Biomechanical Principles Term Paper

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Biomechanical Priciples

Biomechanical Principles

Biomechanics is the study of mechanical and physics principles in relation to motion in sports. Every sport has its biomechanical theories and each one is specialized to that particular skill with equations derived from Newtonian physics and knowledge of the human body and its capabilities. When combined and properly practiced, biomechanics can improve an athletes overall performance, making the athlete superior to their competitors.

The freestyle arm-pull in swimming is a precise study in the art of biomechanics introduced for an efficient result. It is an established fact that water is 773 times as dense as air and 55 times as viscous (Miller, 1975). What this means is that planning an efficient stroke in water is going to require greater strategy than planning an efficient stroke in air. The primary factors that go into creating the ideal stroke in swimming are vectors, motion, force, work, and power.


The primary vectors in swimming are drag and lift. Drag is the slowing effect that water has against the body's speed. Drag slows the body down and increases the amount of force necessary for an athlete to effectively move through the water. In freestyle swimming, drag is also the greatest factor in allowing a swimmer to pull themselves through the water.

The key technique for taking advantage of drag vectors in water is known as scribing the water. This motion in essence pulls the swimmer through the viscous layers of the water and propels the body through (Richardson, 1986).

While this propulsion does move the swimmer quickly, the swimmer also has additional vectors pulling against the force. There are three specific vectors to consider that pull against the swim stroke and the swimmer. The first vector is friction drag. Friction drag is directly related to the viscosity of a liquid. It is the reason why molasses is thicker and more difficult to stir than water. The way this effects a swimmer is simple, the water that is immediately against the swimmer's body gets pushed into the next layer of water and so on. The less viscous a liquid is, the easier these layers move.

The second vector pulling against swimmers is pressure drag. According to Boone, pressure drag is "The orderly flow over the swimmers' body may separate at a certain point, depending on the shape, size and velocity of the swimmer. Behind the separation point, the flow reverses and may roll up into distinct eddies (vortices). As a result, a pressure differential arises between the front and the rear of the swimmer, resulting in 'pressure drag', which is proportional to the pressure differential times the cross sectional area of the swimmer." (Boone 2005). So, along with the force of each layer of water pulling against the swimmer, the water then comes back and pushes against the lower half of the swimmer's body.

The final form of drag vector is wave drag. Wave drag occurs at the surface of the water. As waves form in the pool, the force of the waves against the body slows the body's progress through water. It is this form of drag that causes the best athletes to spend as much time as possible under the water (Boone).

The primary way that athletes overcome these force vectors is through specialized drag suits. The drag suits are designed to streamline the athlete through the water and reduce the total amount of friction and pressure drag experienced during the swim, thus making the athlete swim faster.


According to Newton's laws, an object will remain in motion once propelled into motion. This principle, also known as inertia, applies to swimming to mean that the more force used to propel the swimmer into the freestyle swim, the less force the swimmer must use to propel themselves once in the water (Burkett 2012). Once the inertia from the dive wears off, the swimmer's propelling motion is the key to the freestyle swimming stroke as it ensures that forward propelling of the swimmer through the water. The irony is that swimmers must pull back with their stroke in order to move forward in the water. This motion, known as angular motion, requires the swimmer to control the movement of their arms and form a semi-circle in the water. The backward pull required by athletes is very straining and uses up a high amount of energy. It is this fact that prompted biomechanics to determine the most efficient motion for the swimmer's body in the water. Keeping a freestyle swimmer in motion in the water requires three different bodily movements. The first is the backward pull stroke with the arms. The second is a slight side-to-side roll in the water, allowing the body to move more freely. The final necessary movement is the kicking of the feet. These three movements combine to keep the swimmer in motion.


Newton proved that every action has an equal an opposite reaction. This is true in freestyle swimming and modern swimmers use this fact to their advantage (Miller, 1975). While freestyle strokes alone will propel the body somewhat, it will also tire out the arms and legs quickly, resulting in a less efficient swim. In order to increase the swim's efficiency, modern freestyle swimmers also use propulsion of the initial dive into the water and the pushing off from the pool's walls to increase their velocity through force.

There are also forces constantly going against the athlete during the swim. The primary force against the athlete is drag, as discussed above. Additionally, buoyancy or lift can also factor as a negative force depending on the swimmer's overall strategy. For instance, it is lift that causes the swimmer to remain toward the top of the water, which is where wave drag is greater.


There is no doubt that the freestyle stroke requires a large amount of work from the swimmer. However, there are biological factors that can play a key role in minimizing the work and leading to reserved energy and a stronger finish. The first factor is correct muscle selection. The freestyle stroke uses more than just the arms to propel. In fact, if just the arms and shoulders were used, the athlete would get tired very quickly and could also sustain serious shoulder damage. Instead, the primary muscles used for good strategy include the trapezius in the back and the abdominal. The trapezius moves the shoulders in a greater circle than other muscles, allowing for a fuller and stronger range of motion. The abdominal muscles press the legs into a larger "V" kick than the legs could otherwise do. Both of these sets of muscles are among the strongest in the body, making use of them is more efficient calorie for calorie (Richardson, 1986).

The second issue in the water is stability. Core muscles play a vital role in stabilizing the swimmer and ensuring the proper motion and roll within the water. Without stability, force is lost, resulting in greater expenditure of energy or more work for the athlete in the stroke.

Finally, angles play a large role within the water. Before a race commences, athletes are encouraged to take practice laps in the pool. The reason for this is to feel the overall water and determine the optimal angles for their swim. If the angle of the stroke is too shallow, then the swimmer will have to pull harder on the water to propel. If the stroke is too short, then more strokes will be required, leading to muscle fatigue. So, an ideal angle for both the arms and legs must be found.

Power or Thrust

The final mechanical principle in an effective stroke is power. freestyle swimmers must choose where and when to apply power to their stroke and how to angle their bodies to maximize the stroke.…

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