Biomechanical principles of freestyle swimming arm-pull

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.

Vectors

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.

Motion

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.

Force

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.

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. If power is applied too soon while the arm is in the air, the swimmer will simply strike the water and lose the power. Instead, the swimmer must find the optimal point in their pull where the most water will be moved. This results in the best and most efficient stroke.

There are currently two strokes that swimmers use to optimize their thrust. The first is a traditional pinwheel stroke. This stroke involves keeping the arm straight in the water and producing a semi-circle. The second stroke is known as the caterpillar arm and involves bending the arm slightly to keep a straight line in the water. This second move efficiently pushes more water out of the way and minimizes the strain on the shoulder (Richardson, 1986).

As can be seen, freestyle swimming is as much a science as any other athletic move. It requires precision of motion to counter the force of the water and maximize energy during a swim. Without taking all factors into consideration, an athlete will expend greater amounts of energy with less overall success.