by Marty Hull

The Flutter Kick

One of Swimming's Mysteries

Legs are very powerful on land, able to move us around with quickness and grace. In the water, legs do not always work very well. This article explores how the flutter kick works, why some swimmers have very effective kicks and others do not, and how to make your kick better through specific stretching and strengthening exercises.

The amount of leg power swimmers can transfer to the water depends primarily on the forward range of motion of the foot. The farther your foot bends forward the more leg power you will be able to transfer to the water and the farther you will travel with each stroke. This is why learning how to develop a good kick is so important.

The flutter kicking movement involves alternately separating the legs and then drawing them back together. The moment the legs separate, the surface of the legs encounter drag from the water which slows the swimmer. When the legs are drawn back together, they produce a force which tends to push the swimmer forward. If the kick produces considerably more forward force than it causes drag, the kick will be propulsive.

Individual differences in foot range of motion determine how propulsive a kick is. A (poor) kick that produces little or no propulsion is of little use. A moderately propulsive (fair) kick will work well when sprinting but not as well on longer swims. A very propulsive (great) kick is worth using a lot. This swimmer will appear to flow almost effortlessly through the water when swimming.

Poor Kick: If your foot flexes to less than 90 degrees, it is necessary to bend at the knees to get the foot to an angle that will push you forward. Bending at the knees causes enough additional drag to cancel out the forward force produced by the kick. For the amount of effort kicking takes, this kick is not worth using.

Fair Kick: If your foot flexes to 90 degrees or slightly more, you will have a moderately propulsive kick. The knee must bend a little to make the kick work but it provides enough propulsion to be worthwhile using. For this swimmer, it is often necessary to keep the calf muscle contracted so the foot flexes forward far enough to produce maximum propulsion. This may result in cramping in the calf, but it lets you go faster. It works best for sprints and is less effective for longer swims.

Great Kick: If your foot flexes to significantly more than 90 degrees, very little knee bend is needed to kick. As the foot kicks against the water, the pressure from the water against the top of the foot keeps the foot flexed forward. The calf muscles need not be used. The blood flow which would have gone to the calf muscles is then free to be used in the upper body. This kick causes very little drag and generates excellent propulsion.

Foot range of motion can be increased through stretching. For each degree you gain past 90 degrees, the amount of forward force you produce with each kicking movement increases and the effort required to kick decreases. In essence, you get more propulsion for less work. The swimmer with great plantar flexion may not only go faster, he/she may not even be working quite as hard. Life is not always fair.

Ankle Stretching

Swimmers have been stretching ankles for a long time. I used to stretch mine by bending them under a couch. World record holder Jeff Rouse uses his body weight (photo #1), rolling back on his feet to stretch. Classical ballet dancers have been using simple boards with straps attached for decades to stretch feet.

There are two areas where stretching is possible: the ankle joint and the joints down farther in the foot, the tarsal-metatarsal joints. These joints are the most difficult to stretch, a limit being reached by many after a fairly small improvement. Stretching the tarsal-meta-tarsal joints allows the bottom portion of the foot to move to a better position, further improving the kick.

Stretching Exercises

Ankle joint: Soak ankles and feet in hot water (108 to 118 degrees Fahrenheit) for several minutes. Adjust the strap on a board so that it fits snugly over instep. Sit on foot and slowly slide the board away from you by straightening the leg. This will begin to stretch the joint. The more force you use to straighten the leg, the more stretching force you will put on the joint. Begin gradually, using low force. Stretch each foot for 45 seconds to one minute. Stretch every other day. Gradually, over a period of several weeks, increase the amount of time per foot, the force levels and the number of days per week.

For the first couple of weeks, you will have some tenderness on the underside of the ankle joint. After this passes, you can significantly increase stretching force and duration.

Tarsal-metatarsal stretch: Place foot in the strap attatched to a board so the strap runs over the lower portion of the foot, just above the toes. It is usually necessary to tighten the strap a little. Stretch this area the same way you stretched the ankle joint.

Once you increase ankle range of motion, your kick will change. You will kick with a straighter leg and your foot will move up and down a shorter distance but will move faster. This new kicking movement greatly increases the use of hip flexor muscles. Specific stretching and strengthening exercises are needed to help the hip flexor muscles stand up at this increased demand.

Hip flexor stretch: Place your left leg on a chair (photo #4) while supporting yourself with a hand on the chair back. To stretch, bend the right knee, allowing your body weight to press down on your right leg. As you press down, also lean your torso back. This places excellent stretching forces on the hip flexor muscles.

Move into this stretch gradually so you do not injure or pull any portions of the muscles being stretched. Hold this position 60 to 90 seconds per leg. Do both legs. Do three to four times per week.

Hip Flexor Strengthening

In the deep end of the pool, kick (with fins) in a vertical position. Warm up with a couple of minutes of easy kicking. Then, kick hard for 30 seconds followed by a 20 second rest. Keep you legs straight while kicking. This isolates the hip flexor muscles. You will feel the muscles working in the front of your pelvis. If you allow the knees to bend, the hip flexors work less and the quadriceps muscles work more. Try kicking both ways and you will notice the difference. Begin with 1 x 30- or 2 x 30-second kicking periods with rests in between. Over a period of several weeks, work up to eight to 10 periods of 30-second versicle kicking. Do this three times per week.

When will you improve? This often depends on the range of motion of your foot when you begin. Many swimmers notice some benefits within one to two weeks. If you stretch aggressively and regularly, you will improve for many weeks. The versicle kicking exercises will start to pay off in two to three weeks.

Marty Hull is a top Masters swimmer and a consultant to the Stanford University Swim Team.