Kin 315-Ch.8: Physical Growth, Maturation, & Aging

Changes to Individual Constraints are influenced by

A combination of factors:

• Genetic: drive orderly and sequenced pattern of growth and aging

• Extrinsic: examples would be nutrition and disease

Universality

patterns across all humans

Variability

individual differences

Developmentally Appropriate

• motor tasks that are achievable by a given range of ages and abilities

• Educators/therapists should make sure tasks are

Embryonic Development: Timeline

Conception to 8 weeks

• Conception: male and female sex cells fuse together

Embryonic Development: Differentiation of Cells

• 1st stage of embryonic development

• forms tissues and organs

• differentiation: cells become specialized, form specific tissues and organs

  • by the time the embryo implants into the uterus, it is several hundred cells in size

Embryonic Development: 4 Weeks

• 2nd stage of embryonic development

• Limbs formed

Embryonic Development: 8 Weeks

• final stage of embryonic development

• human form noticeable

  • eyes, ears, nose, mouth, fingers, toes

Fetal Development: Timeline

• 8 weeks to birth

• further growth and cell differentiation of the fetus, leading to functional capacity

Fetal Development: Continued Growth via…

• Hyperplasia

  • increase in cell #

• Hypertrophy

  • increase in cell size

Cephalocaudal

• one of the directions of development in fetal development

• head to toe

• head, facial structures —> upper body —> lower body

Proximodistal

• one of the directions of development in fetal development

• near to far

• trunk —> proximal limb parts —> distal limb parts

Plasticity

• part of fetal development

• the capability to take on new function

  • ex: if some cells in a system are damaged, the other cells can work to perform the role of the damaged cells

• cells in the CNS have a high degree of this

Fetal Nourishment

• Placenta: where O2 and nutrients diffuse between fetal and maternal blood

  • place of CO2 and waste products exchange

• Maternal health status affects fetus

  • if in low supply, mother and fetus compete for these resources

• Low birth-weight: infants are at greater risk of disease, infection, and death in the weeks after birth than normal-weight infants

Abnormal Prenatal Development

• Source can be:

  • Genetic: inherited, may be immediately apparent or remain undetected until well into postnatal growth

  • Extrinsic: drugs and chemicals in mother’s bloodstream, viruses, excessive pressure applied to mother’s abdomen

• Types:

  • Congenital (present at birth; due to either genetic or extrinsic factors)

  • Non-congenital

Abnormal Prenatal Development: Genetic Causes

• Dominant disorders: defective gene from one parent

• Recessive disorders: defective gene from each parent

• Gene mutation: could be spontaneous or from irradiation, environmental toxins, etc.

• Mutation of egg or sperm cell (not necessarily inherited)

Abnormal Prenatal Development: Effects on Growth/Maturation

• Variable in appearance and severity

  • malformation of limb, organ

  • deformation of body part

  • mental problems

  • visual impairment

  • body systems dysfunction

• Many are obvious at birth, but some do not appear until later

Abnormal Fetal Development: Example of Genetic Disability

• Down Syndrome (aka Trisomy 21)

  • chromosomal anomaly

  • usually an egg and sperm have 23 chromosomes; after fertilization an embryo ends up with a complete set of 46 chromosomes

  • sometimes an egg or sperm cell keeps both chromosome 21s, so the embryo has an extra chromosome 21

Abnormal Fetal Development: Example of Abnormal Development Due to Extrinsic Factors

• Fetal alcohol syndrome

• occurs when mother consumes alcohol when pregnant

Abnormal Development: External Causes

• Nourishment

• Physical environment

• Teratogen: drug/chemical agent that causes abnormal prenatal development; can be from too much/too little of substance; delivered through nourishment system

  • effects depend on when the fetus was exposed (critical periods) and the amount of substance

  • example: too little folic acid (B vitamin)—needed for spinal development, too little could lead to spina bifida (incomplete neural development)

TLDR: external factors can be diet/medications, environment, and conditions/diseases

Abnormal Fetal Development: Harmful Environmental Factors

Placenta screens some substances (ex: large viruses) but not all harmful things

• Pressure (could also include internal pressure from other fetus in utero)

• Temperature: extreme internal temp (ex: when mother has high fever or hypothermia)

• X Rays

• Gamma Rays

• Atmospheric Pressure (ex: hypoxia aka O2 deficiency)

• Pollutants (environmental such as air pollution and secondhand smoke)

• Other (smoke, alcohol, drugs, raw food, etc.)

