Swimming Science: Optimizing Training and Performance - Hardcover

Hardcover

ISBN 10: 022628784X ISBN 13: 9780226287843

Publisher: University of Chicago Press, 2018

Synopsis

Swimming is often touted as one of the most accessible workouts—low impact, low tech, and beneficial at any stage of life. Yet each time you suit up and dive in, your body’s moving parts must work together to propel you through dozens of pounds of water resistance, somehow emulating the movements of species that evolved specifically for the water. What are the physical forces at work when you get in a pool, and what determines whether you will sink or swim?

Writing to competitive and novice swimmers alike, contributors to this volume break down every aspect of the sport. Swimming Science covers physiology, psychology, and safety, as well as hydrodynamics, nutrition, and technique. Each chapter examines these topics through a series of practical questions. What are the forces acting on you when you swim, and how do your muscles best generate propulsion against those forces? How much protein, salt, and iron should a swimmer consume, and how does energy from carbohydrates compare to energy from fats? How important is the “swimmer’s physique” in competitive swimming, and is technique or strength more necessary for generating speed? These questions are examined with the aid of explanatory diagrams and illustrations, and the book can be used to search for particular topics, or read straight through for a comprehensive overview.

Whether you are a competitive swimmer looking to optimize your performance or just beginning to dip a toe into the sport, Swimming Science is a must-read.
 

About this title

About the Author

G. John Mullen is the CEO of COR Physical Therapy and Personal Training in Santa Clara, CA. He is also the founder of the blog Swimming Science and a regular contributor to Swimming World Magazine. 
 

Excerpt. © Reprinted by permission. All rights reserved.

Swimming Science

Optimizing Training And Performance

By G. John Mullen

The University of Chicago Press

Copyright © 2018 Quarto Publishing plc
All rights reserved.

ISBN: 978-0-226-28784-3

Contents

Introduction, 
CHAPTER ONE hydrodynamics Tiago M. Barbosa, 
CHAPTER TWO technique Rod Havriluk, 
CHAPTER THREE pool training Rod Havriluk, 
CHAPTER FOUR dryland training Allan Phillips, 
CHAPTER FIVE nutrition Kevin Iwasa-Madge, 
CHAPTER SIX injury prevention and rehabilitation G. John Mullen, 
APPENDICES, 
Notes, 
Glossary, 
Notes on contributors, 
Index, 
Table of measurements, 
Acknowledgments, 

CHAPTER 1

hydrodynamics

Tiago M. Barbosa

Hydrodynamics play a significant role in the swimmer's performance. This chapter provides insight into how the water interacts with the swimmer and the forces acting upon the body. It examines the way water flows around the swimmer and how the forces produced can have an impact on the energy expended during swimming, and hence on the swimming efficiency. Swimmers, coaches, and researchers spend a good deal of time trying to understand how to optimize these key aspects. Cutting- edge devices are used to assess the swimmers, making them more efficient and improving their performance. These assessments can encompass the way the body is aligned, swimwear, or small details such as the position of the fingers during swimming.

What is the free body diagram of a swimmer?

-> What are the forces acting on me when I swim?

To have a deeper understanding of the swimmer's hydrodynamics we need to learn what the main forces acting upon the body are and how they interplay. Ultimately, swimming acceleration and speed depend on propulsive forces, resistive forces, and inertial parameters. Propulsive forces are those related to the thrust and forward movement. Resistive forces act opposite to the swimmer's direction of displacement. The inertial parameters are related to body features (anthropometric characteristics).

Thrust is due to steady and unsteady flow patterns (see here), and is the sum of propulsive drag, lift force, and the jet vortex (see here). The resistive force is also known as total drag force and results from three components — friction drag, pressure drag, and wave drag. Regarding the inertial parameters, these include the swimmer's body mass and the added mass of water.

