Streamline (swimming)

Streamline form is a swimming technique that is used underwater in every stroke. At the start of a race or on a turn, streamline form is used, usually along with a dolphin kick or flutter kick, to create the least amount of resistance to help the swimmer propel as far as they can. Many factors contribute to the perfect streamline form and mastering this method increases a swimmer’s speed. Streamline is one of the key fundamentals to mastering any stroke.

The streamline position consists of a person placing hand over hand, fingers over fingers and raising their arms above their head so the biceps are tucked close to the ears. The belly is sucked back to decrease curvature of the spine in the lower back and the swimmer’s head is brought back to ensure that neck is in line with the spine Pinching the shoulder blades together is helpful in aligning the spine to straighten out the back. Legs are straight and feet are pointed. In theory, a perfect, straight line will be made down the backside of a swimmer from their head to their feet. The body should be on a horizontal plane under the water, with the legs kicking straight from the thighs and hips, not the knees. A great deal of flexibility is usually needed to reach the goal of a perfect streamline, particularly flexibility of the shoulders. Kicking in the streamline position underwater can be substantially faster than swimming any of the other aquatic strokes, competitive or otherwise. For this reason, competitive swimmers often try to kick in a streamline position off a wall or the starting block for as long as they can be underwater before coming up for their first stroke. This is why many swimmers spend a lot of time perfecting the form and technique of streamline.

There are three main resistances caused by drag on a swimmer which are caused from friction, form, and wave-making forces. The most detrimental force to streamline would be the resistance caused by form. Bad form will cause more drag on a body in water (resistance) resulting in more work needing to be done to cover the same amount of distance. The amount of resistance on an object can be determined by the formula,

D is the constant for the viscosity of the fluid, p is the density of the water, A is the surface area of the body traveling through the water, and v is the velocity of the body.

Because the velocity is squared, the resistance will be exponentially affected by the value of velocity, which is why it is important to minimize the surface area as much as possible. Minimizing surface area is directly proportional to technique. Timing in the transition from the glide to the kick is crucial for a swimmer to keep up their momentum. Switching to the kick too early will cause an increase in resistance. A transition that is performed too late will result in loss of speed due to the decrease in momentum, resulting in a waste of energy while returning to race speed. With all aspects of streamline brought together, it makes it the most hydrodynamic position one can assume in the water.

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