Natural forces affect the movements of swimmers in water. And it is often useful to know how these forces act. This knowledge will help swimming teachers and coaches analyze swimming skills and assist them to understand how these forces influence movement, so that they can encourage beginners to be better swimmers or good swimmers to achieve there optimum potential. Biomechanics is the branch of science that is concerned with understanding the relationship between a living body’s structure and function relative to movement.
In this paper the swimming form of the front crawl stroke will be analyzed, which may result in improvement in the following areas: Improving performance Preventing injury Correcting weaknesses Identifying ways to alter human movement patterns “Biomechanics is considered to be the physics of how the body moves. When these physical principles are applied to sports skills it becomes an integrated study between the internal forces produced by the body and the naturally occurring external forces that act on the body as skills are executed (Carr, 1997, p4.)”. Although the final quality of movement will totally depend upon the athlete’s (swimmer’s) ability to integrate both internal forces generated by muscular actions with the external forces of gravity, buoyancy, fiction and mass that are present during swimming. When looking at swimming one must first look at how the human body acts and generates forces in water. “Water is a unique environment.
It possesses qualities that will assist the swimmer, but it also has qualities that will impede the swimmer’s progress through the water. For instance, the water’s density provides a buoyant force for the swimmer, while at the same time providing resistance to the swimmers propulsion (?????, 1995, p42)”. Topics to continue with: Main principles and their application Density Water Resistance Skin/Frictional Resistance Frontal/Wave Resistance Eddy/Turbulence Resistance Propulsion Water Friction Propulsive Drag Lift Force Streamlining The main principles and their application of the front crawl stoke Buoyancy ; Flotation An object that is immersed either totally or partially in water experiences an upward force as the water’s density endeavors to stop it from sinking (Maglischo, 1982). This upward force is known as the buoyant force and acts through the center of the displaced water. This force therefore, tends to counteract the effect of gravity and the weight of the object, the net result being that the weight of the object is reduced by the upward force of buoyancy (Costill, 1992). (#Diagram#) Every object has an absolute center position where all forces exerted by the body equal zero.
This central point of an object’s mass is known as the center of gravity and is the point around which it balances. “The center of gravity is approximately 50-52% of an individuals height, as there is an equal spread of mass above and below this point (Allen, 1999)”. The same can be said for the center of buoyancy, as above and below this point there is an equal spread of volume of the displaced water (Allen, 1999). The location of the center of buoyancy which is the center of the water displaced by the body, is actually closer to the head than in the location of the center of gravity.
The reasons for this are: The volume of water displaced has a greater mass then the chest area. The chest has a lower density than the water because of its lung capacity. Therefore the upward force of buoyancy acts thought a point higher up the body than the center of gravity (Costill, 1992). (#Diagram#) (I may need to include more?) (And relate it back to the front crawl?) Density The term specific gravity is used to describe the ratio between an object’s density to that of water’s density. “Pure water density being the “reference point” having a specific gravity of 1.00 (Carr, 1997, p67)”. Therefore anything placed in water will float or sink in accordance to it’s own specific gravity value.
Anything greater than 1.00, will sink. While anything less than 1.00 will float. In the human body there is variation from person to person, this is due to the amount of air in ones lungs and the percentage of bone, muscle and fat, which all vary in their own individual masses. Both bone and muscle are heavier than fat. From this information one can assume that a lean and muscular body or one with a heavy bone structure, will not float as well as one that is the opposite.
(Chart #1.) Relationship between Specific Gravity & Body Composition Studies have shown that: “in general, the specific gravity of women will be less than that of men, and that of children will be less than that of adults, especially at ages when the trunk is a greater proportion of the total body mass” (Adrian & Cooper, 1989). (Chart #2.) & (Diagram The human body in water) Water Resistance In all the strokes used in swimming there is resistance. As swimmers move through water, they should aim to minimize resistance. In the front crawl action there are three major forms of resistance they are: Skin, or frictional resistance Frontal or wave resistance Eddy or turbulence resistance. (Diagram of the front crawl resistance) Skin or Frictional Resistance In the action of the front crawl, this form of resistance occurs because “new” water is always rubbing against the swimmer’s body.
