how exercise effects the endocrine system

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					                          Endocrine Responses to Resistance Exercise
                                         Chapter 6


•       What is the main concept of this chapter?




                                          Endocrine system
•       Vital role in the adaptation to stress
•       Hans Selye’s General Adaptation Syndrome
    •   stress followed by a period of adaptation or improvement in the function
    •   adaptation plateaus
    •   if stimulus continues it may destroy the organism
•       Removal of the stress allows recovery and improved function.

                                       Endocrine system
•       Training Programs provide:
    •   Specific tissue adaptations in response to hormones
        •       Muscle and connective tissue growth
    •   Type of resistance training is the key
    •   Crucial to understand the natural anabolic process

                          Synthesis, Storage, and Secretion of Hormones
•       Hormones: chemical messengers
    • synthesized, stored and released into the blood by endocrine glands and other specialized
    cells.
•       Neurons:
    • synthesize, store and secrete neurotransmitters
•       Endocrine glands:
    • signaled to secrete hormones by chemical or neural stimulation
                                        Multiple functions
 Example: testosterone interacts with almost every tissue in the body; muscle, bone, connective
     tissue, kidney, and liver.
Multiple physiological roles; regulating reproduction; maintenance of the internal environment;
     energy production, utilization, and storage; and growth and development.
Paracrine vs. autocrine mechanisms
                             Muscle: Target for Hormone Interactions
•       Muscle cell protein
    • controlled by many nuclei in the cell.
•       Muscle remodeling:
    • disruption & damage of muscle
    • inflammation, hormonal actions, & synthesis of new proteins
•       Inflammatory process involves the immune system under endocrine control
                                Changes due to resistance training
•       Stimulus of contractile proteins
    •   Actin & myosin
    •   Quality & quantity of muscle is altered
•       Heavy-chain myosin proteins
    •   type IIb to IIa
•       Non-contractile proteins
    •   changed in order to establish structural integrity.
                                Changes due to resistance training
•       Degradation & synthesis
    •   Type I fibers depend on the reduction of protein degradation
    •   Type II fibers depend on an increase in size; hypertrophy
•       Hormones are an integral part of protein metabolism
                                         In-class writing
•       List the primary anabolic hormones.
                                          Hormones




                      Role of Receptors in Mediating Hormonal Changes
•       Hormone influences DNA
•       Receptors:
    •   Binding proteins – mobile
    •   Polypeptide – cell membrane
    •   Steroid – DNA receptor
•       Lock-and-key theory
•       Cross-reactivity
    •   receptor is partially activated with a non-specific hormone; allosteric reactions

                      Role of Receptors in Mediating Hormonal Changes
•       Hormones attach to the receptors causing inhibition or facilitation of protein synthesis
•       Maximum protein added to muscle fiber: Adaptation
    •   Down regulation
    •   Receptors unresponsive to the hormone
    •   Binding sensitivity:
        •        Testosterone, as a result of exercise, affects only the number of receptors sites
        but not sensitivity
                            Steroid Hormones vs. Polypeptide Hormones
•       Steroid Hormone Interactions
    •   adrenal cortex and gonads are soluble and diffuse passively across sarcolemma
    •   Interaction at the genetic level of the muscle cell
                                 Polypeptide Hormone Interactions
•       Amino acids:
    •   growth hormone & insulin
    •   bind to receptors in the blood or in the cell membrane of the target tissue
    •   different receptor domains; internal, external, or integrated
    •   Not fat soluble
        •        Need secondary messengers to relay message to cell nucleus/DNA
                                 Polypeptide Hormone Interactions
•       Cyclic AMP-dependent signaling pathway
•       Cytokine-activated JAK/STAT signaling pathway




