Week 2: Lecture 4 - Physical Growth

Physical Growth

Growth begins in a general cephalocaudal and proximodistal pattern

Cephalocaudal

Growth first occurs in the head and gradually proceeds downward to the neck, shoulders, and trunk

Proximodistal

Growth proceeds from the center of the body and

moves toward the extremities

Physical Growth across the Lifespan - Gestation and the 1st year after birth

Individuals grow at a faster rate than they will at any other time in their lives

Physical Growth across the Lifespan - Early Childhood years

Growth progresses at a relatively uniform and steady rate

Physical Growth across the Lifespan - Middle & late Childhood years

Growth is a relatively slow, consistent proces

Physical Growth across the Lifespan - Early adolescence

• Onset of puberty

• Dramatic biological change

• Pubescent growth spurt represents a landmark in physical growth with regard to sex differences and motor performance

Physical Growth across the Lifespan - Early adulthood

Physical development usually begins to slow down

Physical Growth across the Lifespan - Aging

As people age, they generally get shorter, lose muscle mass, experience a change in body proportions, and get heavie

Physical Growth across the Lifespan - Older adulthood

Individuals tend to become lighter than they were during middle adulthood due in large part to losses in bone and muscle mass

Anthropometry

Branch of science concerned with biological growth and body measurement

Prenatal period

- plays a significant role in human development

- Events that take place during this period forge the foundation for future development across the life span

- In comparison to the other developmental stages of life, the prenatal period presents the greatest variation in human growth and development

Prenatal: Conception

Sperm unites with ovum (zygote) in Fallopian tube and

begins its journey to the uterus

What is the time range for the germinal period?

- Lasts for approximately 14 days after conception

What happens almost immediately in the germinal period?

- Almost immediately, the 23 chromosomes from the sperm cell nucleus combine with the 23 chromosomes from the ovum to produce 46 chromosomes

What is the Prenatal: Germinal period (1st 2 weeks)

- The chromosomes then uncoil and split, yielding 46 strands of deoxyribonucleic acid, which serve as the template in the development of the individual

- Rapid cell division

- Implantation

What is the embryonic time range?

- Lasts from about 2 to 8 weeks after conception

what is the Prenatal: Embryonic period (2-8 weeks)

- By 2 weeks after conception, the distinct layers of cells is called an embryo

- Human form begins to take shape

- Some of the finer features such as the eyes, ears, fingers, and toes are also discernible

After 8 weeks how big is the fetus?

- After 8 weeks, it is 1 inch long and weighs only 14 g

- The basic parts of the body—the head, trunk, arms, and legs—can be identified

What is relatively developed in the embryonic period?

- The central nervous system (CNS) is relatively developed, and the internal organs (e.g., the heart, lungs, reproductive organs, liver, and kidneys) are beginning to function to some degree

Skeletal Growth

Begins with the formation of mesoderm cells in the embryo about 16 days after fertilization

Skeletal Growth - 5 to 6 weeks after conception

- Ossification centers appear in the jawbones and collarbones

- Long bones of the upper arm and leg appear in a cartilage for

Skeletal Growth - 2 Months

- Cartilage takes the shape of a long bone

- A ring of true bone begins to form

Skeletal Growth - 3 Months

- Primary ossification centers begin to appear in the midportion

(diaphysis) of the long bones

Prenatal: Fetal period (8 weeks - birth)

- Flexible cartilage is replaced by bone in a process called ossification

- First muscle movements in the mouth and jaw

Prenatal: Fetal period 8th week

- Begins about the 8th week, when the embryo becomes a recognizable human being, and lasts until the time of birth

Prenatal: Fetal period 9th week

- By the 9th week, the muscles of the arms and legs are capable of responding to tactile stimulation

Prenatal: Fetal period (months 4)

- The 4th month of fetal development is a period of significant growth

- The fetus will increase in length to about 6 inches (15 cm) and in weight to approximately 4 ounces (113 g)

- Although a considerable amount of growth has already

occurred in the upper body, there is now a growth spurt of the lower parts of the body in the cephalocaudal direction

Prenatal: Fetal period (months 5)

