chapter
Endocrine
4
Responses to Resistance
Exercise
Endocrine
Responses
to Resistance
Exercise
William J. Kraemer, PhD, Jakob L. Vingren, PhD, and
Barry A. Spiering, PhD
Chapter Objectives
• Understand basic concepts of endocrinology,
including what hormones are and how they
interact with each other and target tissues
• Explain the physiological roles of anabolic
hormones
• Describe hormonal responses to resistance
exercise
• Develop training programs that demonstrate
an understanding of human endocrine
responses
Key Terms
• hormones: Chemical messengers that are
synthesized, stored, and released into the
blood by endocrine glands and certain other
cells.
• endocrine glands: Body structures specialized
for releasing hormones into the blood.
Synthesis, Storage,
and Secretion of Hormones
• Figure 4.1 (next slide)
– The principal endocrine glands of the body along
with other glands that secrete hormones
Figure 4.1
Muscle as the Target
for Hormone Interactions
• Hormones are intimately involved with
protein synthesis and degradation
mechanisms that are part of muscle
adaptations to resistance exercise.
• This includes both anabolic (promote tissue
building) and catabolic (degrade cell
proteins) hormones.
Roles of Receptors in Mediating
Hormonal Changes
• Lock-and-key theory
– Figure 4.2 (next slide)
• A schematic representation of the classic lock-and-key
theory for hormonal action at the cell receptor level
Figure 4.2
Roles of Receptors in Mediating
Hormonal Changes
• The inability of a hormone to interact with a
receptor is called downregulation.
• Alterations to a receptor’s binding
characteristics or the number of receptors
can be as dramatic in adaptation as the
release of increased amounts of hormone
from an endocrine gland.
Categories of Hormones
• Steroid hormone interactions
– Fat soluble and passively diffuse across the cell
membrane
– Figure 4.3 (next slide)
• Typical steroid migration into a target cell by either
testosterone in skeletal muscle or dihydrotestosterone in
sex-linked tissues. Only one hormone pathway
(testosterone or dihydrotestosterone) is targeted for one
cell, but the two are shown together in this diagram. Each
has different physiological outcomes.
Figure 4.3
Categories of Hormones
• Polypeptide hormone interactions
– Made of chains of amino acids
– Examples: growth hormone and insulin
– Figure 4.4 (next slide)
• Typical polypeptide hormone interaction with a receptor via
the cytokine-activated JAK/STAT signaling pathway
• Although the hormone binds to an external receptor, a
secondary messenger (STAT) is activated that can enter
the cell nucleus.
Figure 4.4
Categories of Hormones
• Amine hormone interactions
– Synthesized from the amino acid tyrosine (e.g.,
epinephrine, dopamine) or tryptophan (serotonin)
– Bind to membranes via secondary messengers
– Not regulated by negative feedback
Heavy Resistance Exercise
and Hormonal Increases
• Hormones are secreted before, during, and
after the resistance exercise bout due to the
physiological stress of resistance exercise.
• As few as one or two heavy resistance
exercise sessions can increase the number
of androgen receptors in the muscle.
Key Point
• The specific force produced in activated
fibers stimulates receptor and membrane
sensitivities to anabolic factors, including
hormones, which leads to muscle growth
and strength changes.
Mechanisms of Hormonal Interactions
• The combination of many different
mechanisms is thought to stimulate
exercise-induced hypertrophy.
• Molecular signaling including hormones is
involved with this process.
• This signaling is influenced by neural
factors that provide important signals to the
skeletal muscle and thus can augment
anabolic processes.
Hormonal Changes
in Peripheral Blood
• Peripheral concentrations of hormones in
the blood do not indicate the status of the
various receptor populations or the effects
of a hormone within the cell.
• It is typically assumed, however, that large
increases in hormone concentration
indicate higher probabilities for interactions
with receptors.
(continued)
Hormonal Changes
in Peripheral Blood (continued)
• Physiological mechanisms that contribute to
changes in peripheral blood concentrations
of hormones with exercise:
–
–
–
–
–
Circadian pattern
Fluid volume shifts
Tissue clearance rates
Venous pooling of blood
Hormone interactions with binding proteins
Key Point
• Hormone responses are tightly linked to the
characteristics of the resistance exercise
protocol.
Adaptations in the Endocrine System
• Examples of the types of adaptations that
are possible:
– Amount of synthesis and storage of hormones
– Time needed for clearance of hormones through
liver and other tissues
– How many receptors are in the tissue
– Changes in the contents of the secretory cells in a
gland
– Degree of interaction with the cell nucleus
Primary Anabolic Hormones
• Testosterone
– Heavy resistance training using one or two
repetitions in low volume, which may not cause any
changes in testosterone concentrations after a
workout, could potentially still increase the absolute
number of receptors and thus binding sites available
to testosterone.
– This effect on receptors has yet to be fully
elucidated.
Key Point
• Large muscle group exercises using an
adequate volume of total work result in
acute increased total testosterone
concentrations in men.
Primary Anabolic Hormones
• Testosterone
– Exercise variables that can increase serum
testosterone concentrations:
•
•
•
•
•
Large muscle group exercises (deadlift, squats)
Heavy resistance (85-95% of 1RM)
Moderate to high volume of exercises
Short rest intervals (30 seconds to 1 minute)
Two years or more of resistance training experience
(continued)
Primary Anabolic Hormones (continued)
• Testosterone
– Free testosterone and sex hormone–binding globulin
• Free testosterone accounts for only 0.5% to 2% of total
testosterone; thus higher total testosterone concentration
allows for more free testosterone.
