Can a swimsuit make you swim faster?

If you've ever tried to race across the pool and found yourself panting, you know it's hard to swim fast. What makes it so hard?水, with its invisible fluid forces, slows you down, says Stephen Wilkinson, a fluid mechanics engineer atNASA. So many fluid forces push against your motion that they're collectively calleddrag.

The strongest force pushing you backward ispressure drag(orform drag). As you push on the water, the water pushes back. If you're not a swimmer, you can get a sense of pressure drag by sticking your hand out of a car's window, with your palm vertical to the wind. The wind will push your palm backward.

More drag acts on you if you swim at the surface, as opposed to underwater. You displace some water, which travels as a wave in front of you. "While you are constantly trying to get in front of the wave, because of the physics of the problem, you never will -- you can't go fast enough," says Wilkinson. The wall of water, calledwave drag, adds to the pressure pushing you backward. The lower you float, the higher the wall, and the worse your wave drag.

A weaker, but weirder, force isviscous drag(also calledfriction dragorskin friction drag). As you swim, a sheet of water sticks to your body and moves with you. Farther away, the water is still. The still water pulls on the water attached to you, slowing you down. What's worse, as you rip yourself and your sheet of water away from the still water, you createeddies. The eddies travel in a few-centimeter halo around your body, called theboundary layer. Those eddies slow you down even more. Viscous drag worsens with the amount of surface area you have in contact with the water and with how well water sticks to you.

If your surface is rough, a type of viscous drag Wilkinson callsroughness dragalso slows you down. It's hard to run your fingers through a shaggy carpet, hard for wind to blow between trees and also hard for water to flow between your body hairs. The water snags on you and slows your swimming.

It seems like a losing battle. Each time you swim a little faster, your drag increases. How, then, do fast swimmers do it?

You can control the watery tumult sloshing between you and the finish line without a special swimsuit in a few ways.

You can lower pressure drag by controlling how you present yourself to the water, saysNASAengineer Wilkinson. It's really your vertical surfaces -- that is, those perpendicular to your swimming -- that push thewater. If you dive in sleekly, keep your body in a horizontal line as you swim and don't allow your legs to sag, you've done a lot to reduce pressure drag. The water will push hard only on your head, shoulders, fingertips and feet.

You can cut wave drag starting with your dive. "You'll notice that when swimmers jump off a block, they spend an awfully long time underwater," says Wilkinson. "Underwater, they have much lower drag because there's no surface wave associated with it. So they'll try to get halfway across the pool before they come up." Once you pop up, if you float higher in the water, you'll push up a smaller wave in front of you. "Naturally talented swimmers seem to float better," says Jeremy Kipp, an assistant swimming coach at the University of Southern California.

Beyond that, get out the shaving kit. Shaving your body hair cuts drag by smoothing your surface. With less roughness, water will flow over you more easily. (Unless you're Mark Spitz; then you manage to win seven Olympic gold medals with water riffling through your mustache.)

Of course, you can also hit the gym. Strong abdominalmuscleswill help you stay straighter and float higher in the water, says Kipp. With a strong upper body, you can worry less about drag -- you'll compensate with more powerful strokes.

But if your technique and your body are in top form and you still want to swim faster, then someone wants to sell you a swimsuit.

The concept of a "fast" suit relies on some assumptions. First, it assumes that your swimsuit can not only cover you without adding to your drag, but that it can reduce your drag. Second, it assumes that the drag-reducing features on your suit will help you swim more quickly, without making you use more energy or oxygen.

The international governing body for swimming, FINA (or Federation Internationale de Natation), approved the first full-body suits that claimed to reduce drag in time for the 2000 Olympic trials [source:Longman]. Swimmers sported various body and leg suits at the 2000 and 2004 Olympics, culminating with Speedo's LZR Racer in 2008. Speedo claims that this is the fastest suit on the market.

该诉讼是织成一张氨纶,”very, very smooth" gray panels sealed onto the torso, legs and rear, says Jason Rance, former head of Speedo's research and design unit, and one of the LZR Racer's designers.

