yourself away from a wall. Now push away from nothing but air. Which one moved you further? Thus, the truth is the dolphin kick works because of more resistance "down there," not less.
Because the kick involves using more muscles to push against the water and the water provides greater resistance than air to push against, the kick can achieve greater results. Additionally, the kick can provide forward motion with both the up and the down strokes, while the frog kick, the one used for the breaststroke, only achieves force against the water when bringing the legs together, but not when separating them, thus frog kick has considerable recovery time that limits its maximum results.
Most people get into trouble with the butterfly because they lift their way up heads to breath, thereby pushing their torso, mostly their butt, down and, therefore, presenting a greater surface area to the water. The greater the surface area presented, the slower one moves in water with the same amount of propulsion. The trick is to keep one's body parallel with the surface of the water or, even better, having more of the plain of one's body in air (which will over far lesser resistance to the forward motion of the body). The Australian crawl, the stroke most used in the freestyle (one may swim any style in the freestyle, hence the name), is the most efficient at keeping one's body parallel to the surface of the water, presents the smallest plane against the water, and provides the greatest combination of propulsive force. While the dolphin kick alone is better than the flutter motion in the crawl, the motion of the arms cannot easily be combined with the dolphin kick, so the flutter kick is used. If you want to swim a good butterfly, use the force of your arm stroke to lift your torso partially from the water, thereby presenting the smallest possible plane to the water, and lift the head only enough for the mouth to clear the surface to breath. The face should remain face down, but rise above the water about half an inch, more than enough to take in enough air for the short distances one swims the butterfly (notice no one swims the butterfly in distance races; it is not only slower overall than the crawl, but it requires far more energy to accomplish, not a good combination for swimming 10,000 meters).
Less resistance in water than air?!?! Nonsense.
Both of you misread the article. It said there is less resistance underwater vice a surface stroke. Which is true. If you're talking about air, you are correct. If you're talking about the surface of the water, you are incorrect. And, no one swims in air.
When you swim on the surface of the water you make lots of waves. Those waves are wasted energy. However, when they dolphin kick underwater they generate very small to insignificant amount of surface waves.
While you spent a good deal of energy explaining why your hypothesis is correct, the author is indeed correct.
(A interesting note is that submarines require substantially less energy for the same displacement as a surface vessel.)
Alkelaun, you are giving the author of the article the benefit of your own knowledge. The author plainly stated that there is less resistance underwater and didn't say anything about waves being wasted energy. I don't think I misread the article, I think the author was careless.
the author was in no way careless he clearly states
"Since the kick moves swimmers far faster than any surface stroke (there’s less resistance underwater)"
which clearly implies that the resistance is less compared to being on the surface (not floating in mid-air) quite understandable and, to me, quite intuitive.
also i would think the surface tension of the water could increase the resistance on the surface stroke
dude you should be way less confident in your own opinion don't state everything as though you have personally tested this using proper scientific methodologies and published your results... if you have actually done some original research and would care to share it with the community that would be really helpful to further our understanding
"the dolphin kick is faster than traveling in air when swimming"
i have never managed to swim in the air, unless you mean faster than swimming on the surface
"the swimmer can bring more force against the water than other foot strokes and the water provides more resistance (not less)"
this is complete conjecture your "evidence" is to "put your hand in the water and move it. Now do so in the air. Which is easier to do?" well obviously the air... hows about next time you go swimming push off from the wall underwater with your arms straight out without kicking then try the same but on the surface and see which one allows you to travel further, i'm sure you will find underwater allows you to travel the furthest and since the initial impulse should be about the same i think this is valid enough to demonstrate that the author and the science behind the article are correct
P.S this is only MY opinion based on my ability to swim without drowning and my intuition, next time i go swimming i plan to test my theory