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)
Phases of Growth
and Development
Infancy:
first year of life
Childhood:
age 1 to puberty
Puberty:
development of secondary sex
characteristics
Adolescence:
puberty to completion of growth
and development
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
Muscle Growth
In boys, skeletal muscle mass increases from 25% of
body weight at birth to ~40-45% in young men, ~30-
35% in young women
Muscle development rate peaks at puberty in boys
corresponding with a ~10-fold increase in
testosterone
Muscle development is slower in girls
Muscle development results primarily 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)
Fat Growth and 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
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
Strength
Improves as muscle mass increases
Peak strength occurs ~ age 20 in women
Peak strength occurs between ages 20-30 in men
Cardiovascular and
Respiratory Function
Resting and submaximal exercise:
-Resting blood pressure is lower in children, but
progressively increases during the late teen years
-Stroke volume is lower in children
-Heart rate responses for a given absolute submaximal
work rate is higher
-Cardiac output is somewhat lower for a given absolute
work rate
-Blood flow to active muscles per unit volume of muscle is
greater
-(a-v)O2 differences are increased to compensate for a
lower cardiac output
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
Metabolic Function
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
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
Endocrine Responses
and Substrate Utilization
Endocrine responses:
-Exercising growth hormone and insulin-like growth
factor surge ? than in adults
-? Stress response to exercise compared to adults
-Hypoglycemic at exercise onset
-Immature liver glycogenolytic system
Substrate utilization:
-Relies more on fat oxidation compared to adults
-Exogenous glucose utilization high
Physiological Adaptations
to 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)
Physiological Adaptations
to Training: Strength
With resistance training, boys and girls will:
-? Muscle strength
-Strength gains are accomplished without much change
in muscle size, indicating increased motor unit
activation
-Might offer protection against injury
Physiological Adaptations
to 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
Physiological Adaptations
to Training: Anaerobic Capacity
Following anaerobic training, children have:
-? ResFng concentraFons of PCr, ATP, and glycogen
-? Phosphofructokinase actvity
-? Maximal blood lactate concentraFons
Motor Ability and Sport Performance
Performance generally increases with age
-Development of neuromuscular and endocrine
systems
-Increased activity
Plateaus earlier in girls
-Estrogen
-Muscle mass
-Sedentary lifestyle
Thermal Stress and Children
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Special Issues
Growth with training:
-Little or no negative effect on height
-Affects weight, body composition with intensity
-Peak height velocity age unaffected
-Rate of skeletal maturation unaffected
Maturation with training: effects on markers of
sexual maturation less clear