Paediatric Exercise Physiology: Advances in Sport and Exercise Science Series

378 Pages·2007·3.51 MB·English

by  Neil Armstrong PhD DSc

This book is dedicated to Professor Oded Bar-Or, who died on 8 December 2005.
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First published 2007
ISBN-10 0 443 10260 0
ISBN-13 978 0 443 10260 8
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vii
Contributors
Neil Armstrong PhD DSc
Professor of Paediatric Physiology, Director of the Children’s Health and Exercise
Research Centre, University of Exeter, Exeter, UK
Adam D. G. Baxter-Jones PhD
Professor, College of Kinesiology, University of Saskatchewan, Saskatoon,
Saskatchewan, Canada
Michael Chia PhD
Associate Professor, Head of Physical Education and Sports Science, National
Institute of Education, Nanyang Technological University, Singapore
Mark B. A. De Ste CroixPhD
Principal Lecturer, Faculty of Sport, Health and Social Care, University of
Gloucestershire, Gloucester, UK
Roger G. Eston DPE
Professor of Human Physiology, Children’s Health and Exercise Research Centre,
University of Exeter, Exeter, UK
Samantha G. Fawkner PhD
Lecturer, School of Life Sciences, Heriot-Watt University, Edinburgh, UK
Clark A. Mundt MSc
Research Scholar, College of Kinesiology, University of Saskatchewan, Saskatoon,
Saskatchewan, Canada
Gaynor Parfitt PhD
Senior Lecturer, Children’s Health and Exercise Research Centre, University of
Exeter, Exeter, UK
Lauren B. Sherar MSc
Research Scholar, College of Kinesiology, University of Saskatchewan, Saskatoon,
Saskatchewan, Canada
Keith Tolfrey PhD
Reader in Paediatric Exercise Physiology, Department of Exercise and Sport
Science, Manchester Metropolitan University, Alsager, UK
viii CONTRIBUTORS
Jos W. R. Twisk PhD
Senior Researcher, Department of Clinical Epidemiology and Biostatistics,
University Medical Centre and Institute of Health Sciences, Vrije University,
Amsterdam, The Netherlands
Joanne R. Welsman PhD
Senior Research Fellow, Deputy Director of the Children’s Health and Exercise
Research Centre, University of Exeter, Exeter, UK
Craig A. Williams PhD
Senior Lecturer, Associate Director of the Children’s Health and Exercise Research
Centre, University of Exeter, UK
Richard J. Winsley PhD
Lecturer, Associate Director of the Children’s Health and Exercise Research Centre,
University of Exeter, Exeter, UK
ix
Foreword
It is now well accepted that, physiologically, children are not simply small adults.
Nevertheless, the ways in which they seem to differ from adults do not always meet
agreement. Take, for example, the question ‘Do children perceive a given level of
exertion as harder or easier than adults?’ – as evidenced, for example, by the Borg
RPE scale. This has been susceptible to a variety of differing interpretations. I would
suggest from my own (relatively limited) experience that young children perceive
treadmill running as correspondingly easier than adults – but others would indeed
disagree.
On the anaerobic fatigue side, often, working with England U-8, U-10 and U-12
boys squash squads, I would notice that if one set them the task of presumed anaer-
obic ‘shadow-training’ on the court – i.e. periods of 30 s of high intensity corner-to-
corner running, alternating with 30 s periods of active rest – these age groups would
(if one let them) complete sets of 15 or even 20 repetitions. Whereas the older squads
– U-14, U-16 and U-19 – would simply slow from fatigue at around 10 repetitions. Is
this due to a different maturational lactate response?
Knowing that the surface area of an 8-year-old may be some 40% greater, relatively,
than that of an adult can help explain why such children may be at higher risk of
appropriate thermoregulatory upset in cold water or hot sunshine; and may also help
in understanding how children can survive total ice-cold water immersion for periods
of over half an hour, their rate of cooling being so rapid that the cryogenic effect is
actually life-saving.
Nevertheless, knowing something is not always the same as acting on it. From an
early age I coached my son Duncan at squash. Once when he was about 8 years old, I
was feeding a long succession of balls for him to learn the overhead backhand volley.
Gradually he learned the skill, and was striking the ball well, when he lowered his
racket and said: ‘Do you mind if we stop, I’m getting too hot!’ Then I looked at my
red-faced wee son and realized that, although I of all people should have known of
the much poorer sweat and general thermoregulatory response of his age group, I had
completely overlooked it in my pleasure at his grasping the technique.
