Equine Exercise Physiology E-Book

David Marlin

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 851

Veröffentlichungsjahr: 2013

Beschreibung

Equine exercise physiology is an area that has been subject to major scientific advances over the last 30 years, largely due to the increased availability of high-speed treadmills and techniques for recording physiological function during exercise. Despite the scientific advances, many riders and trainers are still using little more than experience and intuition to train their horses.

The aim of this book is to sort the fact from the fiction for the benefit of those involved in training, managing or working with horses, and to provide an up-to-date summary of the state of play in equine exercise physiology. Scientific theories are explained from first principles, with the assumption that the reader has no previous scientific background. The book is designed to save competitors and trainers a lot of time and effort trying to extract information in piecemeal fashion from a host of reference sources. For the first time, everything you need to know about exercising and training horses is here in one text.

Leseprobe

Contents

Foreword

Acknowledgements

Part I The Raw Materials

1 Introduction

Why train?

What are the aims of a training programme?

Exercise, work, training, fitness and performance

2 Energetics of exercise

Introduction

The resting horse

The energy for muscle contraction

The conversion of food into useful energy for exercise

Energy pathways

Energy partitioning

Size of the fuel stores

Running out of energy

3 Muscles

Introducing skeletal muscle

Inside the muscle cell

How does the nerve impulse make the muscle contract?

Properties of muscular activity

Muscle fibre types and distribution

Type I fibres (red endurance muscle)

Type II fibres (white sprint muscle)

Muscle capillary supply

Muscle fibre recruitment

Distribution of muscle fibre types

4 Connective tissue

Tendons and ligaments

Bones

5 The respiratory system

Respiration, breathing, ventilation

Anatomy of the respiratory system

How much air goes in and out?

What makes the air go in and out of the lung?

Pleural membranes

Ventilation–perfusion matching and mismatching

How easy is it to inflate the lungs?

Getting gases across the alveolar–capillary membrane

6 The cardiovascular system

Types of blood vessel

The heart as a pump

Cardiac output

Electrical conduction through the heart

The cardiac cycle

The electrocardiogram (ECG)

Control of blood flow

Control of blood pressure

The composition of blood

Red blood cells (erythrocytes)

Haematology and clinical biochemistry

Part II Exercise and Training Responses

7 Muscular responses

The muscular response to exercise

The muscular response to training

How long does it all take?

How long does it all last?

8 Skeletal responses

Mechanical properties of bone

The influence of exercise on modelling and remodelling

The responses of bone to training

Training bone in practical terms

Responses of cartilage to training

Responses of tendons to training

9 Respiratory responses

The oxygen pathway and

Ventilation

Respiratory–locomotory coupling

Alveolar ventilation ()

Is respiratory–locomotory coupling over-rated?

Pulmonary resistance

The struggle to breathe

The work of breathing

Exercise-induced arterial hypoxaemia

Respiratory response to training

10 Cardiovascular responses

The heart in exercise and performance

Maximal oxygen uptake ()

Splenic reserves

Blood pressure during exercise

Matching oxygen demand and supply

The cardiovascular response to training

11 Aspects of physiological stress and fatigue

Stress

12 Thermoregulation

Replacing fluid losses

Replacing electrolyte losses

Assessing environmental thermal stress

Acclimatisation and acclimation

Management of competitions in thermally stressful environments

Thermoregulation in the cold

13 Introduction to biomechanics

Studying the gaits

Kinetics and force plates

Studying kinematics

Stride length and stride frequency

The gaits

Gallop

Gait transitions

The rider

Energy cost

The jump stride

Spinal kinematics and back problems

Bow and string theory

Part III Applications of Exercise Physiology

14 The demands of equestrian sport

Eventing

Endurance

Racing

Showjumping

Polo

15 Training principles

Horses are natural athletes

Training objectives

Training specificity

Identify the challenge

Training intensity, frequency, duration and volume

Tapering for peak performance

Overtraining

Detraining

16 Training facilities

Training and racing surfaces

Hoof–surface interaction

Treadmills

Swimming pools

Water treadmills

17 Practical training

How fit does the horse need to be?

