Transcript Slide 1

Children and Adolescents
in Sport and Exercise
CHAPTER 17 Overview
• Growth, development, and maturation
• Body composition
• Physiological responses to acute exercise
• Physiological adaptations to training
• Motor ability and sport performance
• Special issues
Growth,
Development, and Maturation
• Growth: increase in body or body part size
• Development: differentiation, functional
changes
• Maturation: process of taking adult form
– Chronological age
– Skeletal age
– Stage of sexual maturation
Growth,
Development, and Maturation
• Infancy: first year of life
• Childhood: first birthday to puberty
• Puberty: secondary sex characteristics
develop
• Adolescence: puberty to growth completion
Body Composition:
Growth and Development of Tissues
• Rates of change in height and weight
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Birth to 2 years: fast
2 years to just before puberty: slow
Puberty onset: fast
Midpuberty to late teens: slow
• Height and weight change not synchronized
– Height change fastest at 12 years (girls), 14 years
(boys)
– Weight change fastest at 12.5 years (girls), 14.5
years (boys)
Figure 17.1
Body Composition:
Growth and Development of Tissues
• Bone ossification from fetus to adulthood
– Growth plate: cartilage line in bone
– Growth plate closure = ossification completed
• Estrogen stimulates plate closure
– Girls achieve full bone maturity faster
– Midteens versus later teens/early 20s for boys
• Calcium essential for bone health
– Bone mineral density (BMD)
– Osteoporosis later in life
Figure 17.2
Body Composition:
Growth and Development of Tissues
• Muscle mass steadily increases with weight
– 25% of body weight at birth
– 30 to 35% of body weight in young women
(estrogen)
– 40 to 45% of body weight in young men
(testosterone)
– Peaks at 16 to 20 years (girls), 18 to 25 years (boys)
• Fiber hypertrophy   muscle mass
• More/longer sarcomeres   muscle length
Body Composition:
Growth and Development of Tissues
• Fat deposits form in fetus and throughout
life. Affected by
– Diet (changeable)
– Exercise habits (changeable)
– Heredity (not changeable)
• Percent body fat changes with age
– Birth: 10 to 12%
– At physical maturity—women: 25%, men: 15%
Figure 17.3
Body Composition:
Growth and Development of Tissues
• Neurological development in childhood
– Better balance, agility, coordination
– Due to ongoing myelination of nerves, brain
• Myelination also influences strength
Physiological Responses
to Acute Exercise
• Strength
• Cardiovascular, respiratory function
• Metabolic function
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Aerobic capacity
Running economy
Anaerobic capacity
Substrate utilization
Physiological Responses
to Acute Exercise
• Strength  as muscle mass  with age
– Peaks at ~20 years for women
– Peaks at 20 to 30 years for men
• Strength, power, skill require myelination
– Peak performance requires neural maturity
– Boys experience marked change at ~12 years
– Girls more gradual, linear changes
Figure 17.4
Figure 17.5
Physiological Responses
to Acute Exercise
• Resting and submaximal blood pressure
– Lower than in adults (related to body size)
– Smaller hearts, lower peripheral resistance during
exercise
• Resting and submaximal stroke volume, HR
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Lower SV: smaller heart, lower blood volume
Higher HR: almost compensates for low SV
Slightly lower cardiac output than an adult
(a-v)O2 difference will  to further compensate
Figure 17.6a
Figure 17.6b
Figure 17.6c
Figure 17.6d
Physiological Responses
to Acute Exercise
• Maximal HR higher than in adults
• Maximal SV lower than in adults
• Maximal cardiac output lower
– Limits performance: less O2 delivery
– Not a serious limitation for relative workloads
Physiological Responses
to Acute Exercise
• Lung function
– Lung volume increases with age
– Peak flow rates increase with age
– Postpuberty: girls’ absolute values lower than boys’
due to smaller body size
• Metabolic function
– Increases with age
– Related to muscle mass, strength, cardiorespiratory
function
Physiological Responses
to Acute Exercise
• Cardiorespiratory changes during exercise
accommodate muscles’ need for O2
• Cardiorespiratory changes with age permit
greater delivery of O2
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VO2max in L/min  with age (boys, girls)
VO2max in ml/kg/min steady with age in boys
VO2max in ml/kg/min  with age in girls
L/min more appropriate during growth year
Figure 17.7
Physiological Responses
to Acute Exercise
• Children’s economy of effort worse than
adults’
– Child’s O2 consumption per kilogram > adult’s
– With age, skills improve, stride lengthens
• Endurance running pace  with age
– Purely result of economy of effort
– Occurs regardless of VO2max changes, training
status
Physiological Responses
to Acute Exercise
• Children limited anaerobic performance
compared to adults
• Lower glycolytic capacity in muscle
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Less muscle glycogen
Less glycolytic enzyme activity
Blood lactate lower
Mean and peak power increase with age
• Resting stores of ATP-PCr similar to adults’
Figure 17.8
Figure 17.9
Physiological Responses
to Acute Exercise
• 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 Exercise Training
• Children’s acute responses differ from
adults’
• Training needs differ, too
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Body composition
Strength
Aerobic capacity
Anaerobic capacity
Physiological Adaptations
to Exercise Training
• Body weight and composition
– Respond to physical training similarly to adults
– Training   body weight/fat mass,  FFM
– Significant bone growth
• Childhood obesity
– Excessive portion sizes
– Calorie-dense foods
– Sedentary lifestyle
Physiological Adaptations
to Exercise Training
• Strength training historically controversial
• Weight lifting safe and beneficial
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Should be prescribed, supervised
Low risk of injury
Protects against injury
Child: strength gains only via neural mechanisms,
no hypertrophy
– Adolescent: neural + hypertrophy
Physiological Adaptations
to Exercise Training
• Resistance training prescription
– Children and adolescents: similar to adults
– Emphasis on proper lifting technique
• ACSM, NATA, other guidelines
Table 17.1
Physiological Adaptations
to Exercise Training
• Aerobic training in children
– Little or no change in VO2max
– Performance  due to improved running economy
• Aerobic training in adolescents
– More marked change in VO2max
– Likely due to  heart size, SV
Physiological Adaptations
to Exercise Training
• Anaerobic training in children leads to
–  Resting PCr, ATP, glycogen
–  Phosphofructokinase activity
–  Maximal blood lactate
• Adult anaerobic training programs can be
used with children and adolescents
– Be conservative to reduce risk of overtraining, injury,
loss of interest
– Explore variety of activities and sports
Motor Ability and Sport Performance
• Enhanced motor ability
–  With age until 17 years (boys), puberty (girls)
– Primary factor: neuromuscular and endocrine
changes
– Secondary factor: increased activity
• Why early plateau in girls?
–  Estrogen   fat deposition
–  Fat   performance
– Sedentary lifestyle limits motor ability growth
Figure 17.10a
Figure 17.10b
Figure 17.10c
Figure 17.11a
Figure 17.11b
Figure 17.11c
Figure 17.11d
Special Issues
• Thermal stress
– Children have  surface area:mass ratio
–  Evaporative heat loss ( sweat)
– Slower heat acclimation
– Greater conductive heat loss, gain
• More research needed; be conservative
Special Issues
• Growth with training
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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