Oded Bar-Or’s 1983 text Pediatric Sports Medicine for the Practitioner was an
absolutely seminal publication for those of us even peripherally in the field of children
and exercise, containing as it did such a wealth of paediatric physiology. Afew years
ago, Professor Bar-Or was spending a sabbatical period with Professor Armstrong in
Exeter, and I was visiting. Somehow the question of which was the leading paediatric
exercise laboratory came up. ‘Well, yours is’, I said to Bar-Or. ‘No’, he said, turning to
Neil, ‘Yours is now.’ No higher compliment could have been paid, and it is noteworthy
that in the current volume, 11 of the 14 chapters are by staff or graduates of the Exeter
x FOREWORD
Children’s Health and Exercise Research Centre, displaying a comprehensive range of
materials from both their own research and the literature, relating to the physical
performance of children and adolescents.
The list of 14 topics is exactly what one would want, ranging from growth, scaling
and metabolism, through strength and high intensity exercise to pulmonary and
cardiac function, oxygen kinetics and aerobic fitness. The environment, perceived
exertion, responses to training, and the young athlete lead on to the final, vital chapter
on physical activity and health. Aknowledge of children’s physiology is relevant to
many aspects of work with young people, including medicine, sports science, sport,
teaching, physical education – and general parenting; and the range and quality of the
exercise science contained in the text form a database from which genuine advice of all
types and at all levels can be sought and provided.
Given that children are the veritable stem cells of society, the thrust of a book
leaning through their physiology into sport, activity and health cannot be over-
estimated in importance, especially at a time when there are worryingly adverse
trends in children’s fitness, fatness and disease. Abundant paediatric medical and
physiological data are scattered through the scientific literature, but naturally with a
marked lack of integration. Here the data are not only well presented and reviewed,
but synthesized into a coherent overall story in the book as a whole.
The publication of Paediatric Exercise Physiologywill provide a great deal of critically
evaluated information and approachable interest to a broad spectrum of readers.
Editor Neil Armstrong and his 13 contributors are to be very warmly congratulated on
a worthy successor to Oded Bar-Or’s superb text.
N. C. Craig Sharp
xi
Preface
This book will be of interest to scientists, physicians, paramedics, lecturers, teachers,
and coaches working with children and adolescents, but it is primarily addressed
to final year undergraduate and postgraduate sport and exercise science students.
An understanding of the basic principles of exercise physiology is assumed and the
primary objective of the book is to provide a state-of-the-art overview of the rapidly
emerging field of paediatric exercise physiology.
Chapter topics have been chosen to provide comprehensive coverage of the content
of taught modules in paediatric exercise physiology within a sport and exercise science
programme. Each chapter begins with a list of learning objectives and concludes with
a summary and a review of key points. Chapters are self-contained with selected
references for readers interested in particular topics but also cross-referenced to other
chapters where specific issues are examined in detail. A list of further reading is
provided at the end of each chapter for those who wish to pursue the topic in more
depth. The writers are all experienced lecturers and researchers in paediatric exercise
physiology and 11 of the 14 chapters are authored by staff or graduates of the
Children’s Health and Exercise Research Centre at the University of Exeter.
The dramatic increase in published research over the last decade has enhanced
understanding of the physiology of the exercising child, but in relation to research
with adults data are sparse. Children and adolescents are not mini-adults and research
techniques and equipment developed for use with adults are often not appropriate for
young people. The involvement of children in non-therapeutic research raises ethical
issues which have been debated at length elsewhere (e.g. Nicholson R H 1986 Medical
Research with Children, Oxford University Press), and, although reference to ethical
research is made where relevant throughout the text, detailed discussion is beyond
the scope of this book. However, researchers must consider carefully whether the
procedures they employ are ethical for use with young participants. Several
techniques used almost routinely with adults (e.g. muscle biopsies) are not normally
acceptable for research with healthy children, and paediatric physiologists must seek
innovative experimental solutions to research questions.
Research with children presents many challenges and much remains to be learnt
about physiological responses to exercise in relation to age, growth, maturation and
sex. If this book stimulates interest in the physiology of the exercising child and
encourages sport and exercise scientists to engage in research programmes devoted to
enhancing understanding of paediatric exercise physiology, it will have served its
purpose.
