Children and Adolescents in Sport and Exercise Chapter 17 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 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 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 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

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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 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 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

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 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 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

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Figure 17.10c

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Special Issues Thermal stress More research needed; be conservative 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 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