Endocrine Responses to Resistance Exercise

Endocrine System• One of eleven major body organ systems• Composed of a system of glands that secrete

hormones • A hormone is a chemical messenger that is

synthesized, stored, and released into the blood by endocrine glands and certain other cells– Works with the nervous system in controlling the

growth and maturation of the body along with the daily activity of internal organs

– Works to coordinate the body’s long-range response to external stimuli

– Tissue and muscle growth

Endocrine System

• It has been theorized that the endocrine system can be manipulated naturally with resistance training to enhance the development of various target tissues, thereby improving performance.

Endocrine Glands That Release Hormones

• Pituitary • Hypothalamus • Pineal • Thyroid • Parathyroid • Heart• Liver• Adrenal • Kidneys• Pancreas • Testes • Ovaries

Pituitary Gland• Located in the brain

• About the size of a pea with

two lobes

• Regulates the activities of

other endocrine glands

in the body

• Secretes Growth Hormone (GH)

Pineal Gland• Located in the center of the brain

• Receives information from the eyes

• Secretes Melatonin

• Melatonin regulates the following:

–Sleep-wake cycles-if the levels are too low then people may have difficulty falling asleep

–Regulates stress

Hypothalamus• Located in the brain above the pituitary gland• Regulates the following:

– Blood pressure– Heart rate– Body temperature– Fluid and electrolyte balance– Thirst and hunger– Mood

• Secretes Dopamine:– Controls voluntary movement

Adrenal Glands and Pancreas• Adrenal Glands:

–A pair of small glands located above each kidney

–Secretes Cortisol and Catecholamines

• Pancreas:

–Located below the stomach and is connected to the small intestine

–Secretes Insulin-stimulates cells to use glucose

Ovaries and Testes• Ovaries secrete the following:

–Estradiol-development of breasts, reproductive organs and secondary female characteristics

–Progesterone-pregnancy –Testosterone-tissue growth

• Testes secrete the following:–Testosterone–Estradiol

.

Mechanism of Hormone Action• Glands release hormones that trigger actions in

specific target cells

• Receptors on target cell membranes bind only to one type of hormone, which changes the shape of the receptor causing the response to the hormone.

–Lock and Key

Lock and Key• Receptor is the lock and the hormone is the

key.• Once the key opens the lock, a message is

sent to the cell to perform a specific action• The genetic material in the nucleus of the cell

translates the message (i.e. protein synthesis or protein breakdown)

Hormones in the Blood• Just because there is a hormone present in the

blood does not mean that it will reach its receptor site

• A higher concentration of hormones in the blood could mean a greater chance of the hormone reaching its receptor site

• Down Regulation: The cell’s receptor is non-responsive to the hormone.

• For a hormone to work:–Adequate blood levels of hormone–Specific binding of hormone to receptor–Transport of hormone via binding

protein

Hormones in the Blood• Interactions with receptors are greater

when– Exercise acutely increases the blood

concentrations of hormones.

• Receptors are less sensitive when– The physiological function to be affected is

already close to a genetic maximum,

– Resting hormone levels are chronically elevated due to disease or drug use

– Mistakes are made in exercise prescriptions

Hormones in the Blood• Activated to help with recovery and adaptation to

stress (resistance training)

• Elicit different responses based on the type and duration of exercise

– If exercise stress is too great or too long in duration, catabolic hormones take over the muscle

• Muscles are a primary target for hormonal interactions

– Muscle remodeling, including repairing damaged fibers, controlling the inflammatory response and the synthesis of new proteins is all caused by hormonal interactions

Classes of Hormones• There are two main categories of hormones:

– Polypeptide (Non-Steroidal)

• Growth Hormone

• Insulin

• Insulin-Like Growth Factor

• Catacholamines

– Steroidal Hormones

• Testosterone

• Estradiol

• Cortisol

Polypeptide Hormones (Non-Steroidal)• Most hormones are peptides• Short chains of amino acids• Water soluble • Secreted by the pituitary gland,

parathyroid gland, heart, stomach, liver, and kidneys

• Do not enter the cell but bind to plasma membrane receptors, generating a chemical signal (second messenger) inside the target cell.

