Swimming Science: Optimizing Training and Performance

Discover the secrets of physiology, hydrodynamics, and other scientific aspects of swimming to enhance your skills and speed!

Low-impact, beneficial at any age, and just plain fun, swimming is an excellent workout—and the same scientific principles apply whether you’re competing for a medal or practicing your backstroke in the backyard. 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?

In this enlightening and useful volume, contributors 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 and more are examined with the aid of explanatory diagrams and illustrations. No matter whether you swim for exercise, enjoyment, or athletic achievement, Swimming Science adds a new dimension to the sport.

“Swimming Science is a wonderful read for those interested in understanding how extraordinary athletes have been able to swim at incredible speed. But it is also an inspiring and potentially transforming read for ordinary people for whom swimming is simply a love story with the water.” —American Journal of Public Health

• Language: English
• Publisher: Open Road Integrated Media
• Release date: Jul 27, 2018
• ISBN: 9780226287980

Book preview

Swimming Science - Optimizing training and performance

swimming science

optimizing training and performance

Edited by G. John Mullen

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

Introduction

Swimming is a popular sport for people of all ages. Children are often first exposed when they learn to swim for safety, perhaps starting with splashing and then doing turns and tumbles, enjoying the feeling of weightlessness and the novelty of being in water. In fact, swimming is a truly unnatural activity for humans, requiring swimmers to be instructed from their first stroke.

Unlike any other sport, swimming requires athletes to move as rapidly as possible through a medium more dense than air. The density of water makes the precision of every action important, as the additional resistance of an improper action greatly reduces swimming velocity. Understanding the science behind swimming therefore enhances both proficiency and enjoyment in the sport.

Since appearing in the 1896 Olympics, competitive swimming has seen vast changes in style, form, attire, and location. At first, swimming events were held in open water, before switching to the pool in 1908. Male competitors wore full-body swim suits up until the 1940s, and the nature of fabrics available at the time meant this significantly increased the drag on the swimmer. Lane markers were not used before 1924 and starts weren’t incorporated until 1936. Swimming goggles were not allowed until as late as 1976.

From across the globe, Swimming Science brings you the insights of leading experts in physical, mental, technical, and tactical aspects of the sport. This book binds together their significant findings with those of scientists who have parsed and studied every element of swimming, most notably the original swimming scientist, Doc Counsilman. Some discoveries were made in the nineteenth century and others as recently as this year. A wide range of sciences is embraced here, as swimming involves a surprisingly diverse array of disciplines. For example, at different stages of his career, Michael Phelps—arguably the greatest male swimmer of all time—has relied on various aspects of science to hone his swimming to ever more impressive levels. His technical skills, strong work ethic, and training base were developed as a young swimmer in Baltimore, Maryland. He has subsequently concentrated on physical preparation—a key factor in his relatively injury-free career—and has cultivated a mental toughness that has been severely tested under daunting pressure to win multiple gold medals, resulting in amazing race finishes with Milorad Cavic.

With the help of advanced swimming science Michael Phelps became the most decorated Olympian of all-time.

Each chapter in this book deals with a different scientific discipline, providing the reader with the background to better understand the sport. A single solution doesn’t work for every swimmer, so instead of offering a panacea or list of drills, the authors present science-based approaches that enable one to tailor solutions to individual situations. Chapter 1, Hydrodynamics, breaks down how the water interacts with the body during swimming. Understanding how to stay streamlined in the water and how various joint positions create torque and power is essential in the sport. The biomechanics of effective swimming strokes are dealt with in Chapter 2, Technique. Unlike in other sports, technique is the greatest contributor to success in swimming, yet remains the area requiring most improvement, for the majority of swimmers. Some aspects of technique are not included due to space limitations, such as kicking, breaststroke timing, freestyle and butterfly arm recovery, backstroke finishes, relay take-offs, and turns. Chapter 3, Training, discusses the physiological demands of swimming and how training influences swimmers’ ability to deal with these. Competitive swimming today requires a very high level of physical performance, so Chapter 4, Dryland Training, delves into the science behind improving fitness and strength through training outside of the pool. Chapter 5, Nutrition, considers the optimal proportions of different foods and fluids for swimmers to consume, to regenerate the body for maximum performance. The sport’s heavy physical demands can lead to injury, so Chapter 6, Injury Prevention and Rehabilitation, addresses the best ways of preventing or minimizing the risks of tissue damage. Finally, each chapter includes a detailed look at how specialized equipment—such as that used in computer fluid dynamics, kinematics, and electromyography—has impacted swimming science, and the photographic Science in Action pages show how the professional sport has benefited directly from the application of scientific principles.

Whether you dip into the book for answers to specific questions or read it straight through for an overview, Swimming Science reveals the science at work when swimmer meets water.

Graphically speaking This book will introduce you to the science that has developed over many years of swimming practice, from the fundamentals of hydrodynamics and body biomechanics to the latest developments in swimming technology.

chapter one

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.

