Muscular System• Muscle fibers (cells) grow during prenatal period• Birth muscle mass is 25% of body weight• Gender differences are minimal in children• Males 54% of body weight, females 45% of body

weight• Type I: slow twitch (endurance)• Type II: fast twitch (anaerobic)• At birth 20% of muscle cells are undifferentiated• Early activities may affect proportion but fixed by

age 1

Motor Units• All muscle fibers are attached to by a nerve

(innervated) which is a motor unit• Fast or slow twitch (depending on speed of

contraction and relaxation)• Older Adults

– Compared to young adults: % of muscle decreases (training can alter effects)

– Old age: number and size of fibers decreases– Muscle mass is influenced by: genetic inheritance,

insulin level, growth hormone level, nutrition, activity and training level

Cardiac Muscle

• The heart is made up of muscle tissue and goes through same growth process as the rest of the body

• Left ventricle starts off smaller but catches up

• Has same growth pattern as body

Adipose System• Plays a vital role in energy storage, insulation, and

protection • Appears at 3.5 months and increases rapidly the

final 2 months of pregnancy• Fat mass increases until age 8• Girls experience more dramatic increase during

adolescence• After 8, fat levels are generally maintained• Adipose increases most in first 6 postnatal months

and puberty• Older Adults

– Both genders increase, body weight decreases after 50

Endocrine System• Hormones play important role in regulating

growth and maturation• Interaction of hormones, genes, nutrients and

environment• Interact together in feedback loops and work

together to regulate the levels of hormones in the body

• 3 types1. Pituitary growth hormone2. Thyroid hormones 3. Two gonadal hormones

Hormones

• Excess or deficiency will alter process• Stimulate protein anabolism• Results in retention of substances needed to build

tissue• Growth hormone

– Important during childhood and adolescence– Under control of CNS– Secreted by anterior pituitary gland– Enhances mobilization of stored fat and conserves

carbohydrates

• Thyroid Hormones– Thyroid gland is in anterior neck region– Increases the oxygen consumption in the tissues– Decreases circulating calcium, promotes calcium

deposition in bones

• Gonadal Hormones– Most active during adolescence– Stimulate the development of secondary sex

characteristics and sex organs– Androgens hasten the fusion of the growth plates – Increase muscle mass– Women have more estrogens which speed up growth

plate closure and increase fat accumulation– Genders have both types but in very different quantities

• Insulin– Indirect role in growth – Produced in pancreas– Vital to carbohydrate metabolism and necessary for full

function of growth hormone

• Older Adults– Regulation of cardiovascular performance– Mobilization of fuel– Synthesis of new protein– Base levels of GH are stable– Exercise causes larger increase in GH levels than in

younger people– Thyroid function decreases– Decreased levels of gonadal hormones– Don’t utilize insulin as effectively

Nervous System• Early development genetically determined• Cell growth occurs early but cells mature

postnatally• Many nervous cells have tremendous plasticity• Brain

– Develops rapidly– Increase in myelin and glial cells– Increase in size of neurons and arborization– Connections established with other neurons in 1st yr– Form synapses with each other; increases firing which

is crucial for brain development

• Lower brain centers– Respiration, food intake, reflexes, reactions

– Automatic movements dominate fetus and newborn movements

– Onset of goal directed movement: sign of higher brain function

– Most mature at birth

• Myelin– Insulation around nerve cell

– Interrupted by nodes of Ranvier

– Impulse jumps from node to node

– Unmyelinated cells slower and fire less frequently

Spinal Cord

• Small and short at birth• Myelinization 2-3 weeks after birth• 2 motor pathways

1. Extrapyramidal tract (reactions)2. Pyramidal tract (intentional)

• Older Adults– Decreased number of neurons– Decreased brain weight– Decreased signal strength and number of neural

connections

Factors Affecting Postnatal Dev.

• Important to recognize environmental influences• May affect “critical periods” of learning• Birth process• Traumatic for fetus• Umbilical cord important for oxygen• Low birth weight is indicative of greater health

risks• If improve environment, catch up growth may

occur

Postnatal Nutrition

• Body needs energy that food provides to grow and maintain body functions

• Important for maintenance and repair of tissues through life

• Proteins, carbohydrates, and fat are all important– Proteins: amino acids and building material for various

tissues– Carbohydrates: chief source of fuel and energy– Fats: energy storage and insulation from heat loss– Also contributing are water, vitamins, and minerals

Nutrition• Malnutrition

– Decrease in stature and may not attain potential height, delay puberty

– Can decrease CNS function– Occurs everywhere, not just underdeveloped nations– May be caused by heavy physical training

• Overnutrition– Due to too much sugar and fat and not enough activity – Most prevalent in affluent areas– Obesity increases growth and development but also

cholesterol and tryglicerides

Physical Environment• Climate

– Tall, and thin are more common in hot climates– Short and stocky are more common in cold climates

• Seasons– Greater weight gains in fall than spring– Greater height gains in spring than fall– May be due to nutrition and exercise patterns

• Altitude– High altitude leads to smaller bodies and growth rates

• Other– Radiation: cell mutations, damage to NS– Lead poisoning: decreased neurological growth

Physical Activity and Training

• Everyone needs some minimum to support growth • Must keep in mind level of training and emphasis• Skeletal growth

– Physical activity doesn’t affect length– Evidence that it increases diameter and density

• Body weight– Increases lean body mass and decreases fat weight

• Body physique and maturation– Doesn’t affect much

Capacity for Exercise

• Decreases with age

• Stronger skeletons, stronger muscles, increased endurance, flexibility, decreased fat weight, faster reaction times, increased brain function

• If excessive, may lead to injury