Chapter 4 - Endocrine Responses to Resistance Exercise Flashcards
General Adaptation Syndrome
How the adrenal gland responds to a noxious stimulus (stressor).
Increase in resistance to the stress is referred to as adaptation.
When the stressor is exercise, it is called training adaptation.
Hormones
Chemical messengers that are synthesized, stored, and released into the blood by endocrine glands and certain other cells.
Principle Endocrine Glands and Glands that Secrete Hormones
Hypothalamus Pituitary Gland Thyroid Gland Parathyroid Gland Heart Liver Adrenal Gland Pancreas Kidneys Testes (male) Overies (female)
Muscle as a target for hormone interactions
Hormonal mechanisms are a part of an integrated signaling system that mediates change in the metabolic and cellular process of muscle as a result of resistance exercise and training.
Hormones are intimately involved with protein synthesis and degradation mechanisms that are part of muscle adaptation to resistance exercise.
Anabolic Hormones
Hormones that promote tissue building, such as: insulin, insulin-like growth factors (IGFs), testosterone, and growth hormone.
Catabolic Hormones
Can degrade cell protein, such as: cortisol and progesterone.
Role of Receptors in Mediating Hormonal Changes
The signal from a hormone (and thereby its biological effect) is relayed only to cells that express the receptor for that specific hormone.
Lock-and-Key Theory
Receptor is the lock and the hormone is the key
Down-regulation
Inability of a hormone to interact with a receptor.
When adaptation is not longer possible (i.e. the maximal amount of protein has been added to the muscle fiber) or “overstimulation” by a hormone has occurred, receptors can become less responsive or even non responsive to a specific hormone, preventing it from stimulating further action in the cell.
Categories of Hormones
Steroid
Polypeptide (aka Peptide)
Amine
Steroid Hormone Interaction
Includes; cortisol, testosterone, and estradiol.
Fat soluble and passively diffuse across sarcolemma of a muscle fiber.
Binds with its receptor to form a Hormone-Receptor Complex (H-RC), causing shift in receptor (aka receptor activation.
H-RC binds with another H-RC a moves to cell’s nucleus and “open” the double stranded DNA in order to expose transcriptional units that code for the synthesis of specific proteins.
RNA polymerase II binds to the promoter associated with specific upstream regulatory elements for H-RC.
RNA polymerase II transcribe gene by coding for the protein dictated by steroid hormone.
Messenger RNA (mRNA) is processed and moves into sarcoplasm of cell, where it’s translated by the ribosome into the specific protein.
Polypeptide Hormone Interaction
Made up of chains of amino acids (ex. growth hormone and insulin).
They’re not fat soluble and thus cannot cross cell membrane.
Secondary messengers are inside cell are activated by conformational change in receptor.
In general, the signaling cascades initiated by polypeptide hormones affect metabolic process, DNA transcription, or mRNA translation initiation at the ribosome.
Ex. One of the signals from insulin induces translocation of specific glucose transporters (GLUT4) from cytosol to cell membrane, allowing for increase glucose uptake.
Amine Hormone Interactions
Synthesized from amino acid tyrosine (e.g., epinephrine, norepinephrine, and dopamine) or tryptophan (e.g., serotonin).
Similar to Polypeptide hormones, in which the bind to membrane receptors and act via secondary messengers. However, they are not regulated by negative feedback.
Heavy Resistance Exercise and Hormonal Increases
Long-term consistent RT brings significant adaptive responses (enhanced size, strength and power) of trained muscles.
Physiological systems, including endocrine, are sensitive to needs of activated muscle, and therefore the type of exercise protocol determines the extent of a given system’s involvement (hormonal response. to exercise protocol).
1-2 heavy RT sessions can increase number of androgen receptors (testosterone receptor) in muscle.
If stress is too great, catabolic actions in muscle occur (down regulation).
Mechanisms of Hormonal Interactions
Interactions with receptor are greater when exercise acutely increases blood concentrations of hormones.
Receptors are LESS sensitive when:
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.
Mistakes are made in exercise prescriptions.
Hormonal Changes in Peripheral Blood
Contributing mechanisms includes: 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.
Hormone responses are tightly linked to the characteristics of the resistance exercise protocol.