                         Heavy Resistance Exercise and Hormonal Increases
•        Increase in anabolic hormone levels
•        Neural stimulation from an alpha motor neuron to a muscle causes other signals from
brain (electrical, chemical, hormonal) to a number of endocrine glands.
•        Hormones are secreted during and after the exercise bout
                         Heavy Resistance Exercise and Hormonal Increases
•        Stress & hormonal responses
    • combine to shape the tissues’ adaptive response to a specific training program
    • Muscle fibers are stimulated and forces are placed on the sarcolemmas of the fibers
    • Stress alters sarcolemma’s permeability to nutrients and affects sensitivity and synthesis
    of receptors in the membrane
                         Heavy Resistance Exercise and Hormonal Increases
•        Inflammatory:
    • tissue damage & repair
•        Specific force:
    produced in the activated fibers stimulates receptor and membrane sensitivities to anabolic
       factors
•        Remodeling - recovery
    • Synthesis of actin and myosin and a reduction of protein degradation
•        Catabolism occurs if stress is too great.
                                           Potential growth
•        Only muscle fibers that are activated by resistance training are subject to adaptation
•       Hormonal interactions
    •   related size of the fibers
    •   dictated by loads, intensity & exercise angles
•       Not all motor units in a muscle will be stimulated - heterogeneity
•       Volume of work and type of protocol
    • Essential for hormonal changes
                               Mechanisms of Hormonal Interactions
•       Controlling factors:
    • Increased concentration of blood levels of hormones increases probability of interaction
    with receptors.
    • Genetic potential limits size of muscle.
    • Adaptations to heavy resistance exercise is anabolic and related to increases in muscle
    size.
    • Inappropriate exercise prescriptions:
        •        catabolic effect & ineffective training program
                                         Controlling factors
•       Force production improvements can be explained by:
    • hypertrophy
    • neural factors integrated with the hormonal factors
•       Hormonal mechanisms different for men vs. women
    • Testosterone
•       Muscle size & strength:
    • Program design, age, sex, genetics, & adaptation potential

                             Hormonal Changes in Peripheral Blood
•       Blood drawing: athletes
    •   Measure hormone concentrations
    •   What is a limiting factor?
•       Physiological mechanisms
    •   Fluid volume shifts
    •   Tissue clearance rates
    •   Hormonal degradation
                             Hormonal Changes in Peripheral Blood
•       Venous pooling of blood
•       Interactions with binding proteins in the blood
•       Receptor interactions
    •   Produces the final effect in muscle
                               Adaptations of the Endocrine System
                                            Homeostasis

                                   Primary Anabolic Hormones
•       Testosterone, insulin-like growth hormone, growth hormone, insulin, & thyroid
•       Testosterone:
    •   primary hormone - skeletal muscle
•       Dihydrotestosterone:
    •   primary androgen that interacts with sex-linked tissues
                                  Primary Anabolic Hormones
•       Testosterone:
    • direct and indirect effects on muscle tissue
    • Promotes GH responses in the pituitary
        •       Influences protein synthesis
    • Influences nervous system:
        •       Increasing amount of neurotransmitters
    • Interact with the muscle itself
    • Transported from testes in men, ovaries and adrenal glands in women
        •       Transport protein     membrane or cytoplasm
        •       Migrates to nucleus = protein synthesis
                                  Primary Anabolic Hormones
•       Increases of testosterone
    • Men & women during and following high-intensity aerobic endurance and resistance
    exercise
    • Balance catabolism – endurance trn

                                            Testosterone
•       What are 4 exercise variables that influence testosterone production?




                                Testosterone Responses in Women
•       Concentration about 1/15th to 1/20th that of men.
•       No acute increase in testosterone after resistance training (figure 6.9)

                               Training Adaptations of Testosterone
•       Training time
•       Experience
    •   Influence resting & exercise induced testosterone
•       Elite weight lifters:
    •   Concomitant increase in LH and FSH, higher brain regulators of testosterone
•       May have a role in the NS by augmenting neural adaptations
                                          Growth Hormone
•       Anterior Pituitary gland
    •   secretes GH (somatotropin)
    •   Enhances cellular amino acid uptake
    •   Protein synthesis in muscle
•       Direct effect
•       Through IGF-I stimulation
    •   Liver or nonhepatic cells (i.e. fat)
•       Many different target tissues

                                     Physiological roles of GH




                        The Efficacy of Pharmacological Growth Hormone
•       GH treatment:
    •   not effective in causing strength increases
    •   Involvement of total motor unit is necessary, even though there may be hypertrophy.
                               Growth Hormone Responses to Stress
•       GH increases:
    •   Depend on load, rest, & volume
    •   Hyperventilation, hypoxia
    •   Specific stresses
        •       High loads, low reps, short rest periods
        •       Example: 1-minute rest, 10 RM, 3 sets