- By the end of the 5th month, the fetus is approximately 12 inches (30 cm) in length and weighs about 1 pound (454 g)

Prenatal: Fetal period (months 6)

- During the 6th month, the fetus weighs approximately 2 pounds (907 g) and is about 14 inches (36 cm) long

Prenatal: Fetal period (month 7)

- The 7th month is sometimes called the age of viability, i.e., the fetus has matured enough to have a good chance of surviving outside of the womb if birth comes prematurely

- Although not a certainty for all, due to medical advances in neonatal care, many babies survive born at 25 weeks with body weights of less than 3 pounds (1,361 g)

- The internal organs are functioning, and the brain can now regulate breathing, body temperature, and swallowing

- The fetus is about 16 inches (41 cm) long and weighs close to 3 pounds (1,361 g)

When can muscle fibres be identified?

- Muscle fibers can be identified after the 16th week of fetal development

What is voluntary muscle growth like in the prenatal period and after birht?

- Growth of voluntary muscle during the prenatal period is both hyperplastic and hypertrophic

- The hyperplastic phase continues until shortly after birth, after which cell growth is predominantly achieved by increasing cell size hypertrophy

What is the increased mass of skeletal muscle due to?

- The increase in mass of a skeletal muscle of up to 50 times during postnatal development is due almost exclusively to a massive increase in the size of individual fibers

What is the importance of protein?

- Protein, the essential element in muscle composition, increases gradually during the fetal period and, by birth, reaches a level very near that found in adult

Prenatal: Fetal period and weight gain (months 8 & 9)

- The 8th & 9th months are a period of rapid weight gain

The fetus gains about half a pound per week for a total of 5 pounds (2,268 g) for the 2-month period, on the average

- Just a few weeks prior to birth (and at delivery), the average fetus is 20 inches (51 cm) long and weighs about 7 pounds (3.2 kg)

- During these months, fatty layers are developing that will help to nourish the fetus after birth

Physical Growth from Birth to Adulthood

- Head size will double

- Trunk length will triple

- The length of the upper limbs will quadruple

- Length of the lower limbs will quintuple (legs grow at a faster rate than other body parts)

Body Proportion - Newborn

Head = ¼ total height

Legs = ⅜ total height

Head width = that of the

shoulders and hips

Body Proportion - Adult

Head = ⅛ total height

Legs = ½ total height

Head width = ⅓ of

shoulder width

Shoulder width > hip width

When is the fastest growth period for height?

• Growth rates that occur during the 9 months preceding birth

and the 1st year of life are the fastest the body will experience

• Increase in birth length by 50% at 1 year

After the age of 2, what happens with growth?

• After age 2, the growth rate slows to average about 2 inches per year until the onset of the pubescent growth spurt

What is puberty like in regard to height for males and females?

• Until puberty, males on average are slightly taller than females; however, there is a large overlap, with some females taller than males

• Females generally enter the height growth spurt 2 years earlier than males and complete the process in a shorter period of time

Growth accelerates before and during puberty, with peak rates of?

• Growth accelerates before and during puberty, with peak rates of between 3 and 4 inches per year

Physical Growth in Childhood - Mass

- At birth the average fetus weighs about 7 lb (3.2 kg)

- Females are about ½ lb smaller than males

- Body weight typically doubles after 3 to 4 months and triples at 1 year

- Many children will reach ½ of their mature body mass by age 10 years

Pubescent growth spurt for body weight is similar to

the height curve, except that it generally continues for a longer time

At what age is female rapid growth?

Female growth patterns reveal a particularly rapid weight gain between the ages of 12 and 13 years

When do males begin their growth spurt?

As in the growth pattern for height, males begin the growth spurt later than females do and add more body size

Mature body weight is???

about 20 times that of birth weight

What is total body mass decline a reflection of?

Total body mass begins to decline with aging as a reflection of bone and muscle tissue losses

Pubescent Growth Spurt

Lifespan's most dramatic period of biological change

- Begins at about 10 to 13 years of age in females and 12 to 15 years of age in males

-Wide range of ages at which individuals enter puberty

- Variation in individual differences

How long does the puberty growth spurt last?

- Lasts for 2 to 3 years

What is the growth spurt period like for females?

