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
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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
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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
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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 nonresponsive 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
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Activated to help with recovery and adaptation to
stress (resistance training)
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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)
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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
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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 lactateconcentrations and associated acidbase 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
Acromegalyenlargement 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)