Thursday, August 18, 2011

The Swamp Backstroke: a new swimming stroke with two "gears"

The swamp backstroke is a stealthy, medium-speed swimming stroke propelled solely by underwater movements of the arms and hands. It is particularly suited to shallow water.

I am certainly not the first person to try this method of swimming—which in essence is simply floating on your back and propelling yourself with sculling motions of your hands—but I am coining the name and publishing these observations in the hope of getting more people interested in developing this useful swimming stroke.

The swamp backstroke, in common with other backstrokes, has two familiar characteristics:

breathing is unimpaired,

you can see everything around you, but not where you are going (extreme caution around pool walls and other swimmers is urged.)

The swamp backstroke stroke also has some characteristics which are unique:

only the arms and hands are used for propulsion,

all movements are underwater,

the body stays flat-level in the water with no rocking,

the hands are used continuously as efficient hydrodynamic lifting foils: drag plays no useful role in this stroke,

water as shallow as a wading pool can be successfully navigated,

there is a "low gear" and a "high gear" in the swamp stroke, that is, the best hand movement at high speed is fundamentally different from the best hand movement at low speed.

Swimming the swamp backstroke I have been able to achieve a top speed of about 1m/sec. That's done without heroic effort (I'm 56 and not an athlete.) A competition-level freestyle sprint would be twice as fast, but the swamp stroke uses much less of the body's musculature and is nearly silent. Because propulsion in the swamp backstroke is hydrodynamically efficient, I hold out hope that there is a speed (somewhere below one meter per second) where the swamp backstroke is the most metabolically efficient way to cover long distances. In shallow water at least, that's likely to be true.


This is not a well developed stroke, so will not to try to be specific about my own arm and hand movements, they are probably not optimal anyway. Also, when it comes to rapid underwater movements of the hands, you will find the water has a large say: what you are trying to do isn't exactly what the water makes you do.


I will be specific about keeping your body in a trim position. When floating on your back the natural tendency is to raise your head and let your butt hang down an inch or two. You certainly can do a swamp backstroke in this posture, but it will be like dragging a parachute. You must get your butt up to achieve any speed, and this requires letting your head back, ears in the water, and arching your back slightly.


You can find the hand movements for low-gear by standing in deep water and learning the feel of unseparated hydrodynamic flow over your hands. Palms facing down, move your hands back-and-forth from side-to-side at various angles of attack. The force of the water against your palm can be surprisingly strong. Then, suddenly, at too great an angle of attack, the flow stalls (separates) making the flow over the back of your hand feel bubbly and less dense. Efficient propulsion requires staying in the unseparated, unstalled regime. Experiment standing in deep water till you are satisfied you can produce a strong downward thrust while moving your hands near your hips. Fingers fully extended and held tightly together work best.

Now, do the same hand movement while floating on your back, and you're off!

Steering in the swamp backstroke is accomplished by simply exerting less thrust on one side. See what variations make you go faster. Get comfortable swamping in low-gear—and used to anticipating and avoiding obstacles—before trying to learn high-gear.


The limitation of low-gear is that once you start moving through the water with some speed, the relative direction of the water approaching your hand changes. It soon becomes anatomically impossible to rotate your wrist far enough to stay in the unstalled regime on each sweep of the hand.

Notice that in low-gear the flow over your hand alternates: at alternate times the thumb-side or the pinky-side of your hand forms the leading edge of the airfoil. To achieve higher speed through the water you must transition to a non-alternating flow where the the thumb-side of the hand is always the leading edge. This transition proves easy, but it must be done at speed since the new hand movements would be totally ineffectual, and even nonsensical, in still water.

While swamping at speed, you rotate your hands so that the thumb-side faces the oncoming water. This requires lowering your elbows (which can be a problem in very shallow water.) Keep your hands underwater and place your elbows as deep as possible—that will leave you in a position where your hand is a straight extension of you forearm, the both being inclined about 45 degrees to the water's surface. In that position all pitch rotations of the hand originate at the elbow.

Don't think about what you are going to do, or how it can possibly propel you forward. (As I said, the high-gear movements would be nonsensical in still water.) Concentrate only on doing work against the hydrodynamic lift force on your hands.

Lift is the sideways component of the hydrodynamic force, it is always perpendicular to the direction of the flow, and it is non-dissipative. That means that 100% of the work you do against it goes into increasing the kinetic energy of the flow. In this case, it efficiently moves you forward through the water at a respectable clip.

In my experience, fast, small hand movements near the hips are best. I'll be interested to hear your results.

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