Children and Exercise XXVIII

The Proceedings of the 28th Pediatric Work Physiology Meeting

Manuel Coelho-E-Silva, Neil Armstrong, Manuel Coelho-E-Silva, Amândio Cupido-dos-Santos, António J. Figueiredo, José P. Ferreira, Neil Armstrong

• Publisher: Routledge
• Year: 2013
• ISBN:
  9781134115853
• Edition: 1
• Topic: Medicine
• Subtopic: Pediatric Medicine

Children and Exercise XXVIII presents the latest scientific research into paediatric exercise physiology, endocrinology, kinanthropometry, growth and maturation, and youth sport. Including contributions from a wide-range of leading international experts, the book is arranged into seven thematic sections addressing:

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• Cardiovascular responses to exercise

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• Genetics, metabolism and physical activity

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• Limiting factors of muscle exercise

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• Respiratory responses to exercise

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• Epidemiology in physical activity and obesity

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• Physical activity and nutrition

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• Metabolic disorders and exercise

Offering critical reviews of current topics and reports of current and on-going research in paediatric health and exercise science, this is a key text for all researchers, teachers, health professionals and students with an interest in paediatric sport and exercise science, sports medicine and physical education.

Part I

The Josef Rutenfranz Lecture

THE JOSEF RUTENFRANZ LECTURE

Professor Dr Josef Rutenfranz was the leader of the group of eight scientists who conceived PWP in a café in Berlin in 1967, and organized the first PWP symposium in Dortmund in 1968. Josef Rutenfranz chaired the first meeting and remained the unofficial “Chairman of the Board” until his untimely death at the age of 60, on 28^th February 1989. At PWP 1989, in Hungary, later that year it was decided that subsequent PWP symposia should begin with the Josef Rutenfranz Lecture.

1991	Per-Olaf Astrand	Children and Adolescents: Performance Measurements, Education
1993	Dan M. Cooper	New Horizons in Paediatric Exercise Research
1995	Oded Bar-Or	Safe Exercise for the Child with a Chronic Disease
1997	Han C. G. Kemper	A Scientific Voyage through Research in Children’s Health – From Heart via Muscle to Bone
1999	Frank Galioto	The Challenges of the Future: Are We Ready?
2001	Anna Farkas	What About Girls?
2003	Gaston Beunen	Physical Growth, Maturation and Performance: Back to the Future
2005	Beat Villiger	News on Exercise-Induced Asthma
2007	Willem Van Mechelen	A Behavioural and Ecological Perspective to Energy-Balance-Related Behaviours in Children
2009	Emmanuel Van Praagh	The Child as a Source of Mechanical Power
2010	Viswanath Unnithan	Preventive Efficacy of Team Sports: Cardiovascular and Cardio-Respiratory Insights for Health and Performance
2011	Neil Armstrong	From Playground to Podium
2013	Robert M Malina	Youth, Sport, and Physical Activity

CHAPTER NUMBER 1

YOUTH, SPORT, AND PHYSICAL ACTIVITY

Robert M. Malina

University of Texas at Austin and Tarleton State University, USA

Several key topics in the long history of paediatric work physiology research are highlighted in the title. Youth are the children and adolescents who are the focus of research. Sport is perhaps the most popular and visible context of physical activity (PA) among youth. PA is a topic of heightened public health interest. Organized youth sports are a major feature of the lives of children and adolescents in many parts of the world, and are driven largely by adults – administrators, coaches and parents.

Paediatric work physiology has evolved from a largely physiological focus into a variety of disciplines highlighting interactions of biology and behaviour in the context of physical activity and sport from laboratory to the playing field to the clinic. This overview evaluates (1) trends in PA, physical fitness (PF) and associated factors among youth in the past 50 years or so, and (2) trends and issues in organized youth sport, and then attempts to relate the two. Primary focus is on data for the U.S., though data from other countries are cited where appropriate.

1.1 TRENDS IN PHYSICAL ACTIVITY

Productivity statistics for agriculture and manufacturing suggest a decline in physically demanding work in the U.S. Estimated hours of work required to produce 100 bushels of corn or wheat declined by about 75% between 1900 and 1950, and then by 91% for corn and 70% for wheat between 1950 and 1980. Weekly hours in manufacturing work declined by 30% between 1900 and 1950, but did not change between 1950 and 2000 (Floud et al., 2011). Improvements in agricultural and industrial technologies contributed to more efficient production and reduced physical activity demands.

The shift to less physically demanding occupations was more apparent over the past two generations. Moderate intensity occupations (≥3 METS) in U.S. adults decreased from about 48% in 1960 to 20% in 2008 while light intensity (2.0-2.9 METS) and sedentary (< 2 METS) occupations increased over this interval from 37% to 55% and from 15% to ∼25%, respectively. Mean occupation-related energy expenditure also decreased by about 100 calories per day (Church et al., 2011). Estimated weekly time in occupational and home/domestic work, work-related travel and active leisure among U.S. adults declined from 235 to 160 MET hours/week (32%) between 1965 and 2009, while time sedentary increased, ∼25 to 37 hours/week. Estimates for U.K adults between 1961 and 2005 indicated a, decline in physical activity from 216 to 173 MET hours/week (20%) and an increase in time sedentary from 27 to 42 hours/week (Ng and Popkin, 2012).