How long will it take?

Can you bring all the systems to a peak at once?

How do I construct a training programme?

How should interval training be carried out?

Learning to ride at a set speed

How hard should the horse work and how soon should I increase the intensity?

Load carried

Ideal body condition

How long can you keep a horse at a peak?

What do you do if the horse has an enforced lay-off?

Keeping athletes on the road

18 Exercise testing

Why would you want to use an exercise test?

Standardisation and specificity

Examples of field exercise tests

Fitting a heart rate monitor

Simple field tests using a heart rate monitor

Treadmill testing

Comparison of overland versus treadmill exercise

Types of treadmill test

What can you measure on a horse exercising on a treadmill?

19 Indicators of performance

What is performance testing?

Which is best – field tests or treadmill tests?

The effect of training on indicators of performance

Biomechanical indicators of performance

Poor performance and loss of performance investigation

20 Feeding performance horses

What do we want from a feed ration?

Water – the most important ingredient

Water and electrolytes

Meeting total daily energy requirements

Quick release and slow release of energy

Monitoring body mass and condition

Minerals for performance horses

Herbal supplements

Miscellaneous supplements

Drugs and performance

21 Transport

What happens to a horse during transport?

Weight loss during transport

Recovery following transport

Recommendations for preparation, transport and acclimatisation for the 1996 Atlanta Olympic Games

References

Further Reading

Index

© 2002 by Blackwell Science Ltd,

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All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher.

First published 2002

Reprinted 2003

Library of Congress

Cataloging-in-Publication Data

Marlin, David.

Equine exercise philisophy/David Marlin, Kathryn

Nankervis.

p. cm.

ISBN 0-632-05552-9

1. Horses–Training. 2. Horses–Exercise. I. Nankervis,

K.J. II. Title.

SF287 .M34 2003

636.1′0835–dc21

2002026041

ISBN 0-632-05552-9

A catalogue record for this title is available from the British Library

For further information on

Blackwell Publishing, visit our website:

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Foreword

The training of competition horses has changed a great deal over the last few decades, for example with the introduction of the all weather gallop and the ‘interval’ method of training for staying horses.

This book explains the scientific reasoning behind the training of horses for competition in a manner that those working with horses will comprehend. It explains why training methods succeed and, just as importantly, if your horse is over stressed why those methods might fail.

The trainer of today’s horse is presented with a different set of problems from those of yesteryear. Arguably the competition is now tougher, which puts a horse under greater stress, and trainers are presented with ever more information about the condition of their horses – blood tests, food analysis and so on. We need to have at the very least a basic understanding of these factors if we are to make rational decisions about what is best for our horses. This book will help you understand how to manage your competition horse in today’s environment.

Equine Exercise Physiology is a readable, up-to-date account of how to achieve the highest standards in your competition horses. It will suit all horse enthusiasts and students, as well as experienced trainers.

Peter Scudamore

Acknowledgements

The authors would like to thank the following friends and colleagues for comments on various chapters within this book: Rachel Neville (Chapters 2 and 20), Dr Stephanie Valberg (Chapters 3 and 7), Dr Rachel Murray (Chapters 4 and 8), Dr Bob Colborne (Chapters 4, 8 and 13), Dr Colin Roberts (Chapters 5, 9 and 18), Dr Lesley Young (Chapters 6 and 10), John Robertson and Rod Fisher (Chapter 14), Dr Catherine Dunnett (Chapter 20), Matthew French at Hartpury College for assistance in the production of the figures and Dr David Evans, Equine Performance Laboratory, University of Sydney, for providing Fig. 18.10.

Cover photo: Courtesy of Dr D.J. Marlin.

To Roma and George (DM)

To Tom (KN)

Part I

The Raw Materials

Chapter 1

Introduction

Why train?