• Heavy resistance exercise (e.g., six sets of 10 repetitions at
80% of 1RM) can acutely increase free testosterone in men
and women, although the increase is much smaller for
women.
(continued)
Primary Anabolic Hormones (continued)
• Testosterone
– Responses in women
• Women have about 15- to 20-fold lower concentrations of
circulating testosterone than men do.
• The testosterone concentration can vary substantially
between individual women, as some women secrete higher
concentrations of adrenal androgens.
(continued)
Primary Anabolic Hormones (continued)
• Figure 4.5 (next slide)
– Responses to six sets of squats at 80% of 1RM with
2 minutes rest between sets
(a) Total testosterone
(b) Free testosterone in response
– * Indicates a significant increase from preexercise
values.
– # Indicates a significant difference from women at
the corresponding time point.
Figure 4.5(a)
Figure 4.5(b)
Primary Anabolic Hormones
• Testosterone
– Training adaptations
• Testosterone increases in response to the demands of an
exercise protocol, and then the receptors either increase
binding to use the elevated testosterone or they do not due
to a lack of need for the signal to increase muscle-related
metabolism.
• Other receptors on other target tissues (e.g., nervous,
satellite cells) may be more affected at certain time points in
training, depending on the window of adaptation available
in the target tissues.
(continued)
Primary Anabolic Hormones (continued)
• Growth hormone
– Important for the normal development of a child
– Appears to play a vital role in adapting to the stress
of resistance training
– Figure 4.6 (next slide)
• Diagram of growth hormone cybernetics and interactions
Figure 4.6
Primary Anabolic Hormones
• Growth hormone
– Main physiological roles of GH and its superfamily:
•
•
•
•
•
•
Decreases glucose utilization
Increases protein synthesis
Increases collagen synthesis
Stimulates cartilage growth
Enhances immune cell function
Increases lipolysis (fat breakdown)
Key Point
• Growth hormone release is affected by the
type of resistance training protocol used,
including the duration of rest period. Short
rest period types of workouts result in
greater serum concentrations compared to
long rest protocols of similar total work;
however, at present it is not clear how the
various molecular forms (e.g., aggregates
and splice variants) or types of GH are
affected by rest period duration.
Primary Anabolic Hormones
• Growth hormone
– Responses in women
• Hormone concentrations and hormone responses to
exercise vary with menstrual phase.
• The mechanisms of this variation are unclear.
(continued)
Primary Anabolic Hormones (continued)
• Growth hormone
– Training adaptations
• It appears that GH concentrations need to be measured
over longer time periods (2-24 hours) to show whether
changes occur with resistance training.
• The area under the time curve, which includes an array of
pulsatile effects, tells whether changes in release have
occurred.
(continued)
Primary Anabolic Hormones (continued)
• Exercise responses of insulin-like growth
factor
– Figure 4.7 (next slide)
• Responses of insulin-like growth factor I to a multiple-set,
heavy resistance exercise protocol on three consecutive
days with and without nutritional supplementation of
protein-carbohydrate before and during the 1-hour recovery
period
Figure 4.7
Primary Anabolic Hormones
• Training adaptations of insulin-like growth
factor
– Probably reflected in a variety of mechanisms
related to type of IGFs, release, transport, and
receptor interaction.
– Interaction with other anabolic hormones cannot be
ignored, as these often target the same outcome.
– Adaptations to heavy resistance training of IGF-I in
the various tissues still require further investigation.
(continued)
Adrenal Hormones
• Cortisol
– Exerts its major catabolic effects by
• stimulating the conversion of amino acids to carbohydrates,
• increasing the level of proteolytic enzymes (enzymes that
break down proteins),
• inhibiting protein synthesis, and
• suppressing many glucose-dependent processes such as
glycogenesis and immune cell function.
– Has a greater effect on Type II fibers than Type I
fibers.
(continued)
Adrenal Hormones (continued)
• Cortisol
– Resistance exercise responses
• Responds to resistance exercise protocols that create a
dramatic stimulus to anaerobic metabolism.
• Increases in cortisol might not have negative effects in men
after a period of training to which the body has adapted;
adaptation “disinhibits” cortisol at the level of the testis,
thereby maintaining testosterone’s primary influence on its
nuclear receptors.
Key Point
• Resistance exercise protocols that use high
volume, large muscle groups, and short rest
periods result in increased serum cortisol
values. Though chronic high concentrations
of cortisol may have adverse catabolic
effects, acute increases still contribute to
the remodeling of muscle tissue and
maintenance of blood glucose.
Adrenal Hormones
• Catecholamines
– Roles
• Increase force production via central mechanisms and
increased metabolic enzyme activity
• Increase muscle contraction rate
• Increase blood pressure
• Increase energy availability
• Increase muscle blood flow (via vasodilation)
• Augment secretion rates of other hormones, such as
testosterone
(continued)
Adrenal Hormones (continued)
• Catecholamines
– Training adaptations
• Heavy resistance training has been shown to increase the
ability of an athlete to secrete greater amounts of
epinephrine during maximal exercise.
• Because epinephrine is involved in metabolic control, force
production, and the response mechanisms of other
hormones (such as testosterone, GHs, and IGFs),
stimulation of catecholamines is probably one of the first
endocrine mechanisms to occur in response to resistance
exercise.
Other Hormonal Considerations
• Hormones such as insulin, thyroid
hormones, and beta-endorphin have been
implicated in growth, repair, pain analgesia,
and exercise stress mechanisms;
unfortunately, few data are available
concerning their responses and adaptations
to resistance exercise or training.