Timing is important—ex) Rubella virus is most dangerous if fetus is exposed during the critical period (first four weeks) of pregnancy

Most vulnerable: tissues undergoing rapid development at time of exposure

Postnatal Development: Growth Pattern

Sigmoid (s-shaped: sigmoid is the Greek letter for S)

Postnatal Development: Timing of Spurts vs. Steady Periods

• Generally universal

• Varies among individuals

• Differs between the sexes

  • usually rapid growth (height and weight) after birth (aka during infancy), steady growth during childhood, rapid growth during early adolescence, and a leveling/tapering off

Height (General)

• Sigmoid pattern

  • Although a normal growth curve is always sigmoid, the timing of a particular individual’s spurts and steady growth periods is likely to vary from the average

• Long growth period of males contributes to absolute height differences

Height (Boys)

• Peak Height Velocity: 13.5-14 yr

• Growth:

  • tapers off ~17 yrs

  • ends ~ 18 yrs

• Height Curve for boys 0-20 years old

  • Note the 2 steep slopes first:

    • ~0-1 yr

    • ~12-14 yr

  • This shows:

    • Universality (general shape of the curve)

    • Variability (percentiles)

Height (Girls)

• Peak Height Velocity: 11.5-12 yr

• Growth:

  • tapers off ~14 yrs

  • ends ~ 16 yrs

• Height Curve for girls 0-20 years old

  • Note the 2 steep slopes first:

    • ~0-1 yr

    • ~10-12 yr

  • This shows:

    • Universality (general shape of the curve)

    • Variability (percentiles: aka timing and steepness of segments of the curve are specific to the individual)

Height: Velocity Curves

• After age 2 the rate of growth slows until the adolescent growth spurt. Note the ages at peak height velocity

• Longer period of greater rate of growing for boys = absolute height differences

  • Note: males have about 2 more years of growth than females

  • Boys peak height velocity is somewhat faster than that of girls

    • 9cm/yr vs. 8cm/yr

• Girls begin their adolescent growth spurt when they are about 9, whereas boys begin theirs at about 11 (these are age group averages)

Weight

• Sigmoid pattern

• Susceptible to extrinsic factors (especially in early adulthood)

  • diet

  • exercise

  • disease

• People:

  • grow up (height)

  • fill out (weight)

• Peak weight velocity

  • follows peak height velocity; height velocity peaks occur before or at the same time as weight velocity peaks

  • by 2.5-5 months (boys)

  • by 3.5-10.5 months (girls)

Boys Weight (chart)

Girls Weight (chart)

Postnatal Growth: Extent vs. Rate

• Distance curves = extent of growth

• Velocity curves = rate of growth

• Peaks on velocity curves show ages that growth rate changes

Postnatal Growth: Relative Growth

• Body overall: sigmoid pattern

• Specific parts/tissues/organs: differential growth rates

• For example, the brain achieves more than 80% of its adult weight by age 4. So, even if 5-months old infants were neurologically ready to coordinate and control the walking pattern, it is unlikely they could balance their top-heavy bodies on such thin, short legs and small feet. This is a reminder that changing individual structural constraints related to body form and proportion could certainly interact with task and environment to produce different movements

Postnatal Growth: Body Proportions

• Changes from head-heavy, short-legged form at birth to adult proportions

• Adolescent boys: increase shoulder breadth

• Adolescent girls: increase shoulder and hip breadth

Physiological Maturation

Size and Maturation

• Physiological maturation: the developmental process leading to a state of full function

  • increase in children/youth with age

  • rate varies

• Can measure maturation:

  • Indirectly: compare anthropometric measurements

  • Directly: qualitative assessment of secondary sex characteristics, measure skeletal maturation

• Secondary Sex Characteristics

  • appear as a function of maturation (based on hormone changes)

  • appear at younger age in early maturers

  • girls (as a group) mature sooner and at a faster rate than boys

  • Primary sex characteristics: appear at birth

How should we counsel parents of an early maturer and star athlete about the child’s future in athletics?

Maturation status is relevant as a structured constraint influencing movement.

It is tempting to infer movement performance potential from size and/or age, but maturation status is a powerful predictor of performance potential.

How concerned should we be if a young teen seems more awkward than he/she was in childhood?

Periods of motor incoordination, or “adolescence awkwardness,” may occur during the adolescent growth spurt. These are temporary and not associated with any underlying dysfunction. They may be associated with an increased risk of injury.

Postnatal Growth: Extrinsic Influences

• especially sensitive during rapid growth periods

  • Genetics control the timing and rate of growth and maturation, but extrinsic factors (especially those influencing metabolism) can have a great effect.

  • For example, not having enough food for nourishment (severe malnutrition) can slow growth. Could also be due to severe disorder.

• Catch-up growth (CG): period of rapid growth to recover some or all potential growth lost during period of negative extrinsic influence. Occurs once negative influence is removed.

  • Whether a child recovers some or all of the growth depends on the timing, duration, and severity of the negative environmental condition.

Adulthood and Aging: Height

• Growth ends for humans in the late teens or early 20s

• Stable in adulthood

• May decrease in older age

  • compression of cartilage pads, mainly in the spine

  • osteoporosis: decreased bone density that can lead to decreased height due to compression fractures of the vertebrae (which can lead to kyphosis aka “dowager’s hump”) and increased pressure in the abdominal cavity

Adulthood and Aging: Weight

• Increases starting in 20s

  • diet

  • hormones

  • exercise (sedentary)

  • decreased muscle mass

    • inactivity

    • appetite (unhealthy/lack of)

  • Active adults are not as likely to lose muscle mass