Exeter 2006 Neil Armstrong
1
1
Chapter
Growth and maturation
Adam D. G. Baxter-Jones and Lauren B. Sherar
CHAPTER CONTENTS
Learning objectives 1 Secondary sex characteristics 16
Introduction 2 Hormonal indicators of maturity 19
Study design 3 Relationship between indicators 19
Growth 3 Regulation of growth and maturation 19
Body dimensions and proportions 3 Maturity-associated variation in body size
Stature 5 and function 21
Body mass 7 The importance of controlling for
Body proportions 9 biological maturity 22
Controlling for biological maturity 9 Summary 22
Skeletal age 10 Key points 24
Age at peak height velocity 11 References 25
Menarcheal status 15 Further reading 26
LEARNING OBJECTIVES
After studying this chapter you should be able to:
1. define childhood growth, maturation and development
2. understand the difference between cross-sectional, longitudinal and mixed
longitudinal research design
3. interpret distance and velocity curves for height and body mass
4. describe growth changes in height, body mass and body proportions
5. understand why controlling for biological maturation is important in paediatric
studies
6. determine age at peak height velocity from a longitudinal data set
7. describe the advantages and disadvantages of different maturity indicators in
controlling for biological maturation
8. list some of the key regulators of growth and maturation
9. describe some differences in growth and performance among maturity groups
(i.e. early, average and late maturers)
10. describe gender differences in growth and maturation.
2 PAEDIATRIC EXERCISE PHYSIOLOGY
INTRODUCTION
Paediatric exercise science examines the acute and chronic responses of the child and
adolescent to exercise and/or physical activity. Morphological parameters and physi-
ological functions such as heart volume, lung function, aerobic power and muscular
strength develop with increasing age and body size. Furthermore, physical fitness
(e.g. muscular, motor and cardiorespiratory fitness) also changes with growth and
maturation. Therefore, variations in growth and maturation of a child can have pro-
found effects upon aspects of physical activity, physical fitness and physical perform-
ance. To fully understand paediatric exercise physiology a student needs a sound
understanding of the general principles of childhood growth and maturation, other-
wise termed auxology. This chapter outlines the basic concepts of growth and matura-
tion, and reviews some of the possible biological maturity indicators that can be used
to control for the confounding effects of growth and maturation.
The terms growth, biological maturation and development are often used synony-
mously in the paediatric literature. Although interrelated, the concepts have funda-
mental and semantic differences. Growth refers to changes in size of an individual,
as a whole or in parts. As children grow, they become taller and heavier, they increase
their lean and fat tissues, and their organs increase in size. Changes in size are a
result of three cellular processes: (1) an increase in cell number, or hyperplasia, (2) an
increase in cell size, or hypertrophy, and (3) an increase in intercellular substances, or
accretion. All three occur during growth but the predominance of one process over
another varies with chronological age and the tissue involved (Malina et al 2004).
Maturation has been described as the process of being mature, or progress toward
the mature state (Malina et al 2004). The process of maturing has two components,
timing and tempo. The former refers to when specific maturational events occur (e.g.
age when menarche is attained, age at the beginning of breast development, age at the
appearance of pubic hair, or age at maximum growth in height during the adolescent
growth spurt (peak height velocity; PHV)). Tempo refers to the rate at which matura-
tion progresses (i.e. how quickly or slowly an individual passes from the initial stages
of sexual maturation to the mature state). Maturation occurs in all biological systems
in the body but at different rates. Furthermore, the timing and tempo of maturity vary
considerably among individuals, with children of the same chronological age differing
dramatically in their degree of biological maturity.
Development refers to the acquisition of behavioural competence (the learning of
appropriate behaviours expected by society) and is culture specific. As children expe-
rience life at home, school, church, sports, recreation, and other community activities,
they develop cognitively, socially, emotionally, morally, and so on. Children and ado-
lescents learn to behave in culturally appropriate manners. Development can also
be thought of within the biological context. Here development refers to the processes
of differentiation and specialization occurring during the prenatal life. Apart from
during prenatal life, the term development is seen most frequently in the behavioural
literature and although an essential component it will not be covered in any detail in
this book.
It is important to recognize that growth, maturation, and development occur simul-
taneously and interact; however, they may not follow the same time line. Ayoung
person could be advanced in terms of social and emotional development but delayed
in biological maturation, or vice versa. In the growth and development literature, life
leading up to maturity is split into three stages: the prenatal period, childhood and
adolescence. The period of prenatal life is vitally important to the child’s well-being;
however, it will not be covered in this chapter, as discussion will focus on the first two