Steroidal Hormones

• Lipids derived from cholesterol

• Fat soluble

• Secreted by the ovaries, testes, and adrenal glands

• Pass through the plasma membrane into cell

Anabolic Hormones • There are four primary

hormones involved in muscle tissue growth and remodeling:

–Testosterone–Growth Hormone–Insulin–Insulin-Like Growth Factor

Testosterone • Steroidal hormone secreted from

the testes in males and ovaries and adrenal glands in females

– Males produce 10 times more than females

• Primary hormone that interacts with skeletal muscle tissue

Testosterone • Both direct and indirect effects on

muscle tissue growth

– Direct

• Following secretion, testosterone is transported to target tissues in the muscle cells. It then migrates to the cell’s nucleus where it causes an increase in protein synthesis.

Testosterone• Indirect

–Promotes growth hormone responses in the pituitary gland

–Causes Insulin-like Growth Factors (IGF) to be released from the liver causing protein synthesis.

–Influences the central nervous system by increasing the amount of neurotransmitters and neuromuscular junctions which enhance muscle size.

Testosterone • May have a role in nervous system development

in long-term training• Increases in concentrations may enhance the

neural adaptations that occur for strength gain in highly trained strength and power athletes

• Diurnal (day) Variations– Men: Exercise later in the day is more effective

for increasing overall testosterone concentrations over an entire day.

– Women: There are lower concentrations and little variation during the day.

Exercise Variables that Increase Testosterone

• Workouts lasting under 60 minutes• Multiple sets of multi-joint exercises • Short rest intervals (< minute)• Heavy resistance (85-95% of 1 RM)• Two or more years of regular RT• High intensity aerobic training causes a

catabolic response• Large muscle group exercises result in

acute increased serum total testosterone concentrations in men.

Growth Hormone (GH) • Secreted by the pituitary

gland • Important for the normal

development of a child• There can be

developmental problems if there is a deficiency or over secretion

• In terms of resistance training, GH plays vital roles in adapting to the stresses that can occur to the body

Growth Hormone • Interacts directly with

target tissues, which include bone, immune cells, skeletal muscle, fat cells, and liver tissue

• Release altered by age, gender, sleep, nutrition, alcohol consumption, and exercise

Growth Hormone • Decreases glucose utilization• Decreases glycogen synthesis• Increases availability of glucose and

amino acids• Increases amino acid transport across cell

membranes• Increases protein synthesis• Increases lipolysis (fat breakdown)

• Increases collagen synthesis

• Stimulates cartilage growth

Growth Hormone • Enhances amino acid uptake and protein synthesis in

skeletal muscle– What that means is that it will result in hypertrophy

in our Type 1 and Type 2 muscle fibers• Responds to exercise stressors, including resistance

exercise. • Response depends on load, rest, and volume of

exercise.• Responses in Women:

– Concentrations and responses to exercise vary with menstrual phase

– Women have higher blood levels of GH than do men.

Growth Hormone • To increase your levels, you can use

either or both of these combinations:–Workouts with higher lactate-

concentrations and associated acid-base disruptions (i.e., high intensity, 10 RM or heavy resistance, with three sets of each exercise and short, 1-minute, rest periods)

–Supplement diet with carbohydrates and protein before and workouts

What Happens If Your Body Produces Too Much Growth Hormone?

• Pituitary Gigantism

• Characterized by too much growth hormone being secreted before the end of the growth phase

• As a result, you will continue to grow and grow. She is 7 feet 8 inches tall

What Happens If Your Body Produces Too Much Growth Hormone?

