The Impact of Dolphin Kicks on a 50-Yard Freestyle Swim

Underwater dolphin kicking is something that is a major part of the sport of swimming. In a sport where every millisecond matters, anything can make a huge impact. From taking an extra stroke to your positioning in the water. So, what impact does taking a couple of extra dolphin kicks have on a 50-yard swim of freestyle?

Firstly, you have all the different types of resistance in the water. The main umbrella that they all fall under is called swim resistance, which is the effects of the water depending on the motion of a swimmer who is in the water. Swim resistance is related closely to drag, which is an element that swimmers are always trying to reduce. Drag is the force that is exerted by a fluid stream on any obstacle in its path. Drag can also be felt by an object moving through a fluid. The resistance met in a forward progression in the water, is called passive drag. Resistance against a swimmer who is exerting a force is called active drag. Frontal resistance occurs when the body is positioned in a way that exposes more of the body’s surface to the water, which will then increase the water-resistive forces. The drag created when the body along with the swimsuit pass through the water, is called skin friction. When front crawl is executed, a vortex or whirlpool will form at the surface. If the swimmer has a bad stroke execution, then the vortex remains and will accumulate around the body, which will then increase water resistance. This type of water resistance is called eddie resistance. (swimming resistance)

To understand how underwater dolphin kicking became popular, a brief history is needed. It is said that the dolphin kick was invented in the earlier decades of the 1900’s, but no one knows for sure who invented the kick. At the time the only strokes that existed were freestyle, backstroke, and breaststroke. Butterfly wouldn't be around till 1952. No one used the dolphin kick during freestyle or backstroke since flutter kick was faster than dolphin kick. In the early 1950’s it was discovered that breaking the surface of the water actually increased friction, which would then slow down the swimmer. This lead breaststrokers to swim underwater for as long as possible. After a year breaststrokers were limited to only one pull and one kick off of each start and turn to counter the staying underwater for as long as possible. (Madge, R.)

In the late 1970’s American Jesse Vassallo began doing a few dolphin kicks underwater off the start and turns. But it was to avoid the waves from the larger swimmers around him and to stabilize his body, not to increase speed. In the 1984 Olympics Japaneese swimmer, Daichi Suzuki went around 25 meters underwater after the start in the 100-meter men’s backstroke. By the 1988 Olympics, five out of the eight finalists for the men’s 100 backstroke even went a minimum of 25 meters underwater off the start. A little while later, FINA, the international swim federation, made the maximum distance that can be swum underwater for backstroke to 10 meters, for health and safety reasons. In 1991, FINA move the maximum distance that can be swam underwater to 15 meters for backstroke. It wasn’t until the 1990s that underwater dolphin kicking for freestyle and butterfly became commonly used. So, in 1998 FINA also applied the 15-meter rule to butterfly and freestyle. (Madge, R.)

Now, onto the science behind underwater dolphin kicks. Underwater dolphin kicking is known as the fastest form of swimming. From a dive, or push off a wall, the kick is meant to carry speed and not generate speed. This is because the purpose of the kick is to delay the process of slowing down underwater. The more underwater you are the less drag coefficient there is. The drag coefficient in the drag force defined by irrespective of the shape of the body. The drag coefficient levels off at 2.0 meters to 2.5 meters. There is five times the drag on the surface when compared to ~1 meter underwater. A tight streamline helps to minimize the amount of the water’s resistive force. The size and speed of the kicks are also important. Powerful kicks will offset the water’s resistive forces. Lager kicks are more powerful but will create more water resistance since they can disrupt the laminar layer. Smaller kicks will keep the body in the laminar layer and thus, create less drag. A streamlined body has a smoother laminar layer, producing less drag. Once the laminar layer is broken, turbulence is created, creating more drag. The speed of the kicking is important, the faster the kicking tempo, the higher the net streamline force. ( Parks, G. & Mark) (Madge, R.)

There are many other examples of how science has influenced the sport of swimming. A great example is the s-stroke. The s-stroke is when the arm pulls diagonally across the body, then sweeps out towards. So, the right hand would be slightly outside the shoulder, the hand sweeps in towards the middle of the body, then back out past the hip in a sweeping motion. The reason this was used, was that it was thought that pull had a greater thrust than a straight pull, straight down from slightly outside your shoulders straight down to your side. But over time, and testing it was discovered that the benefits of the s-stroke are lost since the swimmer has to work harder to execute the stroke compared to a straight pull, which can produce the same trust with a lesser amount of energy. (Wei, Timothy, Mark, Russell, Hutchinson, & Sean)Keeping the body streamlined is also very important. This means your whole body, along with your head, is aligned with your spine, which helps to keep the body horizontal in the water. Reducing drag overall. (Wei, Timothy, Mark, Russell, Hutchinson, & Sean)

There are many parts of the body that are used to complete the kick. One of the most parts of the body for dolphin kicking is the feet. Almost 90% of the thrust is generated beyond the ankle. This is why the bigger and flatter the feet the better they are for dolphin kicking. Ankle flexibility is very important because it allows for the kick to be faster since the motion that the feet go through is similar to a whiplash motion. ( Berkes, H. & Prince, A.) Based on the research and real-life situations, it can be inferred that the number of dolphin kicks done underwater can have an impact on the amount of time it take to swim a race, mostly reducing the amount of time it takes. Concluding, that if more underwater kicks are preformed off of each wall then, it will take less time to complete a 50-yard swim of freestyle.