Week 3 Pt1

Introduction to Biomedical Physiology and Kinesiology - Growth and Development

• Growth is the progressive development of a living being or part of an organism from its earliest stage to maturity, including increases in size.
• Monitoring growth and development can identify problems in those who are not developing typically.
• Studying growth helps create developmentally appropriate movement curricula and programming.
• Growth is more than adding material; it involves differentiation of body parts for specific functions.
• Not all parts of the human body grow at the same rate, nor do they all stop growing simultaneously.
• Body proportions and relative weights of tissues/organs change throughout growth.
• The brain at birth is 24% of adult weight, while the neonatal body is 6% of adult weight.
• Extremely rapid brain growth continues, reaching 90% of adult weight by 5 years old, but body weight is only 25% of adult weight by that age.
• Reproductive organs remain at less than 10% of their final weight until puberty.
• The five stages of postnatal growth are: neonatal period, infancy, childhood, adolescence, and adulthood.

Stages of Postnatal Growth

• Neonatal period (birth to 4 weeks): first four weeks.
• Infancy (4 weeks to 2 years): characterized by tremendous growth, increased coordination, and mental development.
• Childhood (2 years to adolescence): growth and development extending from infancy to adolescence; a period of steady growth until preadolescence when a growth spurt occurs. The chronological duration varies due to differences in puberty onset.
• Adolescence (9-11 years to 17-18 years): growth and development period involving growth from childhood to adulthood. Boys typically start around age 11, and girls around 9. The end is roughly around age 17-18, although it's not clearly defined.
• Adulthood: period beyond adolescence wherein maximum physical stature is reached, determined by factors such as genetics, nutrition, and environmental influences.

Growth in Height and Weight

• Growth Curves:

  • Distance curve: Measures height vs. time, plotting measurements over intervals to show growth progress.
  • Velocity curve: Measures change in height/year vs. time or growth increments over time to show variation in growth rate.
  • Data collection methods:
    • Longitudinal: Repeated measurements on the same group or individual over a long period.
    • Cross-sectional: Measurements of several children in each age group combined to show community picture at the time of investigation.

• Growth in Height:

  • Girls reach 50% of adult height at a generally earlier age (1.75 vs. 2.0 years), enter puberty earlier, and cease growing earlier than boys.
  • Before the adolescent growth spurt, little height difference exists between boys and girls.
  • The mean growth takeoff age (onset of acceleration) in North America is generally 9 ± 1 years for girls and 11 ± 1.5 years for boys
  • Girls tend to gain ~16 cm and boys around 20 cm during the growth spurt.
  • Maximum growth velocity occurs in boys around 13.5 years and in girls around 11.5 years.
  • Boys are usually taller than girls because they have two more years of growth before their growth spurt.

• Growth in Weight:

  • Ovum weight (0.005 milligrams) to birth: 3 x 10⁹ fold increase.
  • Birth weight (approx 7.5 lbs) to maturity (20 years) shows a 20 fold increase.
  • Birth to age 2: 4 fold increase; after which, a steady increase of 2-3 kg/year continues until the growth spurt.
  • The peak velocity in weight gain lags behind the height gain by about 3 months.

Bone Mineral Content & Osteoporosis

• Osteoporosis is a condition marked by decreased mineral content in bones, making them brittle and susceptible to fracture.
• Peak bone mineral velocity occurs approximately one year after peak height velocity, suggesting a potentially relevant transient period of bone weakness.
• Adolescent skeletal maturation has a correlation with fracture risk potentially due to the time delay from peak height velocity. Adequate calcium and vitamin D intake are important for healthy bone development.

Changes in Body Proportions & Composition

• Body proportions are not consistent; they change with age.
• Infant's head is proportionally larger (head height:total height = 1:4), while legs are less developed than arms (leg length:total height = 1:3).
• Infant proportions change gradually through growth with peripheral limbs developing before central parts (foot-->calf-->thigh).
• During the adolescent spurt, growth tends to be lateral rather than linear.
• Facial bones grow faster than the cranium.

Puberty

• Puberty is the period where the reproductive organs and secondary sex characteristics rapidly develop, including an enlargement of the testes, prostate gland, seminal vesicles (in males), or breasts, uterus, and vagina (in females).
• Puberty signifies the most striking sexual differentiation.
• Menarche, the onset of menstruation, occurs relatively late in puberty, with an average age around 12.2-13 years in North America, and a standard deviation of one year from this average.
• Height velocity declines around the time of menarche.
• The development of mature ova occurs around the same time as menarche.
• Puberty is not complete until sexual maturity has been attained in females.

Indices of Maturity

• Chronological age is not a good measure of maturity.
• Different maturity indicators (radiological, dental, growth curves, sexual, neural) may not correlate.

Skeletal Age

• Radiographic recordings of bone development, such as in the wrist and hand, can precisely identify maturity stages.
• Radiological age usually precedes chronological age, especially in girls, by approximately 20%.

Dental Age

• Deciduous (baby) teeth erupt from age 6 months to two years; can serve as temporary maturity markers.
• Permanent teeth are used to assess maturity from age 6 to 13 years.
• Skeletal and dental ages are often not strongly related.

Growth Curve

• Timing of peak height and weight velocity serve as indicators of maturity development.

Sexual Age

• Stages of pubic hair, breast, and genital development are used to rate maturational development.
• Tanner stages classify development.

Early/Late Maturing Children

• Five types of skeletal development identified: average, early tall, early genetically tall, late small, late genetically short.
• Early maturation can correlate positively with higher scores on mental ability tests relative to less mature peers.

Factors influencing Growth and Maturation

• Genetic control: Studies showing similarities in body shape and growth patterns among twins imply an important role of heredity.
• Nutrition: Malnutrition delays growth, and even relatively mild malnutrition affects proportions.
• Secular trends: Average height in North Americans and Western Europeans has increased over time (1.0cm per decade).
• Season/climate: Height growth appears to be greater in spring and summer. Weight gain appears to be greater during autumn.
• **Race:**Slight differences in average growth and development rates exist among different racial groups.