Based on these external forces it is possible to model the swimming stroke and make a rough estimation of the acceleration-time and speed-time curves within the stroke cycle (see here). The swimmer does not move at a constant speed — that is, with uniform motion. Instead, over a stroke cycle, there are positive and negative accelerations. The typical profile of these curves depends on the swimming stroke, but in general positive accelerations occur when the thrust is greater than the drag force — for instance, during the pull phase. On the other hand, acceleration is negative when the thrust is smaller than the drag force — for example, during the arm's recovery. Therefore, one can swim faster by increasing the thrust while keeping the drag constant, by keeping the thrust constant and decreasing the drag, or by both increasing the thrust and simultaneously decreasing the drag force.

What is the influence of water flow on a swimmer's displacement?

-> How does water surround me as I swim?

Water, like any fluid, is a substance that flows and deforms when forces are applied to it. The way water flows around a swimmer affects several forces that act on the body, including the thrust (see here) and the resistance (see here). Fluids, such as water, are characterized by a set of properties. The most important are the density (mass or quantity of matter per unit of volume), and the viscosity (resistance to the movement of particles in the flowing substance).

The flow can be steady or unsteady. A flow is characterized as steady when there are no changes in the fluid velocity and pressure at a given point of the body over time. Conversely, if these properties change, the flow is unsteady. Both steady and unsteady flows play determinant roles in the production of thrust.

If the swimmer's limbs are moving at a constant or almost constant speed, with no significant changes in direction, then the water properties do not change over time and conditions are steady. Under these conditions, there are two propulsive forces, which are the drag and the lift produced by the hands and feet, whose speed and orientation are constant (see here).

On the other hand, when the swimmer's hands or feet accelerate or change direction suddenly, unsteady flows are created and this produces thrust. The speeds of the hands and the feet increase over their underwater trajectories. The hands accelerate from their entry into the water to their exit, and the feet also undergo accelerations as they kick up and down. In analyzing these unsteady conditions, we can assess the water circulation around the body or the limbs and observe, for instance, the generation of vortices.

Flow can also be described as laminar or turbulent. The flow is laminar when the layers of fluid are well organized and parallel to the swimmer's body. If the water layers show a random organization then this is turbulent flow.

How does drag force affect swimmers?

-> How does water resistance affect how I swim?

When an object moves through a real fluid such as water, which has viscosity and compressibility, there is always some resistance to overcome. This resistance is known as drag, because the object drags fluid particles along as it moves. Drag forces acting upon the body are a major concern because they slow us down, and can significantly affect performance.

The magnitude of the drag depends on a set of variables. The higher the fluid's density, the higher the drag, and this partly explains differences in salt water and fresh water performances. Water is about 800 times more dense than air, which means drag impacts a swimmer far more. Body surface also affects drag on a swimmer — the larger the area presented, the greater the drag. But the top determinant is the relative velocity between the body and the water — the faster you go, the more resistance there is to overcome. Drag forces can be broken down into three different components — skin friction drag (or viscous drag), pressure drag (or form drag), and wave-making drag.

Skin friction drag results from interaction between the water's viscosity and the body's surface. The water layer in contact with the skin sticks to it, and travels at the same speed as the body, so the relative speed is zero. This is the boundary layer. The next layer of water is decelerated by this layer, and so on, progressively further from the body. The higher the skin friction drag, the more water is dragged (or trailed) behind the body.

Pressure drag is related to the pressure difference between the leading and trailing edges of the body. At the front, there is high pressure where fluid particles are compressed. Particles then flow around the body, and eventually separate from the body at the boundary layer separation point. Beyond this, the flow reverses, producing vortices and a low-pressure region. The pressure differential means particles tend to move from the front to the rear of the body, "pushing" it backward — that is, producing pressure drag opposing the direction of movement.