                             Growth Hormone Responses in Women
•       Higher blood levels of GH than men throughout the menstrual cycle
•       Heavy resistance training
    •   5RM, long rest periods (>3 min)
    •   No increase in GH
    •   10 RM, short rest periods (1 min)
    •   Significant increases in serum GH
•       Exercise protocol periodization
    •   Menstrual cycle alters GH response to training
    •   More research needed
                       Insulin-like Growth Factors & Training Adaptations
•       IGFs – polypeptides
    • Liver secretes IGFs after GH stimulates liver-cell DNA
    • 8-29 hours
    • Circulate in blood attached to binding proteins (6 types)
    • Response to resistance training:
    • Synthesize protein
    • Interacts with other hormones
    • Contributes to muscle hypertrophy and increases in strength
                       Insulin-like Growth Factors & Training Adaptations
•       Acute increases in IGF may be due to disruption of the muscle and fat cells from
exercise
•       Amount of increase depends on starting concentration:
    • increase in IGF if basal concentrations are low
•       Nutritional considerations
    • High caloric load
    • Before & after workout

                                        Adrenal Hormones
•       Cortisol
    •   Glucocorticoid: primary signal for CHO metabolism and glycogen stores in muscle
    •   glycogen stores low in muscle
        •        stimulates catabolic reactions of protein to provide amino acids for conversion to
        glucose
    •   Increases the level of proteolytic enzymes (breakdown proteins)
    •   Inhibits protein synthesis (glucose sparing)
    •   More effect on type II fibers ( protein)
                                              Cortisol
•       Joint immobilization, disease, injury, starvation
    •   cortisol starts protein degradation
    •   Testosterone and insulin block the catabolic effects of cortisol
    •   Acute increases of cortisol following exercise
        •        inflammatory response to tissue remodeling
                              Resistance Exercise Responses of Cortisol
•       Resistance training
    •   Rest periods short ,total volume high
•       Training effects:
    •   Testosterone disinhibits cortisol even though the concentration increases
•       Testosterone/cortisol ratio
    •   anabolic-catabolic status of the body - limited success
                                           Catecholamines
•       Epinephrine, norepinephrine and dopamine
    •   Secreted - adrenal medulla
•       Strength & power expression
    •   NS motor stimulators
    •   Peripheral vascular dilators
    •   Enhanced enzyme systems in muscles
•       Stimulate other anabolic reactions
                                  Epinephrine and Norepinephrine
•        force production via central mechanisms
•        metabolic enzyme activity
•        muscle contraction rate
•        BP & blood flow
•        energy availability
•        secretion rates of other hormones such as testosterone
                                       Training Adaptations
•       Epinephrine:
    • metabolic control
    • force production
    • response mechanisms other hormones (testosterone, GH, IGFs)
    • Stimulation of the catecholamines
        •        1st endocrine mechanisms response to resistance exercise
                                  Endocrine System & Training
                                          General Concepts
    • Recruit more muscle fibers
        •        potential remodeling process enhanced in the whole muscle.
    • Only muscle fibers activated can adapt
        •        Including hormonal adaptations to stress
                                  Endocrine System & Training
                                          Specific Concepts
•       Increase Serum Testosterone Concentrations
    • Use large muscle group exercises (deadlift, power cleans, squats) or,
    • Use heavy resistance (85% to 95% of 1RM), or
    • Use moderate to high volume of exercise, achieved with multiple sets or multiple
    exercises, or
    • Use short rest intervals (60-90s)
                                  Endocrine System & Training
•       Increase Growth Hormone Levels
    • Workouts with high lactate concentrations and associated acid-base disruptions
        •        high intensity (10RM, or heavy resistance) with three sets of each exercise (high
        total work) and short (1 minute) rest periods, or
    • Supplement diet with CHO and protein before and after workouts
                                    Endocrine System & Training
•       Optimize Responses of Adrenal Hormones
    • High volume, large muscle groups, & short rest periods, vary the training protocol and
    the rest period length and volume to allow the adrenal gland to engage in recovery processes
    (secreting less cortisol) and to prevent chronic catabolic responses of cortisol.
    • Stress of the exercise will not result in overuse or overtraining
                                       Possible Exam Question
•       What are the primary anabolic hormones for muscle? Summarize how would you use
your knowledge of these hormones to design a resistance training program for Mr. G? What
variables would you manipulate to help him achieve his goal?
    • 28 years old – recreational lifter (2x week)
    • Goal: increase chest and back muscle size and strength.

				
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