In theory and in practice, the horse must surely be considered the best all round athlete of the animal kingdom. Horses are not great thinkers or fighters, they are runners. Whatever the breed or type of horse, they are all blessed with the same basic structure and the same basic physiological mechanisms; therefore they all have the potential to respond favourably to training. A horse’s performance, i.e. how fast it runs, how high it jumps, is largely determined by its natural ability, and to a lesser extent by its level of training. Natural ability is determined mainly by the genes the horse inherits from its parents (Fig. 1.1). We can’t do anything about the genes an individual horse has once it has been born, but we can do something about the training. To reach a horse’s genetic potential for performance, whether it is aimed at local riding club events or the Derby, it must be fit! From the unfit to fit state the horse undergoes a metamorphosis and its shape, its gaits, its looks, often even its attitude to life, are altered. Whatever we strive to achieve with our horses, there is much to be gained by making sure that they are fit enough for the task. To compete on an unfit horse puts both you and your horse at risk, quite apart from decreasing your chances of success and also the likelihood of the two of you going on to compete year after year.

Horses are always huge investments in terms of both time and money. If you aim to compete at any level, it pays to improve the horse’s chances of completing the work goals without risking mechanical breakdown and so incurring large veterinary bills, long periods of rehabilitation at best and destruction at worst. There is no doubt that training is an art, but a little understanding of the physiology of the horse can help anyone perfect their own art. Much of what we currently understand about equine exercise physiology has been established in the last 20 to 30 years, largely as a result of an increased scientific and veterinary interest in exercise physiology, improvements in technology, and availability of equipment such as high speed treadmills. High speed treadmills enable vets and scientists to study the horse in controlled situations where the speed, distance, slope, going and environmental conditions can all be closely regulated. In addition, with a horse exercising on a treadmill it is a very simple matter to collect a blood sample from a catheter in an artery or vein, or to measure how much oxygen the horse is using. Procedures such as these are either difficult or at present not possible to undertake in the field. Inevitably, running on treadmills is not the same as running round a racetrack or a cross-country course, but it has enabled scientists to make great advances in the study of the horse’s responses to exercise and training. Many of these advances can now easily be applied to the management and training programmes of our own competition horses with a good degree of success. Whilst science cannot guarantee a winner, it may well shorten the odds in our favour.

What are the aims of a training programme?

What exactly are we trying to achieve as a result of training? The fundamental purposes of any training programme are to:

(1) Increase the horse’s exercise capacity

(2) Increase the time to the onset of fatigue

(3) Improve overall performance, by increasing:

— Skill

— Strength

— Speed

— Endurance

or all four of these

(4) Decrease the risk of injury.

Fig. 1.1 A horse’s performance is largely determined by the genes the horse inherits from its parents.

By analysing the adaptations the horse makes in the short term (during exercise) and in the long term (throughout training) we can begin to understand how to design the horse’s work programme to achieve these aims (Fig. 1.2).

Exercise, work, training, fitness and performance

First of all, let’s tackle the vocabulary of ‘exercise physiology’. Being associated with horses entitles you to become a member of a club that has its own language, a language which is only understood by those ‘in the know’. Consider some of our expressions: we talk about grey when we mean white; we ‘break’ horses when we are introducing them to being ridden; a three-day event can be held over 4 days. What chance do outsiders have? Scientists also have their own language, one that is universal amongst all sorts of them, such as biochemists, geneticists, physiologists, etc. To be able to translate the results of scientific studies and apply them to real-life training situations we need to become familiar with the scientific vocabulary associated with equine exercise physiology.

Fig. 1.2 Requirements for speed, strength and endurance in a range of equestrian sports.

