Endocrine Responses to Resistance Exercise
Chapter Objectives
•Understand basic concepts of endocrinology.
•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 Point
•It has been theorized that the endocrine system can be manipulated naturally with
resistance training to enhance the devel-opment of various target tissues, thereby
improving performance.
Section Outline
•Synthesis, Storage, and Secretion of Hormones
Key Term
•hormones: Chemical messengers that are synthesized, stored, and released into the
blood by endocrine glands and certain other cells.
Glands of the Body
•Figure 3.1 (next slide)
–The principal endocrine glands of the body along with other glands that secrete
hormones
Figure 3.1
Section Outline
•Muscle as the Target for Hormone Interactions
Muscle Cell
•Figure 3.2 (next slide)
–The muscle cell is a multinucleated cell in which each nucleus controls a region of the
muscle protein (called a nuclear domain).
Figure 3.2
Section Outline
•Role of Receptors in Mediating Hormonal Changes
Lock-and-Key Theory
for Hormonal Action
•Figure 3.3 (next slide)
–A schematic representation of the classic lock-and-key theory for hormonal action at the
cell receptor level
Figure 3.3
Androgen Receptor Diagram
•Figure 3.4 (next slide)
–Diagram of a typical androgen receptor on the DNA element in the nucleus
Figure 3.4
Section Outline
•Steroid Hormones Versus Polypeptide Hormones
–Steroid Hormone Interactions
–Polypeptide Hormone Interactions
Steroid Hormones Versus
Polypeptide Hormones
•There are two main categories of hormones:
–Steroid
–Polypeptide (or simply peptide)
Hormone Structure
•Figure 3.5 (next two slides)
–Structure of
•(a) a polypeptide hormone (growth hormone, 22 kDa)
•(b) a steroid hormone (testosterone)
Figure 3.5a
Figure 3.5b
Steroid Hormones Versus
Polypeptide Hormones
•Steroid Hormone Interactions
–A steroid hormone passively diffuses across the sarcolemma of a muscle fiber.
–It binds with its receptor to form a hormone-receptor complex (H-RC).
–H-RC arrives at the genetic material in the cell’s nucleus and “opens” it in order to
expose tran-scriptional units that code for the synthesis of specific proteins.
(continued)
Steroid Hormones Versus
Polypeptide Hormones
•Steroid Hormone Interactions (continued)
–RNA polymerase II binds to the promoter that is associated with the specific upstream
regulatory elements for the H-RC.
–RNA polymerase II transcribes the gene by coding for the protein dictated by the steroid
hormone.
–Messenger RNA (mRNA) is processed and moves into the sarcoplasm of the cell, where
it is translated into protein.
Steroid Migration
•Figure 3.6 (next slide)
–The slide shows 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.
Figure 3.6
Steroid Hormones Versus
Polypeptide Hormones
•Polypeptide Hormone Interactions
–Cyclic adenosine monophosphate-dependent (cyclic AMP-dependent) signaling
pathway
–Cytokine-activated JAK/STAT signaling pathway
–Prototypical growth factor, mitogen-activated signaling pathway
Polypeptide Hormone Interaction
•Figure 3.7 (next slide)
–The slide shows typical polypeptide hormone (growth hormone in this example)
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.
–Tyr-P = tyrosinase related protein
Figure 3.7
Section Outline
•Heavy Resistance Exercise and Hormonal Increases
Key Point
•The specific force produced in activated fibers stimulates receptor and membrane
sensitivities to anabolic factors, including hormones, which lead to muscle growth
and strength changes.
Section Outline
•Mechanisms of Hormonal Interactions
Mechanisms of Hormonal Interactions
•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 exogenous drug use,
and
–mistakes are made in exercise prescriptions.
Section Outline
•Hormonal Changes in Peripheral Blood
Hormonal Changes
in Peripheral Blood
•Mechanisms contributing to changes in peripheral blood concentrations of
hormones:
–Fluid volume shifts
–Tissue clearance rates
–Hormonal degradation
–Venous pooling of blood
–Interactions with binding proteins in the blood
•These mechanisms interact to produce certain concentrations of hormones in the
blood, which influences the potential for interaction with receptors.
Key Point
•Hormone responses are tightly linked to the characteristics of the resistance
exercise protocol.
Section Outline
•Adaptations in the Endocrine System
Adaptations in the Endocrine System
•Examples of the potential types of adaptation with resistance exercise:
–Amount of synthesis and storage of hormones
–Transport of hormones via binding proteins
–Time needed for the clearance of hormones through liver and other tissues
–Amount of hormonal degradation that takes place over a given period of time
–How much blood-to-tissue fluid shift occurs with exercise stress
–How many receptors are in the tissue
Section Outline
•Primary Anabolic Hormones
–Testosterone
•Free Testosterone and Sex Hormone–Binding Globulin
•Testosterone Responses in Women
•Training Adaptations of Testosterone
–Growth Hormone
•Efficacy of Pharmacological Growth Hormone
•Growth Hormone Responses to Stress
•Growth Hormone Responses in Women
•Training Adaptations of Growth Hormone
(continued)
Section Outline (continued)
•Primary Anabolic Hormones
–Insulin-Like Growth Factors
•Exercise Responses of Insulin-Like Growth Factors
•Training Adaptations of Insulin-Like Growth Factors
Primary Anabolic Hormones
•There are three primary hormones involved in muscle tissue growth and
remodeling:
–Testosterone
–Growth hormone (GH)
–Insulin-like growth factors (IGFs)
Primary Anabolic Hormones
•Testosterone
–The primary androgen hormone that interacts with skeletal muscle tissue
–Effects on muscle tissue: GH responses that lead to protein synthesis, increased strength
and size of skeletal muscle, increased force production potential and muscle mass
–Diurnal 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.
