Most swimmers, down deep, really do suspect their legs don't help them out much in the speed department. But because the kick obviously pushes them forward to some degree, they don't dare gamble on not doing kicking sets. Besides, the fastest swimmers in any group or on any team usually also seem to be the fastest when the kickboards are handed out. So they must know something, right?

In fact, your kick does contribute something to propulsion, but not in the way most of us imagine. My sense is that most people vaguely think they need a good kick because either:

1. If my arms can propel my body at 4 feet per second and my legs can propel it at 2 feet per second, maybe together they can propel it at 6 feet per second.
2. If I really work hard at those kickboard-training sets, I'll get a more powerful "outboard motor," say a 40-horsepower Evinrude instead of the 20-hp model one I have when I don't train hard with a kickboard.

But it doesn't pan out quite that way. Yes, a swimmer kicking on a board creates propulsion, sometimes even really fast propulsion. The best kickers in the world can go one minute or faster for 100 yards on a kickboard, faster than most of us can swim. But that tells us nothing about how much a stronger kick adds to whole-stroke swimming, nor the energy cost of whatever good it does do.

Over 50 years ago Doc Counsilman, the legendary Indiana University coaching legend, designed an experiment to actually measure what kicking adds to propulsion. He devised an apparatus to tow swimmers in a glide position at various speeds, both kicking and without kicking. Tension on the line was measured to see if it was greater, the same as, or less, when kicking than it was just gliding along.

The only instance in which kicking decreased tension on the line (i.e. added propulsion) was at slow towing speeds, with the swimmer kicking at maximum effort. But at any speed over 5 feet per second (1:00 per 100 yards) the kick contributed nothing and, in some instances, actually increased drag!

Counsilman interpreted these results using an automotive metaphor. Imagine, he suggested, a car with separate front- and rear-wheel drive. If the front wheels turn at 30 mph, but the rear wheels turn at 20 mph, the car's total speed will be not 50 but less than 30 mph, because the rear wheels create drag. The same thing happens, he contended, when a swimmer with a reasonably fast upper body persists in emphasizing a less-efficient kick. The kick consumes energy and creates drag. More work, less speed.

How much energy the kick costs has also been measured. Several different studies over the past 30 years have gauged the oxygen consumption of competitive swimmers while pulling only, kicking only, and swimming whole-stroke. Each study found that hard kicking greatly increases the energy cost of moving at a given speed. In one study, kicking at a speed of about 60 seconds for 50 yards--a rather moderate speed for any competitive swimmer—used four times as much oxygen as pulling at the same speed.

The obvious conclusion: Kicking can add only a modest amount of propulsion to an efficient stroke, while it can add a significant amount of drag and enormously increase the energy cost of whole-stroke swimming, if overemphasized. Therefore swimmers should do all they can to maximize the benefit of their kicking while minimizing the work they put into it.

Kick For Efficiency, Not for Speed
"Fine," you say. "If all kicking does is burn energy and cause drag, why bother to kick at all?" Well, because that's not all kicking does. An efficient kick will improve your stroke and, in fact, is essential for the kinetic chain to produce anything like the power it's capable of producing for you.

To understand this, you have only to imagine a baseball pitcher trying to throw a fastball with his legs shackled. Or Venus Williams trying to hit a tennis serve without being allowed to step into it. Or you, trying to swoop and soar on a playground swing while holding your legs tucked tightly under you.

The key is to allow your legs to move in the most natural, efficient way while avoiding non-essential movement. An efficient, impeccably timed kick can make the action of the kinetic chain far more potent, and cost very little energy. Skeptical? Stand with your feet a bit more than hip-width apart, arms hanging loosely, with room to swing them freely. Keeping your feet flat on the floor, rotate your body right and left, letting your arms swing out freely as you do. You'll feel the relatively rigid, fixed position of your legs impeding your movement, creating tension from your knees to your hips.

Now repeat the movement, but allow your back heel to lift as you swing. You'll find that you rotate freely at least an additional 30 degrees in each direction, and eliminate the inhibiting tension.

Repeat the experiment one last time, but now add just a little push off the ball of the rear foot whenever it feels most natural to do so. When you time this gentle push correctly to the body swing, you'll feel yourself rotate with even more speed and power.

Just for fun before you quit, try the same rotation/swing while fluttering your feet rapidly in place. See what happens? Right. Your coordination and efficiency break down and the movement degenerates into a sloppy, shapeless mess. Uncoordinated leg movements always scuttle the rhythmic, driving momentum you can create when your legs and torso move with great coordination.

And that shows precisely what can happen when an efficient kick coordinates well with great body rotation—both long-axis and short-axis. It also shows what can happen with an inefficient kick—no matter how well conditioned it may have become through miles of diligent kickboard training. The inefficient kick will be very good at adding drag and energy cost and contributing nothing to propulsion or speed. And it will be very good as well at making you much more tired, much more quickly. For that final, uncoordinated twitching I suggested you try above is exactly what happens to an unbalanced swimmer. They sense their legs are sinking, and react by moving them even more frantically. The uncoordinated kick that results not only fails to correct poor balance, it destroys any possibility of smooth, fluid body rotation. And it needn't happen at all to a swimmer who has truly mastered balance, for a balanced swimmer's legs are freed of having to kick this way and can move freely. When they do, they can find the movement pattern that coordinates best with body movement.

The first example above-swinging with feet flat and fixed-is equivalent to a swimmer trying not to kick (or perhaps wearing a pull buoy). Legs held rigidly in place will add tension or torque that impedes the free rotation of the body, and muscle tension is nothing more than work with no benefit. The free-heel movement is the equivalent of a natural, non-overt, 2-beat kick, moving in coordination with body roll. This kind of kick feels effortless, almost unconscious, and is the best for most people when swimming longer distances or when doing fitness or lap swimming. The third example, adding a well-timed push to your body swing, is the equivalent of putting a bit more snap into the downbeat of your 2-beat kick. If you add it at just the right time and put in just the right additional amount, you'll feel your hips drive with more power. And if you keep your armstroke connected to body roll as you're supposed to, increased hip drive will translate, finally, into a more powerful stroke.

But it's critical that you first establish impeccable timing in your 2-beat kick, and that you can sense where to add the extra snap just as easily as you can while standing in the middle of the room and swinging back and forth.