Corresponding estimates for earlier samples of youth are not available. Many youth were engaged in agricultural and manufacturing work early in the twentieth century, while boys in “street” occupations (errands/delivery, newspapers, shoeshine) were quite active. Lower heart rates, for example, were noted in boys with a newspaper route; their “efficiency” was attributed to regular activity: the boys covered 3 to 9 miles daily delivering papers (McCurdy, 1913).

Estimates of daily energy expenditure (EE) among students at a boarding school in the U.K. in 1919–1921 provide early insights (Bedale, 1922–1923). The Douglas bag technique was used; BMR was measured in bed. Energy costs of school and non-school activities (walking, sports, outdoor work, gardening, haymaking, etc.) were derived and total daily EE on “typical school days” was estimated. Estimated costs of some activities in younger students were based on observation. Results are summarized in Table 1.1.

EE (total, per unit mass) based on heart rate (HR, some with calorimetry) and doubly labeled water (DLW) in contemporary youth are included for comparison. HR estimates date to the 1980s and DLW to the 1990s. Allowing for age and methodological variation, EE is lower in all samples compared to the estimates from ∼1920 (except boys 14-18 years, DLW). EE is related to body size; trends must be viewed in context of secular gains in body mass compared to youth of 3–4 generations ago. Estimated absolute and relative EE (HR) declined between ∼1920 and the 1980s; HR estimates also suggested a continued decline in relative EE from the 1990s to the present in boys and girls <14 years of age. DLW estimates suggested a decline in relative EE between ∼1920 and the 1990s, but no subsequent changes.

The most variable component of EE is PA (AEE). The prevalence of Canadian youth 12–14 and 15–19 years with leisure time AEE ≥ 3 and ≥ 6 kcal/kg/day (questionnaire) increased between 1981 and 1988 in only boys, but did not change appreciably between 1988 and 1998 in both sexes (Eisenmann et al., 2004). About 20% of boys in both age groups and girls 12–14 years and 10% of girls 15–19 years exceeded the AEE recommendation for youth (≥ 6 kcal/kg/day) in 1998.

In contrast to EE, PA is a behaviour and contexts of PA are variable. Estimates of PA based on questionnaires and diaries are subjective. Accelerometry is objective, but there is a need to relate accelerometry to specific contexts of PA. Both subjective and objective estimates of PA show a decline in PA from late childhood through adolescence, although there is variation among studies, contexts and scales. Boys are more active than girls, on average; the sex difference is attenuated during adolescence if data are expressed relative to maturation rather than chronological age (Thompson et al., 2003). Current emphasis is largely focused on levels of PA associated with health benefits; the current recommendation for school age youth is ≥60 minutes of moderate-to-vigorous PA (MVPA) daily (Strong et al., 2005).

Table 1.1 Estimated energy expenditure (EE) in youth: 1920–2011.

* Data for 1919–1921 are calculated from Bedale (1922–1923); others are means weighted for sample sizes of individual studies (Malina, unpublished); HR=heart rate, includes calorimetry; DLW=doubly labeled water. Studies are grouped by year of publication.

It is often assumed that levels of habitual PA of children and adolescents have declined over time. Data addressing this issue, however, are limited in time depth. Self-reported PA and variable criteria for levels of PA have also been used and data are limited to adolescents. The Youth Risk Behavior Survey (YRBS) is a major source of data for American high school youth. A slight decline was noted in physically active boys (“exercise and sports activities that make you sweat and breathe hard for 20 minutes or more on three or more days in the past week”) between 1993 and 2003, 75% to 70%, but not in girls, 56% to 55% (Adams, 2006). In contrast, no change was noted in percentages of boys and girls reporting moderate PA (did not make students sweat or breathe hard) and vigorous PA (made students sweat or breathe hard) between 1993 and 2005 (Li et al., 2010). Moderate PA did not appreciably differ between boys (29%) and girls (24%), while vigorous PA was higher in boys (72%–75%) than girls (56%). Guidelines in the U.S. have since been modified to include both aerobic (≥60 minutes per day, 7 days per week) and muscle strengthening (≥3 days per week) activities (US Department of Health and Human Services, 2010). In the 2010 National Youth Physical Activity and Nutrition Study, small percentages of boys (22%) and girls (8%) met the aerobic criteria (“increased your heart rate and made you breathe hard for some of the time”), while more youth (boys 65%, girls 37%) met the muscle strengthening criteria (“such as push-ups, sit-ups, or weight lifting”). Only 19% of boys and 26% of girls met the criteria for both. Results for muscle strengthening were similar to the 2003 YRBS while those for aerobic acti...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface
• Acknowledgments
• Part I: The Josef Rutenfranz Lecture
• Part II: Keynote Lectures
• Part III: Physiology
• Part IV: Neuromuscular Issues
• Part V: Cardiovascular and Cardiorespiratory Fitness
• Part VI: Physical Fitness and Health
• Part VII: Physical Activity and Sedentary Behaviour
• Part VIII: Sport Participation and the Young Athlete