Potential Types of Adaptations of the Endocrine System from Resistance Training
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-tiissue fluid shift occurs with exercise stress.
How many receptors are in the tissue.
Primary Anabolic Hormones
Testosterone
Growth hormone (GH)
Insulin-like growth factors (IGFs).
Testosterone
Primary androgen hormone that interacts with skeletal muscle tissues.
Effects of Testosterone on Muscle Tissues
Causes GH release that leads to protein synthesis, increased strength and size of skeletal muscle, increased force production potential and muscle mass.
Large muscle group exercises result in acute increased serum total testosterone concentrations in men.
Diurnal variations (normal fluctuations of hormone levels during the day) of Testosterone – Men and Women
Men: concentration typically highest in the morning and drop as the day goes on, but increases can occur at any point with exercise.
However, an already small resting concentration of testosterone leads to smaller magnitude of change with exercise.
Women: there are lower concentrations and little variation during the day.
However, the response of their androgen receptors is very dynamic with a much faster up regulation than in men, likely to better use the amount of testosterone with a RT stimulus.
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, and increases occur after resistance training, they are small increases.
Training Adaptations of Testosterone
It appears that training time and experience may be very important factors in altering the resting and exercise induced concentrations.
Growth Hormone (GH)
Secreted by 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 alters by age, gender, sleep, nutrition, alcohol consumption, and exercise.
Efficacy of Pharmacological GH
Use of has unknown and unpredictable results.
GH Responses to Stress
Responds to exercise stressors (ex. resistance training).
Response depends on load, rest, and volume of exercise (ex. less rest = high GH; 10RM = higher GH; 3 sets = higher GH).
GH release is affected by type of resistance training protocol used (duration and rest periods).
Short rest period types of workouts result in greater serum concentrations compared to long rest protocols of similar total work.
GH Responses in Women
GH concentrations and responses to exercise vary with menstrual phase.
Women have higher blood levels of GH than men.
Training Adaptations of GH
There is little change in single measurement of resting GH concentrations in resistance-trained individuals.
Training-related changes in GH include a reduction in GH response to an absolute exercise stress and alterations in GH pulsatility characteristics.
Insulin-Like Growth Factors (IGF)
IGF-1 is most studied because of its role in protein anabolism.
Exercise results in acute increases in blood levels of IGF-1.
Training Adaptations of Insulin-Like Growth Factors
Changes in IGF-1 appear to be based on the starting concentrations before training.
If basal concentrations are low, IGF-1 increases.
If basal concentrations are high, there’s no change or it decreases.
Adrenal Hormones
Cortisol Catecholamines (epinephrine, norepinephrine, dopamine).
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 RT.
Training may reduce negative effects of this increase.
Vast differences are observed in the physiological role of cortisol in acute v. chronic responses.
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.
Catecholamines
Epinephrine
Norepinephrine
Dopamine
Role of Catecholamines
Increase force production via central mechanisms and increased metabolic enzyme activity.
Increase muscle concentration rate.
Increase blood pressure.
Increase energy availability.
Increase blood flow.
Augment secretion rates of other hormones, such as testosterone.
Training Adaptations of Catecholamines
Heavy RT has been shown to increase the ability of an athlete to secrete greater amounts of epinephrine during maximal exercise.
Training protocols must be varied t allow the adrenal gland to engage in recovery process and to prevent the secondary responses of cortisol, which can have negative effects on the immune system and protein structures.
To increase Testosterone – Manipulating the Endocrine System with RT
Large muscle exercises (deadlifts, squats, power clean).
Heavy resistance (85-95% 1RM).
Moderate-High volume of exercise achieved with multiple sets or exercise.
Short rest intervals (30s to 1 min).
2+ years of RT experience.
To increase GH – Manipulating the Endocrine System with RT
Use high intensity (10RM or heavy resistance).
3 Sets of each exercise (high total work).
Short (1 min) rest periods.
Supplement diet with carbohydrate and protein before and after workout.
Optimal Response of Adrenal Hormones
High volume.
Large muscle groups.
Short rest periods.
Vary all these factors to allow adrenal gland to engage in recovery process.
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 Rt 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 RT.