-Go through the pubertal period in a shorter time than males

-Typically about 2 years ahead of males in maturity

Puberty

• Rapid changes in physical maturation and growth

• Occurs during early adolescence

• Controlled primarily by genetic factors and hormones

• ⅔ of the variation in age of puberty is genetic

• Sexual maturation

• Stage of maturation in which the individual becomes

physiologically capable of sexual reproduction

Pubescent Growth Spurt - beginning of sexual maturity (female)

- Breasts and pubic hair first appear

- This period of development is highlighted by a universal maturity landmark known as menarche, or the time of the female's first menstrual flow

- The average age at menarche is about 12.5 years

- May occur as early as the age of 10 years or as late as 15.5 years

- A major influence on the onset of puberty in females is body fat

- girls with more body fat tend to reach menarche earlier than girls of average and below-average body fat

Pubescent Growth Spurt - beginning of sexual maturity (male)

- Appearance of pubic and facial hair

- Change in voice

- Increase in the size of the reproductive organs

What is menarche?

• Mean age of menarche has been declining an average of about 4 months per decade

• Due primarily to improved health conditions and nutrition, females are maturing earlier

What is thelarche?

• The age of thelarche (onset of breast development) decreased by 3 months per decade from 1977 to 2013

Hormonal Influences

• Pituitary gland

• Master gland

• Regulates the endocrine system

• Produces growth hormone (GH), one of

The primary agents that stimulate the

adolescent growth spurt

• Hypothalamus

• Gonads (sex glands)

• Thyroid gland

• Adrenal glands

Hormonal Influences - 01

Puberty begins as increased levels of hormones enter the bloodstream in response to signals from the hypothalamus

Hormonal Influences - 02

These signals instruct the pituitary to release GH and stimulate production of thyroxine (from the thyroid) and sex hormones (from the gonads)

Hormonal Influences - 03

Together, GH and thyroxine contribute strongly to the tremendous gain in body size and the completion of skeletal maturation during puberty

Physical Growth - most important hormonal influence

- The interaction between GH and androgens produced by the gonads is significant

- After a signal from the hypothalamus, the pituitary sends a signal via gonadotropins to stimulate the production of estrogen in the ovaries (female) and androgens (mostly testosterone) in the testes (male)

- When secretions of these hormones reach critical levels, the pituitary produces more GH, resulting in the growth spurt in both sexes

Throughout childhood, the male and female bodies produce approximate levels of.......

estrogens and androgens

Androgens

play a significant role in hastening the fusion of epiphyseal growth plates in the bones and stimulating the protein synthesis required for the development of muscle tissue

Are estrogen and testosterone present in both sexes?

Both hormones are present in both sexes, but testosterone dominates in males

- Adolescent boys experience larger growth spurts than girls

Testosterone in boys and girls

levels increase 10-fold in boys but only 2-fold in girls

What is estrogen?

- Estrogen, although important to the growth spurt and bone development in females, promotes the accumulation of body fat

How does estrogen impact females?

• Although females may continue to develop muscle tissue (due to the presence of GH and androgens), the effects of estrogen may account for the greater amount of fatty tissue in comparison to males

• Estrogens cause a quicker closure of the epiphyseal (bone) plate than testosterone

• Females usually do not reach the same height as males

Estrogen increase in boys and girls??

levels increase 10-fold in girls but only 2-fold in boys

Growth Plate Closure

- Epiphyseal plate closure is indicative of long bone maturity

- Starts between 13.5 and 18 years of age

- Begins at the distal humerus

When do long bones reach maturity?

- Most of the long bones reach maturity from about 16 to 18 years of age in females and 18 to 21 years in males

What happens when full maturity is reached for long bones?

- When full maturity is completed, the epiphysis fuses to the metaphysis (the area between diaphysis and epiphysis), and the growth plate is erased

Appositional Growth - Bone Girth

- New rings of bone are added in circular layers on top of the layers formed earlier

- The bone has a compensating mechanism that controls thickness

- As new rings are added, old layers are removed from the inner circumference of the bone sleeve, permitting the shell to become thicker

When does the process of appositional growth occur?

