chapter
16
Children and
Adolescents in
Sport and
Exercise
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 FatFree 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.
(continued)
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.
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-vO
2 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.
(continued)
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.
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).
(continued)
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.