Biosynthesis of Testosterone
From Cholesterol
•Figure 3.8 (next slide)
–The series of chemical reactions in the biosynthesis of testosterone from cholesterol
Figure 3.8
Key Point
•Large muscle group exercises result in acute increased serum total testosterone
concentrations in men.
Primary Anabolic Hormones
•Testosterone
–Free Testosterone and Sex Hormone–Binding Globulin
•A higher total (bound) testosterone level allows for the potential of more free
testosterone.
•The free hormone hypothesis states that only the free hormone interacts with target
tissues.
–Testosterone Responses in Women
•Women have 15- to 20-fold lower concentrations of testosterone than men do, and if
acute increases occur after a resistance training workout, they are small.
–Training Adaptations of Testosterone
Serum Testosterone
Responses to Exercise
•Figure 3.9 (next slide)
–Male (green bars) and female (gold bars) serum testosterone responses to two exercise
programs:
•(a) a protocol entailing eight exercises using 5RM and
3-minute rest periods between sets and exercises
•(b) a program that called for eight exercises using 10RM and 1-minute rest periods
between sets and exercises
(the total work for the second protocol was higher)
–* = significantly above preexercise levels
–+ = significantly above the other group
Figure 3.9
Primary Anabolic Hormones
•Growth Hormone
–Secreted by the pituitary gland
–Interacts directly with target tissues, which include bone, immune cells, skeletal muscle,
fat cells, and liver tissue
–Regulated by neuroendocrine feedback mechanisms and mediated by secondary
hormones
–GH release patterns altered by age, gender, sleep, nutrition, alcohol consumption, and
exercise
Growth Hormone Cybernetics
and Interactions
•Figure 3.10 (next slide)
–Diagram of growth hormone cybernetics and interactions
Figure 3.10
Primary Anabolic Hormones
•Growth Hormone
–Efficacy of Pharmacological Growth Hormone
•Pharmacological use of GH has unknown and unpredictable results.
–Growth Hormone Responses to Stress
•GH responds to exercise stressors, including resistance exercise.
•GH response depends on load, rest, and volume of exercise.
Primary Anabolic Hormones
•Growth Hormone
–Growth Hormone Responses in Women
•GH concentrations and responses to exercise vary with menstrual phase.
•Women have higher blood levels of GH than do men.
–Training Adaptations of Growth Hormone
•There is little change in single measurements of resting GH concentrations in resistancetrained individuals.
•Training-related changes in GH include a reduction in GH response to an absolute
exercise stress and alterations in GH pulsatility characteristics.
Key Point
•Growth hormone is important for the normal development of a child and appears
to play a vital role in adapting to the stress of resistance training. However, GH
injections result in a wide variety of secondary effects not related to changes in
muscle size or strength and can, in fact, result in hyper-trophy with less force
production than occurs with exercise-induced hypertrophy.
Primary Anabolic Hormones
•Insulin-Like Growth Factors
–Exercise Responses of Insulin-Like Growth Factors
•Insulin-like growth factor I (IGF-I) is most studied because of its role in protein
anabolism.
•Exercise results in acute increases in blood levels of IGF-I.
Insulin-Like Growth
Factor I and Exercise
•Figure 3.11 (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 (i.e., Mass Fuel) before and during the 1-hour recovery period
–†p < .05 from corresponding placebo value
Figure 3.11
Primary Anabolic Hormones
•Insulin-Like Growth Factors
–Training Adaptations of Insulin-Like Growth Factors
•Changes in IGF-I appear to be based on the starting concentrations before training.
–If basal concentrations are low, IGF-I increases.
–If basal concentrations are high, there is no change or it decreases.
Section Outline
•The Adrenal Hormones
–Cortisol
•Role of Cortisol
•Resistance Exercise Responses of Cortisol
–Catecholamines
•Role of Catecholamines
•Training Adaptations of Catecholamines
The Adrenal Hormones
•Cortisol
–Role of Cortisol
•Catabolic effects
–Converts
amino acids to carbohydrates, increases the level
of enzymes that break down proteins, and inhibits protein synthesis
–Resistance Exercise Responses of Cortisol
•Cortisol increases with resistance exercise.
•Training may reduce the negative effects of this increase.
•Vast differences are observed in the physiological role of cortisol in acute versus chronic
responses.
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 levels of
cortisol may have adverse catabolic effects, acute increases may contribute to the
remodeling of muscle tissue.
The Adrenal Hormones
•Catecholamines
–Role of Catecholamines
•Increase force production via central mechanisms and increased metabolic enzyme
activity
•Increase muscle contraction rate
•Increase blood pressure
•Increase energy availability
•Increase blood flow
•Augment secretion rates of other hormones, such as testosterone
–Training Adaptations of Catecholamines
Key Point
•Training protocols must be varied to allow the adrenal gland to engage in recovery
processes and to prevent the secondary responses of cortisol, which can have
negative effects on the immune system and protein structures.
Section Outline
•Other Hormonal Considerations
Other Hormonal Considerations
•Many other hormones create an optimal environment
in which the primary hormonal actions can take place.
•Insulin, thyroid hormones, and beta-endorphins affect growth, repair, and exercise stress
mechanisms.
•Improvements in insulin resistance with resistance training may reflect only an acute
effect from the most recent exercise session.
•Researchers have found slight, nonsignificant decreases in serum concentrations of total
and free thyroxine after 20 weeks of resistance training.