Wave-making drag reflects the energy needed to push the water out of the way in swimming. As the body moves forward, fluid tends to "pile up" at the front, while "hollows" are produced in the rear, creating waves. Wave making decreases swimming efficiency in two ways — first, it takes energy that could have been used for forward movement, and second, waves reflected from the pool walls collide with the swimmer, transferring momentum and impeding performance.

equipment: computational fluid dynamics

Computational fluid dynamics (CFD) is a cutting-edge technique used to model a swimmer's hydrodynamics. It has origins in the aerospace industry, and was only applied in sports, notably in competitive swimming, during the late 1990s and early 2000s. Medicine, architecture, automobile design, and biology are other fields that frequently use computational fluid dynamics. CFD allows us to visualize how fluid (air or water) flows around a body, and to quantify key parameters such as drag and propulsive forces. The technique uses numerical analysis and a set of algorithms to solve problems related to water flow, which can help swimmers improve their performance by understanding the effects of changing body position, for example, or of using different garments (swimwear, goggles, caps). For instance, CFD can be used to model the effects of different finger positions on thrust, or of different swim suit designs on the drag force.

There are three main steps involved in performing an analysis using CFD. During pre-processing, relevant data is collected and prepared. Once these data are entered as a set of inputs, then the simulation is run. Because of the complexity of the calculations, the simulation is run on dedicated software. Finally, during post-processing, the output of the simulation is retrieved. For a given set of inputs, the output will be always the same. But if we slightly change one or several inputs, the output changes accordingly, modeling the effects of those inputs in a real-world system.

A major advantage of CFD is that it is possible to test a wide variety of inputs, until the best result is reached, with no need of physical experimentation or testing. So instead of inviting a swimmer to perform several trials in the pool under different conditions, we can simulate the effects in silico — that is, using software. Swimming performance depends on marginal changes in a given technique or characteristic. To investigate the effects of such small changes, CFD is more accurate than experimental testing, if properly conducted. The main drawback is that if the inputs are not specific and accurate enough the output will be less reliable. Hence, pre-processing is the step that takes most time — making sure the inputs are accurate increases the quality of the output. Another limitation of CFD is the cost involved, because of the huge computational resources needed to run the simulations.

Is drafting beneficial during training, open water and triathlon competitions?

-> Why is it easier if I swim behind another swimmer?

Anyone who has swum a few laps in a pool trailing behind a fellow swimmer will have felt that the effort is less than swimming alone. This happens quite often in training settings in competitive swimming, but also in open water and triathlon events. The lower effort perceived when swimming behind someone is due to drafting effects. The aim of the drafting technique is to diminish the drag force. This happens when two or more swimmers are in a close group and fairly well aligned.

Behind the leading swimmer, a region of slipstream is created, as the wake of water is displaced at a similar velocity to that of the swimmer. The slipstream region depends on the shape of the body — humans do not have a perfect hydrodynamic shape so the slipstream is rather big. The water flow over a swimmer's body is typically turbulent (see here), which means that the pressure in the slipstream region is lower than in the surrounding environment, creating a perceptible "suction effect."

Drafting involves a swimmer staying inside the slipstream region of a fellow swimmer in front. This is beneficial for both swimmers when moving at the same speed. Because the swimmer behind is inside a region of lower pressure in the slipstream (a "suction region"), he or she needs to expend much less energy and power to move forward. Wave drag may also be reduced in close-in drafting positions due to the decreased relative velocity of the disturbed flow close to the lead swimmer, which means smaller waves are created by the drafting swimmer.

Drafting is also a benefit for the leading swimmer. As we saw shown here, pressure drag is due to the pressure difference between the leading and trailing edges of the swimmer's body — a larger difference creates a greater pressure drag. When a swimmer is trailing behind the leading swimmer, the effect of the low-pressure region is reduced, and this therefore decreases the pressure drag on the leader.

What is a swimmer's hull speed?

-> What is the fastest I can swim?

Just like a boat, a swimmer moving over the surface pushes water out of the way. In doing so, the swimmer compresses the water particles and creates waves. Creating waves takes energy, which is not then available to propel the swimmer forward. So the swimmer is wasting energy that could instead be used for more efficient displacement.

