16

Children and Adolescents in Sport and Exercise

chapter

Terminology

Growth is an increase in the size of the body or its parts.

Development is the functional changes that occur with growth.

Maturation is the process of taking on an adult form and becoming functional.• Chronological age• Skeletal age• Stage of sexual maturation

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

Adolescence—puberty to completion of growth and development

RATE OF INCREASE IN HEIGHT AND WEIGHT

Bone Growth

• Is complete when cartilage cells stop growing and epiphyseal plates are replaced by bone (by early 20s)

• Requires rich blood supply to deliver essential nutrients• Requires calcium to help build and maintain strength• Slows or breaks down when blood calcium levels are

too low• Is helped by exercise, which affects bone width,

density, and strength

Bone Injuries and Growth

Fractures of the Epiphyseal Plate• Change blood supply• Disrupt growth, which can lead to discrepancies in

limb length

Traumatic Epiphysitis• Inflammation of epiphysis• Can lead to separation of epiphysis• If caught early, can be treated without permanent

damage

Muscle Growth

• Results primarily from hypertrophy of existing fibers• Muscle length increases with bone growth due to

increase in sarcomeres• Boys’ muscle mass peaks at 50% of body weight at 18

to 25 years• Girls’ muscle mass peaks at 40% of body weight at 16

to 20 years

Growth and Fat Storage

• Fat is stored starting at birth.• Fat is stored by increasing the size and number of fat

cells.• Fat storage depends on diet, exercise habits, and

heredity.• At maturity, fat content averages 15% in males and

25% in females.

Changes in Skinfold Thickness in Boys and Girls

Data from NHANES-I, National Center for Health Statistics.

Changes in Percent Fat, Fat Mass, and Fat-Free Mass for Females and Males

From Birth to 20 Years of Age

Reprinted, by permission, from R.M. Malina, C. Bouchard, and O. Bar-Or, 2004, Growth, maturation, and physical activity, 2nd ed. (Champaign, IL: Human Kinetics), 114.

Key Points

Tissue Growth and Development• Girls mature physiologically about 2 to 2.5 years

earlier than boys do.• Bones are formed through an ossification process,

which is usually complete by one’s early 20s.• Injury of a bone’s epiphysis could cause delays in its

growth.• Muscle growth occurs primarily at puberty due to

hypertrophy and increases in sarcomere length.

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Key Points (continued)

Tissue Growth and Development• Fat storage occurs due to increases in the size and

number of fat cells.• Fat storage starts at birth and is influenced

throughout life by diet, exercise, and heredity.• Balance, agility, and coordination improve as

children’s nervous systems develop.• Myelination of nerve fibers—which speeds the

transmission of impulses—is necessary before fast reactions and skills are fully developed.

Physical Performance and Maturation

• Motor ability increases.• Strength increases.• Lung volume and peak flow increase.• Blood pressure, heart size, and blood volume increase.• Heart rate decreases.• Aerobic and anaerobic capacities and running economy

increase.• Heat and cold tolerance increases.

Gains With Age in Leg Strength of Young Boys Followed Longitudinally

Over 12 Years

Data from H.H. Clarke, 1971, Physical and motor tests in the Medford boys' growth study (Englewood Cliffs, NJ: Prentice-Hall).

Changes in Strength With Developmental Status in Boys and Girls

Key Points

Pulmonary Function and Growth• As body size increases, lung size and lung

function increase.• Lung volume and peak flow increase until growth

is complete.• VEmax increases with age until physical maturity, at

which point it begins to decrease with age.• Boys’ absolute lung volumes and peak flow values

are higher than girls’ absolute values due to girls’ smaller body size.

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Submaximal Exercise and Growth

Blood Pressure• Lower in children but progressively increases to

adult levels in later teens.• Larger body size results in higher blood pressure.

Cardiovascular Function• Smaller heart size and total blood volume of

children result in a lower stroke volume.• Heart rate response is higher than in adults at a

given rate of submaximal work.• Lower cardiac output than in adults.• Higher a-vO2 difference than in adults.-

Key Points

Maximal Exercise and Growth• HRmax is higher in children but decreases linearly with

age.• Maximal stroke volume and Qmax are lower in children

than in adults.• Lower oxygen delivery capacity limits performance at

high absolute rates of work.• At relative rates of work (moving own body weight),

oxygen delivery capacity does not limit performance.

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Key Points (continued)

VO2max and Growth• VO2max peaks around age 17 to 21 in males and

decreases linearly with age.• VO2max 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.

• Absolute VO2max is lower in children than in adults at similar training levels.

• When VO2max is expressed relative to body weight, there is little difference in aerobic capacity between adults and children.

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Changes in Maximal Oxygen Uptake With Age

Anaerobic Capacity in Children

• Ability to perform anaerobic activities is lower.• Glycolytic capacity is lower.• They produce less lactate and cannot attain high RER

values during maximal exercise.• Anaerobic mean and peak power outputs are lower.

Optimal Peak Power Output (Anaerobic Power) Adjusted for Body Mass in

Preteenagers, Teenagers, and Adults

Data from A.M.C. Santos et al., 2002, "Age- and sex-related differences in optimal peak power," Pediatric Exercise Science 14: 202-212.

Development of Aerobic and Anaerobic Characteristics in Boys and Girls

Ages 9 to 16 Years

Adapted, by permission, from O. Bar-Or, 1983, Pediatric sports medicine for the practitioner: From physiologic principles to clinical applications (New York: Springer-Verlag).

Thermal Stress and Children

• Evaporative heat loss is lower because the sweat glands produce less sweat.

• Acclimatization to heat is slower in boys than in adult men.

• Conductive heat loss is greater, increasing risk for hypothermia.

• Exercising in extreme temperatures should be minimized.

Resistance Training in Preadolescents

• May protect against injury and help build bones• Improves motor skill coordination• Increases motor unit activation• Results in other neurological adaptations• Causes little change in muscle size

Key Points

Training the Young Athlete• Training programs for children should be conservative

to reduce the risk of injury, overtraining, and loss of interest in the sport.

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

• Aerobic training improves endurance performance in children (though not VO2max).

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Key Points (continued)

Training the Young Athlete• Anaerobic capacity increases with aerobic training.• Regular training typically results in decreased total

body fat, increased fat-free mass, and increased total body mass.

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