• Can result in Acromegaly-enlargement of the hands, feet, and jaw

• Can affect adults in middle age (Andre the Giant)

• Can lead to heart failure, kidney failure, arthritis, and loss of vision

Insulin • A polypeptide hormone secreted

from the pancreas that moves glucose from the blood stream into individual cells–The cells of our body use glucose

as a source of energy for movement, growth, repair, and other functions

–It is released when the body’s blood glucose levels rise

Insulin • Insulin has both positive and negative

effects on how a body looks

–It works to increase protein synthesis, causing muscles to grow

–But it can also enhance body fat levels

–Excessive insulin can also reduce testosterone and GH levels

The Actions of Insulin On Cells• Good for how we look

–Increased glycogen synthesis – insulin forces the storage of glucose in liver and muscle cells in the form of glycogen

–Increased amino acid uptake – forces cells to absorb circulating amino acids; lack of insulin inhibits absorption.

–Decreased proteinolysis – forces reduction of protein degradation; lack of insulin increases protein degradation.

The Actions of Insulin On cells• Bad for how we look

–Insulin stimulates lipogenesis and diminishes lipolysis

–Lipogenesis:

• The conversion of carbohydrates into fat

–Lipolysis:

• The breakdown of fat stored in fat cells

Insulin-Like Growth Factor• Polypeptide hormone

• Secreted by the liver when the liver is stimulated by growth hormone

• Exercise– Results in acute increases in blood

levels

– Multiple-sets, heavy resistance exercise

Catabolic Hormones• Tend to degrade protein synthesis to support glucose synthesis

–Cortisol

–Catacholamines

Cortisol• Released from the adrenal glands• Steroidal• Primary hormone for increasing carbohydrate

metabolism and production• Known as the “Stress Hormone”

• Increases blood pressure and blood sugar and suppresses the immune system

• The major catabolic effects to muscles are:• Converts amino acids to carbohydrates• Increases levels of enzymes that break down

proteins• Inhibits protein synthesis

Cortisol and Exercise• Increases with resistance exercise

• Training may reduce the negative effects of this increase

• High volume, large muscle groups, and short rest periods result in increased serum cortisol values

• Chronic high levels of cortisol may have adverse catabolic effects, acute increases may contribute to the remodeling of muscle tissue

Catecholamines• A group of non-steroidal

hormones:

– Epinephrine

– Norepinephrine

– Dopamine

• Released from the adrenal glands during periods of physical and emotional stress

Epinephrine and Norepinephrine• Epinephrine (also called adrenaline) :

– Fight-or-Flight hormone

– Increases blood flow to muscles and brain

– Dilates pupils

– Increases heart rate and force of heart contractions,

– Helps with conversion of glycogen to glucose in the liver

• Norepinephrine:

– Increases blood pressure

– Constricts blood vessels

Dopamine• Secreted by the hypothalamus and

adrenal glands

• Controls emotion, pleasure, and pain

• Controls voluntary movement-especially balanced and controlled movements

• Deficiency of dopamine may cause Parkinson’s Disease- an individual has impaired balance and coordination, tremors, and difficulty walking

(Michael J. Fox has Parkinson’s Disease)

Catecholamines• Important for temporary bouts of

strength and power–Increase muscle contraction rate–Increase blood pressure–Increase energy availability–Increase blood flow–Regulate secretion rates of other

hormones, such as testosterone

Catecholamines• Fight or flight response causes

elevated stress levels

•Increases cortisol release

•Lowered immune function

•Lowered release of other anabolic hormones

Resistance Training • Catecholamines appear to reflect the severe

demands and physical stress of resistance exercise– High intensity (10 RM), short rest (10-60

seconds between sets and exercises), and a heavy exercise routine (10 exercises, three sets) was shown to maintain increased catecholamine levels for five minutes into recovery

– If training is not varied, continued stress keeps the adrenal gland engaged and recovery is delayed

Resistance Training • Epinephrine has been correlated to lactate

concentrations with exercise stress

• Adrenal responses are not involved in the recovery process until the stress is removed (rest periods)

• The key to all of this that if you want to get optimal results, you need to vary your workouts (sets, reps, intensity, rest intervals)