Presentation Package

1
chapter
16
Children and Adolescents in Sport and Exercise
2
Learning Objectives

• Understand the differences between the terms
  growth, development, and maturation
• Examine the processes by which bone, muscle, and
  fat mass increase in size with growth from birth
  to adulthood, how this relates to changes and
  rates of change in height and weight, and how
  these processes differ between boys and girls
• Learn how the nervous system matures as children
  grow, and how this might influence the
  development of balance, agility, and coordination

(continued)
3
Learning Objectives (continued)

• Find out how strength increases with age and what
  factors influence these changes
• Discover how children can safely improve their
  strength
• Learn how training improves aerobic and anaerobic
  capacities in prepubescent children
• To understand how these physiological changes
  with growth affect the motor ability and sports
  performance of the child and adolescent
• Examine the differences between children and
  adults with respect to thermoregulation

4
Terminology

• Growth an increase in the size of the body
  and/or of its parts
• Development the differentiation of cells along
  specialized lines of function (functional changes
  with growth)
• Maturation the process of taking on an adult
  form and becoming fully functional (defined by
  the system)
• Chronological age
• Skeletal age
• Stage of sexual maturation

5
Phases of Growth and Development

• Infancy first year of life
• Childhood age 1 to puberty
• Puberty development of secondary sex
  characteristics sexual reproduction becomes
  possible
• Adolescence puberty to completion of growth and
  development

6
Changes With Age in the Rateof Increase in
Height (cm/yr)
7
Height and Weight

• Key Points
• Growth in height is very rapid during the first 2
  years of life, with a child reaching 50 of adult
  stature by age 2
• The rate of growth is slower throughout childhood
  until a marked increase occurs near puberty
• The peak rate of height growth occurs at age 12
  in girls and 14 in boys
• Full height is typically achieved at age 16 in
  girls and 18 in boys
• Growth in weight follows the same trend as
  height, with the peak rate of weight increase
  occurring at age 12.5 in girls and 14.5 in boys

8
Bone Growth

• During growth, bone develops from cartilage
• Fibrous membranes and cartilage transform into
  bone by ossification
• Growth is completed when cartilage cells stop
  growing and growth plates are replaced by bone
  (by early 20s)
• Requires a rich blood supply to deliver essential
  nutrients
• Calcium is required to build and maintain bone
  strength
• Weight-bearing exercise increases bone width and
  density

9
Muscle Growth

• In boys, skeletal muscle mass increases from 25
  of body weight at birth to 40-45 in young men
• Muscle development rate peaks at puberty in boys
  corresponding with a 10-fold increase in
  testosterone
• In girls, skeletal muscle mass increases from 25
  of body weight at birth to 30-35 in young women
• Muscle development is slower in girls
• Muscle development primarily results from
  hypertrophy of existing fibers
• Muscle length increases with bone growth due to
  an increase in sarcomeres (added at the junction
  between the muscle and the tendon)

10
Growth and Fat Storage

• Fat cells form and fat deposition starts in fetal
  development
• Fat is stored by increasing the size and number
  of fat cells
• Fat storage depends on
• Diet
• Exercise habits
• Heredity
• At birth, 10-12 of total body weight is fat
• At maturity, fat content averages 15 of total
  body weight in males and 25 in females

11
Changes in Skinfold Thicknessin Boys and Girls

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

12
Changes in Percent Fat, Fat Mass,and Fat-Free
Mass for Females and MalesFrom 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.

13
Nervous System

• As children grow, they develop better balance,
  agility, and coordination
• Myelination of the nerve fibers must be completed
  for fast reactions and skilled movement
• Myelination of the cerebral cortex occurs most
  rapidly in childhood but continues well beyond
  puberty
• The full development of reaction speed and motor
  skills depends on completion of the myelination
  process

14
Tissue Growth and Development

• Key Points
• Muscle mass increases steadily along with weight
  gain from birth through adolescence
• In boys, the rate of muscle mass increase peaks
  at puberty, when testosterone production
  increases dramatically. Girls do not experience
  this sharp increase in muscle mass
• Muscle mass increases result primarily from fiber
  hypertrophy with little or no hyperplasia
• Muscle mass peaks in girls between ages 18-20,
  and in boys between 18-25, although it can be
  further increased through diet and exercise

(continued)
15
Tissue Growth and Development (continued)

• Key Points
• Fat cells increase in size and number throughout
  life
• The amount of fat accumulation depends on diet,
  exercise habits, and heredity
• At maturity, the bodys fat content averages 15
  in men and 25 in women
• Balance, agility, and coordination improve as
  childrens nervous systems develop
• Myelination of nerve fibers must be completed
  before fast reactions and skilled movements are
  fully developed

16
Strength

• Improves as muscle mass increases
• Peak strength occurs age 20 in women
• Peak strength occurs between ages 20-30 in men

17
Gains With Age in Leg Strengthof Young Boys
Followed LongitudinallyOver 12 Years

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

18
Changes in Strength With Developmental Status in
Boys and Girls

• Reprinted, by permission, from K. Froberg and O.
  Lammert, 1996, Development of muscle strength
  during childhood. In The child and adolescent
  athlete (London Blackwell Publishing Company),
  28.