Physiology is the study of the function of cells, tissues, organs and whole systems. Exercise physiology is thus the study of all systems involved in exercise. Exercise is a good example of a word commonly used in completely different contexts by scientists and horse people. Horse people often differentiate between lungeing a horse either for exercise or for work. The horse person’s interpretation of this is that by lungeing for exercise you are merely allowing the horse to ‘stretch its legs’ on the end of the lunge line, but it is not asked to do anything too taxing. Lungeing a horse for work means that it would probably wear side reins or maybe a ‘gadget’, e.g. a pessoa, and would be asked to engage its hindquarters and carry itself in a correct outline. To a scientist, work refers to the energy used up when an object moves a known or fixed distance; the amount of work done is described in terms of the energy used and is commonly measured in units such as joules (J) or kilojoules (kJ), or calories (cal) or kilocalories (kcal). A force has to be applied in order to perform work, and this force requires energy to be expended. Therefore the horse is doing work simply by moving from A to B. In scientific circles, ‘work’ does not infer anything about the quality of the movement (i.e. speed, distance or direction), simply that something has moved. In fact, in strict scientific terms, it takes the same amount of energy to move a horse from A to B at a walk as it does at the gallop: the difference is in the rate at which energy is used. The same amount of energy is required to move from A to B, regardless of the speed, but when the horse moves at the gallop, the rate of energy utilisation must be greater. The rate of energy usage is referred to in terms of power. Power is measured in terms of the rate of work done (units of energy per unit time), e.g. in joules per second or watts. In galloping from A to B, the horse must generate more power than if he walks from A to B. Exercise refers to any movement or activity, so as soon as the horse moves off from a standstill, it is performing exercise. To use our scientific terms, if the horse is exercising, work is being done.

Training is another term that may have different interpretations depending upon the context in which it is used. To horse people, ‘training’ often implies that the horse is learning: its ‘basic training’ is its basic education. To an exercise physiologist, training is a long-term process of repeated bouts of exercise, which results in an improvement in fitness, where fitness refers to a certain capacity for exercise. Training for improvement in fitness is sometimes also referred to as ‘conditioning’, particularly in the USA.

Throughout exercise and training, the horse’s body should make certain physiological adjustments, adaptations or responses. An exercise response is any short-term physiological adaptation that is made as a result of an increase in the level of muscular activity, whilst a training response is a long-term physiological adaptation to repeated bouts of increased muscular activity. Exercise responses tend to return to baseline levels after the work is done. For example, during exercise there is an increase in heart rate, corresponding to the intensity of the work done. When the horse stops exercising, the heart rate will gradually return to resting levels. Training responses are more long lasting and are maintained as long as the horse continues to regularly undertake a certain volume of work. For example, a training response may be an increase in heart mass (weight) or an increase in the number of capillaries (small blood vessels) around each muscle fibre. Changes such as these occur over a period of time as the horse responds to a gradual increase in workload, but they do not change throughout the course of an exercise bout. Training changes are mainly mediated through activation of genes that may then ‘code’ for greater production of an enzyme in an aerobic energy pathway, for example.

Fig. 1.3 Training leads to an increase in fitness and an improvement in performance.

The type of work undertaken is particularly important in determining whether or not a training response is induced. For example, walking a horse 16 km (10 miles) a day, 3 days a week for a month may produce a noticeable loss of body mass (bodyweight) as the horse will be using up a considerable amount of energy on each of these walks. However, it may do very little in terms of increasing fitness, i.e. producing a training response. When we think about training it is therefore not simply how much energy we use, i.e. the volume of work, that counts but the way in which that work is done, i.e. the quality of work, to induce appropriate training responses.

In summary, if we want to improve our horse’s performance, we would do well to increase their fitness (Fig. 1.3). This can be done by carrying out regular exercise, of progressively increasing workloads, to bring about the necessary training responses. The key is knowing what is the right work for what sport and when to settle for less than 100% fitness to reduce the risk of injury that might come from training very hard for a long time.

KEY POINTS

Horses are natural athletes.Probably the biggest impact we can have on how well a horse performs is through training.The aims of training are to increase the time to the onset of fatigue, improve performance and decrease the risk of injury.Physiology is the study of the function of cells, tissues, organs or whole systems.Exercise means that work is done and so by definition energy is used.Exercise responses, e.g. an increase in heart rate, are short term.Training is a longer process of many repeated bouts of exercise that brings about an increase in fitness.Training responses, e.g. an increase in heart size, occur over a relatively long period of time.

