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C H A P T E R 16. CHILDREN AND ADOLESCENTS IN SPORT AND EXERCISE. w Find out why absolute aerobic and cardiorespiratory endurance capacity increases from age 6 to age 20. (continued). Learning Objectives.

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C H A P T E R 16

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C h a p t e r 16

C H A P T E R 16


C h a p t e r 16

w Find out why absolute aerobic and cardiorespiratory endurance capacity increases from age 6 to age 20.


Learning Objectives

w Find out at what age height and weight reach its peak rate of growth in boys and girls.

w Learn what changes occur with maximal and submaximal heart rate and pulmonary function and with growth.

w Discover how growth affects stroke volume and cardiac output at fixed rates of work.

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Learning Objectives

w Learn how training improves aerobic and anaerobic capacities in prepubescent children.

w Discover how children can improve their strength safely.

w Review the effects of physical activity and regular training on a child’s growth and maturation.

w Examine the differences between children and adults with respect to thermoregulation.

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Maturation—process of taking on the adult form and function – measured or expressed in different ways:

w Chronological age

w Skeletal age

w Stage of sexual maturation


Growth—an increase in the size of the body or its parts

Development—the functional changes that occur with growth

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Phases of Growth and Development

Infancy—first year of life

Childhood—age 1 to puberty

Puberty—development of secondary sex characteristics and capability of sexual reproduction; usually 8-12 years old

Adolescence—puberty to completion of growth and development

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Bone Ossification: Transformation from Cartilate to Bone

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Bone Growth

wIs complete when cartilage cells stop growing and epiphyseal plates are replaced by bone (by early 20s; varies from pre-teens to mid-20s; 2-3 yrs earlier in girls)

wRequires rich blood supply to deliver essential nutrients

wRequires calcium to build and maintain strength; vitamin D promotes calcium absorption from the small intestine during digestion

wGrowth slows when blood calcium levels are too low; can lead later in life to osteoporosis

wIs helped by gravity-resisting exercise, which loads the bone, affecting bone width, density, and strength

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Fractures of the epiphyseal plate

wDisrupts the blood supply

wDisrupts growth, which can lead to limb length discrepancies

Traumatic epiphysitis

wInflammation of epiphysis from overuse (pitchers)

wCan lead to separation of epiphysis

wIf caught early it can be treated without permanent damage

Bone Injuries and Growth

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Muscle Growth

wResults primarily from hypertrophy of existing fibers due to increase in myofilaments and myofibrils

wMuscle length increases with bone growth due to increase in the number of sarcomeres in series

wBoys’ muscle mass peaks at about 50% of body weight at 18 to 25 years

wGirls’ muscle mass peaks at about 40% of body weight at 16 to 20 years

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Growth and Fat Storage

wFat is stored starting at birth

wFat is stored by increasing the size and number of fat cells, but cells can only increase to a certain maximum volume and then new cells are formed

wFat storage depends on diet, exercise habits, and heredity

wAt maturity, fat content averages about 15% in males and about 25% in females

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Skinfold Thickness: an Estimate of Fatness

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Key Points

Tissue Growth and Development

wGirls mature physiologically about 2 years earlier than boys

w Balance, agility, and coordination improve as children’s nervous systems develop.

w Myelination of neurons in the cerebral cortex—which speeds the transmission of impulses in those neurons—is necessary before fast reactions and skills are fully developed. This is usually not completed until during adolescence.

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Physiological Responses to Exercise

wStrength increases

wGains in strength with growth also depend on neural maturation because neuromuscular control is limited until myelination is complete, usually around sexual maturity.

wBlood volume, heart size, and blood pressure increase

wHeart rate decreases

wAerobic and anaerobic capacities and running economy increase

wLung volume and peak flow increase

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These data are for boys only.

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Composite Strength Changes with Development

PHV = peak height velocity

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Blood pressure

wLower in children but progressively increases to adult levels in later teens

wLarger body size results in higher blood pressure

Cardiovascular function at a given oxygen uptake

wSmaller heart size and total blood volume of children result in a lower stroke volume

wHeart rate response is higher than adults at given rate of submaximal work

wLower cardiac output than adults

wTherefore, a higher a-vO2 diff than adults

Submaximal Exercise and Growth

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HR and SV as a Function of Oxygen Uptake

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Q and a-vO2 as a Function of Oxygen Uptake

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w Maximal stroke volume and Qmax are lower in children than in adults.

Key Points

Maximal Exercise and Growth

wHRmax is higher in children but decreases linearly with age.

w Lower oxygen delivery capacity (blood volume and pump capacity) limits performance at high absolute rates of work.

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w VEmax increases with age until physical maturity at which point it begins to decrease with age.

Key Points

Lung Function and Growth

wAs body size increases, lung size and lung function increase.

w Lung volumes and peak flow increase until growth is complete.

w Boys' absolute lung volumes and peak flow values are higher than girls' absolute values due to girls’ smaller body size.

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wVO2max (L/min) peaks around age 17 to 21 in males and then decreases linearly with age.


w VO2max (L/min) has been shown to peak around age 12 to 15 in females, though the decrease after age 15 may be due to females tending to reduce physical activity.


w Absolute VO2max (L/min) is lower in children than adults at similar training levels.


w When VO2max is expressed relative to body weight, there is little difference in aerobic capacity between adults and children, thus, additional muscle mass increases maximal oxygen consumption.

Aerobic Capacity in Children

w Relative to body weight, running economy is lower inchildren compared to adults.

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Absolute (i.e., l/min) Relative to body weight (i.e., ml/kg/min)

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Anaerobic Capacity in Children

wAbility to perform anaerobic activities is lower than in adults

wGlycolytic capacity (i.e., glycolytic enzyme levels) is lower

wProduce less lactate and cannot attain as high RER values during maximal exercise as adults

  • Anaerobic mean and peak power outputs are lower than in adults, even when scaled for body mass

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Aerobic and Anaerobic Capacities as a % of Adult Levels

Adult Level

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Resistance Training in Preadolescents

w May protect against injury and help build bones

w Improves motor skill coordination

w Increases strength largely through increased neural activation of motor units

w Causes little change in muscle size (i.e., little hypertrophy) and is considered safe if not overdone

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Theoretical Model for Strength Development for Boys

How would the model differ for girls?

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w Aerobic training improves cardiorespiratory endurance performance in children, but the changes in VO2max are less than expected.



Key Points

Training the Young Athlete

wTraining programs for children should be conservative to reduce the risk of injury, overtraining, and loss of interest in the sport.

w An appropriate resistance training program is relatively safe for children.

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Key Points

Training the Young Athlete

wAnaerobic capacity increases with anaerobic training.

w Regular training typically results in decreased total body fat, increased fat-free mass, and increased total body mass.

w Generally, training does not appear to significantly alter growth and maturation rates.

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Motor Ability and Sport Performance

wMotor ability in boys generally increases for the first 18 years of life, although in girls it tends to plateau around puberty.

wSports performance improves dramatically through childhood and adolescence.

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Changes in Motor Ability with Age

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100-m freestyle

400-m freestyle

Age Group U.S. National Swimming Records

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100-m run

1,500-m run

Age Group U.S. National Track Records

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Thermal Stress and Children

wEvaporative heat loss is lower due to less sweat produced by sweat glands.

wAcclimatization to heat is slower in boys than adult men; this presumably is also true in girls.

wConductive heat loss and gain is greater because of the child’s greater ratio of body surface area to mass, increasing risk for hypothermia in cold environments and hyperthermia in extremely hot environments (i.e., when environmental temperature is higher than body temperature).

wExercising in extreme temperatures, both hot and cold, should be minimized in children.

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