One way this could be significantly lowered would be if the body could carry on its surface a very thin layer of surface water. This phenomenon naturally occurs in under water animals such as dolphins and sharks. This is the same type of concept which occurs on golf balls due to the dimpled surface (Wilmore). To improve the resistance in the front crawl action swimmers can try to make their bodies as smooth as possible. Some examples of this are seen in the close fitting swimwear, oiling the skin and shaving the body and head. In the front crawl action the magnitude of the surface friction will be determined by: The speed of water relative to the swimmers speed The amount of surface area of the body The smoothness of the body The qualities of the water (Maglischo, 1982) (#Diagram#) Frontal or Wave Resistance In the action of the front crawl the body is propelled forward through the water.
This creates a wave or wall of water, which swells up in front of the body. “These waves can have a powerful retarding effect and the retardation increases as the swimmer’s velocity increases (?????)”. It should be noted how ever, that this wave also assists in the front crawl action as the swimmer breaths behind the wave formed by the head, thus keeping the head level and beneath the water line. “The net effect being, that swimmers are able to conserve energy and still maintain a streamlined body position throughout the stroke (Costill, 1992, pg.48)”.
The effect of frontal resistance changes continuously according to stroke technique. The difference in depth of the area covered by the body during the action of the front crawl (Maglischo, 1982). (#diagram# Front crawl bow wave) Eddy or Turbulence Resistance “Water left undisturbed will flow evenly and in a laminar state (Maglischo, 1982, pg.12.)”. However, swimmers inevitably disturb the water that they are moving through. This effect can be reduced by keeping the body streamlined, disturbing a minimum quantity of water, thus keeping the water in a laminar state. (#Diagram of Form Drag#) Laminar flow reduces resistance because the water molecules slip past the streamlined body with minimum change in speed and/or direction.
This is not the case if there is an obstruction in the path of the water. In this situation, the water molecules slow down and push against the leading surface thus creating a high pressure in front of the object (Maglischo, 1982). At the same time the water cannot change direction quickly enough behind the object as it moves through the water. This turbulance has a low pressure and is characterised by eddies and moving water (Maglischo, 1982). A good example of this situation is shown by the bow wave in front of the head and the turbulence of water that is behind the head and down the back of swimmers as they move forward through the water in the front crawl. The whirling currents are areas where the water is unstable and the lower pressure area that has been developed will create a suction effect to reduce the forward motion by pulling the body part or parts back.
(#Diagram Eddies around the body#) Eddy turbulance can be caused by poor stroke technique or by having a poor streamlining position in the water. Examples of these errors in the front crawl are: Poor hand and arm entry in the water. Leg kicking with a large knee bend. A deep hollow in the back, which raises the hips too high. (Maglischo, 1982) The human body is not adapted to moving freely through water, due to its large flat areas and rounded limbs.
This leads to turbulence being an unavoidable force in the simming action that is the front crawl. The magnitude of eddy turbulence however will depend upon: The cross sectional width of the body part that is moving perpendicular to the flow of water. The shape of the body parts. The smoothness of the surface.
(Costill, 1992) Streamlining: Reduced resistance. Eddy Turbulence: Suction effect on the back. Pressure on the front pushes the object back. (#Diagram Eddy Resistance ; Eddy Turbulence#) Propulsion Action of the Front Crawl The Arm Stroke Entry ; Stretch Down sweep ; catch The in sweep The upsweep Release ; Recovery Timing of the Arms The Flutter Kick Down beat Up beat Kick Width Lateral Kicks Is the Kick Propulsive? Body Position Horizontal Alignment Lateral Alignment Breathing Timing of the Arms ; Legs 6 Beat kick 2 Beat kick 2 Beat cross over kick 4 beat kick Breathing Patterns 25m – 50m 100m Longer Distances Variations in Style Bibliography Anthony, C.
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