A wave has a crest (the highest point or peak) and a trough (the lowest, deepest point). The amplitude is the height of the wave, from the midpoint to a crest, and the wavelength is the distance between two consecutive crests. As swimming speed increases, the wavelength of the created waves also increases. At a certain speed, the wavelength is equal to the swimmer's height or body length — this is known as the swimmer's "hull speed."

Taller swimmers have a higher hull speed. Younger swimmers, because they are still growing, will increase their hull speed over time. Some researchers consider that, theoretically, the hull speed is the maximum speed that a swimmer can reach. Others, though, have reported elite swimmers displacing at speeds higher than their hull speed. In such cases, the swimmer is effectively swimming uphill to ride the wave.

So what are the relative benefits of swimming between two crests at the hull speed, or of riding up the wave? It seems that a pace enabling the swimmer to be between two wave crests is more economical. The swimmer is not repeatedly hitting the wave, and so is able to maintain a smooth and even pace. Sprinters, however, are willing to expend more energy to ride the wave, using some of the wave's momentum to help them move forward. When this happens, wave drag drops significantly and the speed can increase substantially.

Over a full freestyle swim stroke, the hull speed probably shows some slight variations. During the arm's entry the "hull" of the swimmer is effectively longer because the arm is fully stretched in front. Moreover, as the arm enters the water it may smash the wave. However, once the arm is in the water, fully immersed and moving through its underwater path, the "hull" length corresponds to the swimmer's height once again, and the head and shoulder immediately create a new wave.

What are the thrust mechanisms in swimming?

-> How do I propel myself in the water?

A swimmer's displacement in the water depends on the relative magnitudes of the forward force, or thrust, and the drag force acting in the opposite direction (see here). In order to generate thrust, the swimmer must produce movement in several body segments, notably the arm stroke of the upper limbs, and the kicking action of the legs. In freestyle, about 10–15% of the total body speed is due to the kicking motion, and the remaining 85–90% is attributed to the arm stroke. For the other competitive swim strokes, the relative contributions of upper and lower body movements are not yet clear, because of lack of research evidence. However, based on educated guesses, practitioners argue that the percentages will be roughly the same for backstroke and butterfly, with the contribution of the kicking action being much higher for breaststroke.

Both upper (arm, forearm, and hand) and lower limbs produce thrust, by three main mechanisms — propulsive drag, lift force, and vortices. Propulsive drag is underpinned by Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. So when the water is pulled backward, as a reaction the body is propelled forward. That is why over the arm stroke the limbs rotate in the opposite direction to the body's motion — the arms move backward so that the body moves forward. The larger the propulsive surface, the more water is displaced and hence the higher the magnitude of this force. Another factor is the arm's speed — the faster the displacement the greater the force produced.

If the arms moved in a straight line trajectory underwater, the propulsive drag would be the only force acting. However, elite swimmers perform a curved arm stroke in order to produce a second force — the lift. Each arm acts as a hydrofoil, which — because of the angle of attack resulting from the curved stroke — is able to produce lift.

Vortices provide another source of thrust. A vortex is a rotating mass of fluid, shed backward when a limb suddenly changes direction, speed, or angle of attack, which results in a forward acceleration of the swimmer. This is why a swimmer should rapidly transition between up-down and down-up leg motion when kicking, for instance, and should accelerate the hand under the water from entry until exit.

(Continues...)

Excerpted from Swimming Science by G. John Mullen. Copyright © 2018 Quarto Publishing plc. Excerpted by permission of The University of Chicago Press.
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Edition details

• Publisher: University of Chicago Press
• Publication date: 2018
• Language: English
• ISBN 10: 022628784X
• ISBN 13: 9780226287843
• Binding: Hardcover
• Edition number: 1
• Number of pages: 192
• Editor: Mullen G. John