Free body This free body diagram shows the applied forces acting on a swimmer’s body while moving through the water at a steady speed. The lengths of the arrows are proportional to their magnitudes. Here, the forward thrust Fthrust and backward drag Fdrag are equal in magnitude, so there is no net force acting to accelerate the swimmer. The upward force Fup is a combination of buoyancy and lift resulting from the swimmer’s motion through the water. It is equal and opposite to the downward force Fmass, which is the swimmer’s weight.

Forces and inertia

Thrust

F thrust

Thrust (positive force, acting in forward direction) is the sum of several forces produced by the swimmer, based on steady or unsteady flows. These are propulsive drag (caused by pulling the hand directly backward), lift forces (caused by sculling actions of the hands) and the jet vortex effect, besides others. Thrust is produced by both upper and lower limbs.

Even though the surfaces of the feet and hands are the most important, there is evidence that the forearm, upper arm, shank, and thigh may also contribute to the production of propulsive drag, at least in some phases of the stroke cycle.1,2

Drag force

F drag

Drag force (negative force, acting backward) results from the collision between the swimmer and the water molecules, and is one of the main concerns for support staff (sport analysts), coaches and swimmers. The total drag force can be broken down into three main components—friction drag (or viscous drag), pressure drag (also known as form or profile drag), and wave drag. A great deal of effort has been made over the decades to understand the role of drag in swimming and how to minimize its effects. This can be achieved by improving swimming technique, designing new swimming apparel (such as swim suits, caps, goggles) and building pools with different specifications of depth and width.

Inertial parameters

The two main inertial parameters are the body’s mass and the added mass of water.

A body’s inertial mass is a measure of its resistance to changes in velocity—that is, to being accelerated. There is an inverse relationship between acceleration and mass according to Newton’s second law, F = m × a. Hence, the larger the mass m of the swimmer, the smaller the acceleration a for the same mechanical force F. The mechanical force F is the sum of the thrust Fthrust and drag Fdrag.

Total inertial mass is the sum of the swimmer’s mass plus the added water mass. When a body moves in water, it effectively drags some surrounding water with it. As a percentage of body mass, the added mass is roughly 24% for women and 27% for men.3 Newton’s second law equation becomes F = (m + madded) × a. The heavier the subject, the more added mass will be carried, compounding the inverse effect on acceleration.

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.1

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.

Laminar and turbulent flow

Let it flow When the layers of fluid are parallel and well organized with no disturbance, the flow is said to be laminar. The velocity and pressure at each point are constant, and the water around the body appears smooth. Laminar flow happens typically at slow swim speeds—for instance, when gliding in the streamlined position at a relatively low speed (A). At higher speeds, the water surrounding the body appears increasingly erratic, and swirling masses called eddies are observed, notably on the body edges. The water layers are no longer parallel—the flow is becoming turbulent (B). The resistance drag in turbulent flow is significantly higher than in laminar flow, so swimmers try to minimize turbulent flow as much as possible.

Flow analysis

Steady as you go We can visualize steady and unsteady flows using threads, or tufts, attached to the body (right).2 The swimming stroke is recorded on video and the tufts’ orientation inspected frame-by-frame. In this way, changes in a limb’s velocity and direction can be observed over the course of the stroke. Extreme changes in the tufts’ orientation from one frame to the next suggest that the flow direction changed suddenly. The arrows in the diagrams represent the speed and direction of movement of the hand, elbow and shoulder. Air bubbles or dye can also be injected into the water, and used for qualitative analysis of flow (below).3 Here, a swimmer is performing dolphin kicks. Each time the feet change from upward to downward movement, or downward to upward, there is a cluster of air bubbles. This allows us to observe the water circulation and vortices due to the sudden change of direction of the accelerated limb.

Reynolds number

To assess how laminar or turbulent the flow is, we can calculate the Reynolds number. This is a number that takes into account the water density, velocity, body length, and viscosity:

A young swimmer around 12 years old has a Reynolds number of about 2,500,000 at top speed.4 For the men’s 50 m freestyle world record holder, who is taller and faster, the Reynolds number is much higher, at around 5,200,000.

There is a critical Reynolds number value at which flow becomes turbulent. This depends on body shape but, as rule of thumb, flow becomes turbulent at about 500,000. In swimming, the transition from laminar to turbulent flow occurs somewhere between 500,000 and 10 million, so the flow surrounding a racing swimmer cannot be considered to be laminar.5

Variations across species

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.1

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.

Drag forces acting on a swimmer

Total drag The total drag on a swimmer D is the sum of the three components skin friction drag Df, pressure drag Dp, and wave-making drag Dw. That is, D = Df + Dp + Dw. Skin friction drag is directly proportional to swim velocity v, so it increases as the swimmer gets faster in a 1:1 relation. However, pressure drag is proportional to v², and wave-making drag is proportional to v³, so these components increase very steeply indeed with swim velocity.2,3 Pressure drag and wave-making drag in particular are extremely sensitive to changes in body position, and so—because these factors increase so drastically at greater speeds—the faster the swimmer goes, the more critical good technique becomes.

Separation point

Pressure effects If there were no boundary layer separation point, the pressures at the