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
CHILDREN AND ADOLESCENTS IN SPORT AND EXERCISE
w Find out why absolute aerobic and cardiorespiratory endurance capacity increases from age 6 to age 20.
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.
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.
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
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
RATE OF INCREASE IN HEIGHT AND WEIGHT
Bone Ossification: Transformation from Cartilate to Bone
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
Fractures of the epiphyseal plate
wDisrupts the blood supply
wDisrupts growth, which can lead to limb length discrepancies
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
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
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
Skinfold Thickness: an Estimate of Fatness
CHANGES IN FAT AND FAT-FREE MASS
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.
Physiological Responses to Exercise
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
STRENGTH GAINS WITH AGE
These data are for boys only.
Composite Strength Changes with Development
PHV = peak height velocity
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
HR and SV as a Function of Oxygen Uptake
Q and a-vO2 as a Function of Oxygen Uptake
w Maximal stroke volume and Qmax are lower in children than in adults.
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.
w VEmax increases with age until physical maturity at which point it begins to decrease with age.
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.
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.
CHANGES IN VO2MAX WITH AGE
Absolute (i.e., l/min) Relative to body weight (i.e., ml/kg/min)
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
OPTIMAL ANAEROBIC POWER OUTPUT
Aerobic and Anaerobic Capacities as a % of Adult Levels
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
Theoretical Model for Strength Development for Boys
How would the model differ for girls?
w Aerobic training improves cardiorespiratory endurance performance in children, but the changes in VO2max are less than expected.
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.
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.
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.
Changes in Motor Ability with Age
Age Group U.S. National Swimming Records
Age Group U.S. National Track Records
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.