The LZR Racer is smoother than hairy or shaven skin, one reason why Speedo says it's advantageous to squeeze into the suit rather than to swim in briefs. The smoothness comes from the materials; Speedo's woven spandex has a "flatter structure" than knitted material, and the panels, which were optimized inNASAwind tunnels, are like "Glad wrap," says Rance. To make the suit smoother, Speedo constructed it from three pieces of fabric to minimize seams and welded, rather than sewed, the pieces together. Welding cut viscous drag by 6 percent as compared to sewing, says Rance.

It's not only the suit material that Speedo tried to smooth, but the swimmer. Swimmers aren't built like torpedoes, but like bumpy human beings. The curves of their frames andmusclesadd to pressure drag, which is even worse than friction on a rough suit. And in churned-upwater, even the buffest swimmer's skin and muscles shimmy, adding to pressure drag.

Speedo tried to "smooth a swimmer's lumps and bumps" by making the suit compressive, says Rance. The tightness takes getting used to. Speedo tested swimmers' oxygen use in the suit partly to make sure they didn't "build up so much compression that the swimmer can't breathe effectively," says Rance. The company found that swimmers do breathe normally in the suit.

The LZR Racer also squeezes with what Speedo calls a "core stabilizer"-- a girdle where the material is doubled up. Swimmers use their coremusclesto find the posture in thewater教练说,这帮助他们最好的浮动Kipp。”The stabilizer will help you find your balance easier," he says. The stabilizer also reminds swimmers to engage their abdominal muscles during long races, when after 2 to 3 minutes, the muscles tire.

For all its coverage and squeezing, the LZR Racer remains light. Speedo's spandex weighs 100 grams per square meter, four times less than standard swimsuit material [source:Rance]. The spandex is also coated with a water-repellent substance, so it doesn't retain water, making it lighter. Rance emphasizes that the suit doesn't increase buoyancy but also doesn't make swimmers sink.

In simulated race conditions, swimmers swam a start, a 10-meter freestyle and a turn dressed in the LZR Racer and in normal training suits. They swam 4 percent faster and used 5 percent less oxygen in the LZR Racer, says Rance. So presumably, they didn't swim faster because they worked harder. It was because of reduced drag, says Rance.

Something strange happened with swimming records in 2008. Joel Stager, a professor of kinesiology at Indiana University, Bloomington, ran a statistical study on swimming world records since the 1970s. The number of world records broken has gently curved upward, and record times have gently curved downward, but both are reaching plateaus, as expected.

The year 2008 was a curve-cracking anomaly. More than 40 records were set in 2008, double the average for the last 30 years. The fastest men in the 100-meter freestyle at the Beijing Olympics swam, on average, almost four standard deviations faster than predictions.

Swimmers set significantly more records in February and March 2008 than during those months in the past 30 years. Speedo introduced the LZR Racer in February 2008. The statistics weren't out of the ordinary in previous years, when other fast suits were introduced [source:Stager].

"Coaches are better. There's more video feedback. But the suit is really the only thing that has changed," says Kipp.

Speedo's Jason Rance cites improvements in training methods such as high-altitude conditioning, more specialized centers worldwide dedicated to training and more swimmers who swim full-time. "It's a combination of factors, of which the LZR Racer has been one," he says.

Stager pulled a case study from Japan. In April 2008, at the Japan Olympic trials, no swimmers wore LZR Racers. Two months later, at the Japan Open, swimmers competed in LZR Racers in the same pool. Swimmers swam significantly faster at the Open, although they were presumably trying for faster times at the trials. Strangely, sprinters improved significantly more than distance swimmers.

Data like these support -- but far from prove -- that the LZR Racer makes swimmers faster. But the data focus on swimmers who are already fast.

"The LZR Racer is the icing on the cake for athletes at the top of their game. It's not going to make you or me into superstars," says Rance. "We always say to children, and more importantly, to their parents, focus on getting your feet into the pool and doing the lengths on the swim team with a coach."

"I wouldn't necessarily go out and play golf with Tiger Woods's clubs," adds coach Kipp. "If you don't learn the basic techniques, and you don't learn how to train, the suits are not going to help you."

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