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Chapter 5

Introduction to Developmental Psychology - Chapter 5

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Psychology 2410A/B
Sandra Hessels

Physical GrowthThe Course of Physical Growthcompared with other animals primates including humans experience a prolonged period of physical growth physical immaturity is even more exaggerated in humans who devote about 20 percent of their total years to growing this prolonged physical immaturity is adaptive by ensuring that children remain dependent on adults it gives them added time to acquire the knowledge and skills essential for life in a complex social worldChanges in Body Sizethe most obvious signs of physical growth are changes in overall body size during infancy these changes are rapidfaster than at any other time after birth by the end of the first year a typical infants height is 50 percent greater than at birth by 2 years it is 75 percent greater birth weight typically doubles by age 5 months triples by 1 year and quadruples by age 2 growth slows in early and middle childhood when children add about 3 to 8 cm in height and 225 kg in weight eachyear puberty brings a sharp acceleration on average adolescents gain 25 to 28 cm in height and about 22 to 34 kg in weighttwo types of growth curves are used to track overall changes in body size the first is a distance curve which plots the average size of a sample of children at each age indicating typical yearly progress toward maturity during infancy and childhood the two sexes are similar with the typical girl just slightly shorter and lighter than the typical boy around age 10 to 11 the typical North American girl becomes taller and heavier for a time because her pubertal growth spurt takes place two years earlier than the boys at age 14 however she is surpassed by the typical boy whose growth spurt has no started whereas hers is almost finished growth in height is complete for most North American girls by age 16 for boys by age 17 a second type of growth curve the velocity curve which plots the average amount of growth at each yearly interval revealing the exact timing of growth spurtsChanges in Body Proportionsphysical growth during infancy and childhood follows the proximodistal trend from the center of the body outwardduring puberty growth proceeds in the reverse direction the hands legs and feet accelerate first followed by the torso which accounts for most of the adolescent height gainin infancy and childhood girls and boys have similar body proportions during adolescence however large differences appear caused by the action of hormones on the skeletonChanges in MuscleFat Makeupbody fat most of which lies just beneath the skin increases in the last few weeks of parental life and continues to do so after birth reaching a peak at about 9 months of age this early rise in baby fat helps the infant keep a constant body temperature starting in the second year and continuing into middle childhood most toddlers slim down at birth girls have slightly more body fat than boys a difference that persists into the early school years then magnifies around age 8 girls start to add more fat on their arms legs and trunk they continue to do so throughout puberty while the arm and leg fat of adolescent boys decreasesmuscle accumulates slowly throughout infancy and childhood with a dramatic rise at adolescence both sexes again gain muscle at puberty but this increase is 150 percent greater in boys who develop larger skeletal muscles hearts and lung capacity the number of red blood cellsand therefore the ability to carry oxygen from the lungs to the musclesincreases in boys but not in girls altogether boys gain far more muscle strength than girls contributing to their superior athletic performance during the teenage yearsSkeletal Growththe best estimate of a childs physical maturity is skeletal agea measure of development of the bones of the body the embryonic skeleton is first formed out of soft pliable tissue called cartilage in the sixth week of pregnancy cartilage cells begin to harden into bone a gradual process that continues throughout childhood and adolescencejust before birth special growth centres in the bones called epiphyses appear at the extreme ends of each of the bodys long ends cartilage cells continue to be produced at the growth plates of these epiphyses which increase in number throughout childhood and then as growth continues get thinner and disappear after that no further growth in bone length is possible skeletal age can be estimated by Xraying the bones to determine the number of epiphyses and the extent to which they are fusedAfricanAmerican children tend to be slightly ahead of CaucasianAmerican children in skeletal age girls are considerably ahead of boysa gap of about four to six weeks at birth which widens over infancy and childhood girls are advanced in development of other organs as well this greater physical maturity may contribute to girls greater resistance to harmful environmental influencesGains in Gross Motor Skillsas the body becomes more streamlines and less topheavy the center of gravity shifts downward toward the trunk the resulting improvement in balance paves the way for new motor skills involving large muscles Advances in Early and Middle Childhoodby age 2 preschoolers gaits become smooth and rhythmicsecure enough that they soon leave the ground first by running and jumping and then between 3 and 6 years by hopping galloping and skipping Organized Youth Sportstodays schoolage children and adolescents devote less time to outdoor informal physical play than children in previous generations at the same time organized sports have expanded tremendously about half of North American youngsters60 percent of boys and 40 percent of girlsparticipate in organized sports at some time during the school year between ages 6 and 12 For most children playing on the athletic team is associated with increased selfesteem and social competence children who view themselves as good at sports are more likely to continue playing on teams in adolescence whichin turnpredicts greater participation in sports and other physical fitness activities in early adulthood children who join teams before they are capable of the necessary skills soon lose interest coaches and parents who criticize rather than encourage can prompt intense anxiety in some children rather than prompting elite performance high parental pressure to excel at sports and frequent intense practice are linked to childrens emotional difficulties and early athletic dropout Injuries tend to be infrequent and mild except in football which has a high rate of serious injury excessive practice in any sport can lead to painful overuse and to stressrelated fractures resulting in premature closure of the epiphyses of the long bones When parents and coaches emphasize effort improvement and teamwork and permit children to contribute to rules and strategies young athletes enjoy their chosen sport more try harder to improve their skills and perceive themselves as more competent this positive emphasis helps promote physical activity an important factor at a time when less than 30 percent of US and Canadian schoolage children and adolescents engage in enough regular vigorous aerobic activity for good healthHormonal Influences on Physical Growth
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