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发帖数: 19210 | 1 【 以下文字转载自 Swimming 讨论区 】
发信人: ironman2015 (IMMT 2013), 信区: Swimming
标 题: The Flutter Kick, One of Swimming's Mysteries, July 1995
发信站: BBS 未名空间站 (Mon Sep 16 16:22:58 2013, 美东)
The Flutter Kick, One of Swimming's Mysteries, July 1995
http://www.swimmingworldmagazine.com/articles/swimmagazine/arti
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. |
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