19
Cardiovascular and Respiratory Function

• Resting and Submaximal Exercise
• Resting blood pressure is lower in children
  (proportional to body size), but progressively
  increases during the late teen years
• Blood flow to active muscles per unit volume of
  muscle is greater
• Stroke volume is lower in children (smaller
  hearts)
• Heart rate responses for a given absolute
  submaximal work rate is higher (to compensate for
  reduced SV)
• Cardiac output is somewhat lower for a given
  absolute work rate
• (a-v)O2 differences are increased to compensate
  for a lower cardiac output

20
Submaximal (a) Heart Rate, (b) Stroke Volume, (c)
Cardiac Output and (d) (a-v)O2 Difference in a
12-Year-Old Boy and Fully Mature Man
21
Cardiovascular and Respiratory Function

• Maximal Exercise
• Maximal heart rate is higher
• Lower maximal cardiac output
• Oxygen delivery limits performance
• Lung Function
• All lung volumes increase until growth is
  complete
• VEmax increases with age until physical maturity

.
22
Physiological Responsesto Acute Exercise

• Key Points
• Strength improves and muscle mass increases with
  age
• Gains in strength with growth also depend on
  neural maturation
• Blood pressure is directly related to body size
• Blood pressure is lower both at rest and during
  exercise in children vs. adults
• During both submaximal and maximal exercise, a
  childs smaller heart and blood volume result in
  a lower stroke volume vs. adults
• A childs heart rate is higher than an adults
  for the same rate of work or VO2

.
(continued)
23
Physiological Responsesto Acute Exercise
(continued)

• Key Points
• A child's cardiac output is less than an adults
• During submaximal exercise there is an increase
  in (a-v)O2 difference to ensure adequate oxygen
  delivery
• At maximal work rates, oxygen delivery limits
  performance
• Lung volumes increase until physical maturity,
  primarily because of increasing body size
• Until physical maturity, maximal ventilatory
  capacity and maximal expiratory ventilation
  increase in direct proportion to the increase in
  body size

24
Metabolic Function in Children

• Aerobic Capacity
• In boys, VO2max peaks between ages 17-21
• In girls, VO2max peaks between ages 12-15
• Little difference between children and adults if
  normalized for differences in body size
• Running Economy
• Economy is lower in children and improves with
  growth (increased stride frequency)

.
.
25
Changes in Maximal Oxygen Uptake With Age
26
Metabolic Function in Children

• Anaerobic Capacity
• Ability to perform anaerobic activities is
  limited
• Resting concentrations of ATP and PCr are similar
  to adults
• Children have lower glycolytic capacities
• Lower lactate concentrations in the blood and
  muscle at maximal and supramaximal rates of work
• Children have lower RERs during maximal exercise
  bouts, suggesting less lactate production
• Anaerobic mean and peak power outputs are lower
  in children, even when scaled for body mass

27
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.

28
Development of Aerobic and Anaerobic
Characteristics in Boys and GirlsAges 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).

29
Physiological Adaptationsto Training Body
Composition

• With both resistance and aerobic training, boys
  and girls will
• ? Weight and fat mass
• ? Fat-free mass (attenuated compared with
  adolescents and adults)
• ? Bone growth (bone mineral density)

30
Physiological Adaptationsto Training Strength

• With resistance training, boys and girls will
• ? Muscle strength (dependent on volume and
  intensity of training)
• Strength gains are accomplished without much
  change in muscle size, indicating increased motor
  unit activation (neural adaptations)

31
(continued)
32
(continued)
33
Physiological Adaptationsto Training Aerobic
Capacity

• Following aerobic training, children have
• Small ? in aerobic capacity in prepubescent
  children
• Larger ? in aerobic capacity in adolescents
• Differences appear to depend on heart growth

34
Physiological Adaptationsto Training Anaerobic
Capacity

• Following anaerobic training, children have
• ? Resting concentrations of PCr, ATP, and
  glycogen
• ? Phosphofructokinase activity
• ? Maximal blood lactate concentrations

35
Physiological Adaptations to Training

• Key Points
• Body composition changes with training in
  children and adolescents are similar to those
  seen in adults
• The risk of injury from resistance training in
  young athletes is relatively low
• Strength gains are achieved from resistance
  training in children primarily from neurological
  adaptations with little change in muscle size
• Aerobic training in preadolescents does not alter
  VO2max as much as would be expected from the
  training stimulus (heart size)

.
(continued)
36
Physiological Adaptations to Training (continued)

• Key Points
• Endurance performance improves with aerobic
  training in preadolescents
• A childs anaerobic capacity increases with
  anaerobic training
• In general, growth and maturation rates and
  processes are probably not altered significantly
  by training

37
Motor Ability and Sport Performance

• Performance generally increases with age
• Development of neuromuscular and endocrine
  systems
• Increased activity

38
Changes in Motor Abilities From the Ages of 6-17
Years
(continued)
Data from the Presidents Council on Physical
Fitness and Sports, 1985.
39
Changes in Motor Abilities From the Ages of 6-17
Years (continued)
Data from the Presidents Council on Physical
Fitness and Sports, 1985.
40
U.S. National Record Performances for Boys and
Girls
41
Thermal Stress and Children

• Children rely more on convection and radiation,
  which are enhanced through greater peripheral
  vasodilation
• Evaporative heat loss is lower because of reduced
  sweat rates
• Children have greater ratios of surface area to
  mass
• Acclimatization to heat is slower in boys than in
  adult men (no data available for girls)
• Conductive heat loss is greater in the cold,
  increasing risk for hypothermia
• Exercising in extreme temperatures should be
  minimized (limited data available)