Chapter 2

Energetics of exercise

Introduction

A little knowledge of biochemistry is a powerful thing! When you first become aware of the cellular processes involved in the conversion of nutrients into mechanical energy for muscle contraction it is like an enormous penny dropping, making so much of what the nutritionists tell us fall into place. For performance horses, one of the most important considerations is the energy content of the diet. To make sure our horse has enough energy for exercise, it helps to understand something about the way the horse’s muscles obtain energy from nutrients within the diet, and this forms the basis of the study of the energetics of exercise. Awareness of the energetics of exercise can help us formulate a diet to achieve a specific result. As far as interpretation of energetics is concerned, the horse is not dissimilar to a car: we input fuel at great expense and we expect a certain performance in terms of mechanical output. The horse, like the petrol engine in a car, is required to perform mechanical work. Unlike cars, however, the horse can run on a variety of fuels, and we can expect to see a difference in performance depending upon the type of fuel we put in.

Horse diets usually vary from being 100% forage-based to about 80% cereal-based. We should never feed a 100% cereal-based diet to horses, because they need a certain minimum amount of forage for effective functioning of the digestive tract. Consequently, most horses are fed a combination of forage and cereals which has to be broken down by a combination of mechanical, chemical and microbial digestive processes. The products of digestion are then absorbed into the bloodstream mainly from the small and large intestine. Some of these products may be used immediately to supply energy for muscular contraction, but the majority are more likely to be converted to fuel stores within the liver, muscle and adipose tissue (fat) to be used at a later date. Regardless of the type of feed we put into the horse, all the nutrients capable of releasing energy for work (glucose, fatty acids and amino acids) are ultimately converted to just one vital ingredient – ATP or adenosine triphosphate. ATP is our energy ‘currency’ that is required for normal functioning of all cells both at rest and during exercise.

The resting horse

A certain amount of fuel must be provided within the diet to support the horse’s energy requirements at rest and to do so whilst maintaining its body mass. Within 1 or 2 hours of a meal, particularly a cereal meal, the levels of glucose in the horse’s blood rise from about 5 millimoles per litre (mmol/l) of blood to about 7 mmol/l of blood. In response to this increase, the pancreas increases the secretion of insulin, a hormone that acts to decrease blood glucose, and several hours later the blood glucose levels are restored to 5 mmol/l. Insulin brings about a lowering of blood glucose by increasing the uptake of glucose into the muscle and liver. In other words, in times of plenty the emphasis is on accumulation of potential fuel sources within the liver and muscle. This ensures that muscle has sufficient fuel stores should there be an increase in muscle activity, and also that the liver has sufficient fuel stores to ‘buffer’ fluctuations in blood glucose arising as a result of exercise. Whilst glucose has a very important role in providing energy for muscular contraction, it is far more important from a physiological ‘housekeeping’ perspective to ensure that the brain and the heart are provided with glucose, because glucose is the primary fuel source for these vital organs. One of the most important functions of the liver, aided by a number of hormones, is to act as a ‘glucostat’, i.e. a regulator of blood glucose, ensuring that blood glucose does not significantly decrease or increase, thereby guaranteeing a constant supply of glucose for the brain and heart, regardless of whether the horse is fed, starved, exercised or rested.

The energy for muscle contraction

Energy cannot be created or destroyed: it is merely converted from one form into another. All animals convert chemical energy from food into mechanical energy of work and heat is given off as a byproduct. No process of converting stored or potential energy into work or movement is 100% efficient. In fact, animals (including humans) are rather inefficient energy converters, with only around 20% of the energy obtainable from food being converted into useful work, i.e. used for movement by muscle, and the rest (about 80%) being released as heat. To put this in context of mechanical engines, modern car engines would be able to convert around 20–30% of the potential energy in petrol into movement.