- This process continues until each of the long bones reaches full maturity in late childhood to early adulthood

When is the maximum growth of the long bone reached?

• Maximum growth of the long bones may not be reached until age 25 years and of the vertebral column until 30 years, at which time an individual may add ⅛ - ¼ inch

• Height remains relatively stable until sometime after the 3rd decade of life, when total height begins to regress

When do females and males complete their peak growth?

• Females complete their peak growth period by 16.5 years of age

• Males continue to gain in stature for another 2 years or so

• Males are typically 4 to 6 inches taller than females when they reach mature height

The Skeleton in Adulthood

- Normal aging causes the bones to lose mass and the total height to decrease

When do women begin to lose bone mineral?

- Women begin to lose bone mineral at about age 30 and men at 50

- Bone loss in women begins slowly during the 3rd

decade (0.75% to 1% per year)

- Can increase to a higher rate (2% to 3% per year) shortly before and after menopause

- Total bone mineral mass loss by age 70 is approximately 25% to 30%

- Bone loss estimates for men at age 70 are about ½ of what women experience

- The amount of bone loss is specific to the individual and varies considerably in different types of bon

The Skeleton in Adulthood - Age

• Stature decreases with age

• Increase in postural kyphosis (rounding

of the back)

• Compression of intravertebral disks

• Deterioration of vertebrae

• Estimates of height decreases from 40 to 80 years of age are 1 to 3 inches

What is osteoporosis?

- Loss of total bone mass to such an extent that the skeleton is unable to maintain its mechanical integrity

- Bones tend to break more easily, which increases the risk of fracture

What is Osteoporosis influenced by?

- Influenced by a variety of nutritional (related

primarily to calcium), physical, hormonal (primarily estrogen), and genetic factors

Who is most affected by osteoporosis?

- Almost ½ of all women older than the age of 60 years are affected by osteoporosis

What makes up 15% of a fetus's body mass?

- Approximately 15% of total body mass of the fetus halfway through its development consists of skeletal muscle tissue

- This percentage increases progressively to about 25% of

birth weight for both sexes

How much mass does an adult skeleton take up?

- Approximately 40% to 50% of body mass in the adult male are skeletal muscle

What does lean body mass mean for females?

- Females generally do not show a significant increase in lean body mass during puberty and at maturity, they have about 60% of the muscle mass and force characteristics of males

With aging, there are changes in what mass?

- Significant changes in body fat and lean muscle mass take place with aging

When does weight start to decline?

- Although height decreases with age, weight increases steadily beginning in the 3rd decade and continues until 55 to 60 years of age when it declines

- An increase in body weight is usually accompanied by gains in body fat and a decrease in lean body mass

Physical Growth in Adulthood - Mass

- By the end of adolescence, the average male is 23% fat and by 60 years increases to about 31%

- Females change from about 32% body fat at 17 years to approximately 42% at 60 years

- These values can vary to quite an extent depending on lifestyle and tend to be less in individuals who are physically active

- After age 60 years or so, total body weight decreases despite the increase in body fat due in part to loss of muscle and bone mas

Infants who are longer for their weight tend to walk at an earlier age

• Initial walking patterns of the early group are quite immature

• Delayed groups usually catch up quickly

Inverse relationship between excess body fat and performance on a variety

of tasks

• Boys and girls (age 9 to 16 years) who were not overweight were 2 to 3 times more likely to possess advanced locomotor skills than those who were overweight

• In tasks requiring that an object be propelled or force be applied, increasing body size (fat-free mass) usually has a positive effect on performance

Center of gravity remains constant, what does not?

- Although the center of gravity remains relatively constant in proportion to total height with age, the center of gravity is higher in children because they carry a greater proportion of weight in the upper body

Females have a lower centre of gravity

- Females have a lower center of gravity than males, which in combination with their shorter legs, contributes to the better performance of females in tasks requiring balance.

Why are females at a disadvantage in running?

Shorter leg length and wider hips, however, are disadvantageous in running (especially sprinting) and jumping events when compared to the performance of males whose legs are proportionately longer and whose hips are narrower

What provides males with a mechanical advantage?

- The male's longer arms and wider shoulders also may provide a mechanical advantage for motor tasks involving throwing and striking