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66C H A P T E R
Endocrine Responses to Resistance ExerciseEndocrine Responses to Resistance Exercise
Chapter Outline
Synthesis, storage, and secretion of hormones
Muscle as the target for hormone interactions
The role of receptors in mediating hormonal changes
Steroid hormones versus polypeptide hormones
Heavy resistance exercise and hormonal increases
Mechanisms of hormonal interactions
Hormonal changes in peripheral blood
Adaptations in the endocrine system
The primary anabolic hormones
The adrenal hormones
Other hormonal considerations
Endocrine Glands of the BodyEndocrine Glands of the Body
Hormones and Resistance Training
• Resistance training imposes a natural hormonal stimulus
• The type of resistance training dictates the nature of the hormonal response.
• Tissue adaptations are influenced by changes in circulating hormonal concentrations.
• Hormones play a vital role in the organisms response to a bout of exercise.
Definitions
• Hormones: chemical messengers that are synthesized, stored in, and released into the blood by endocrine glands.
• Endocrine glands: body structures specialized for secretion of hormones.
• Neuroendcrinology: describes the relationship between chemical substances that have both neural and hormonal functions.
• Target Tissues (peptide hormones): hormones in the blood carry messages to hormone specific receptors.
• Steroid Hormones: hormones that directly affect the DNA in the nucleus of the cell.
Autocrine vs Paracrine Secretion
• Autocrine secretion of a hormone means the cell releases the hormone itself (automatic). It may be stimulated to do so by an external stimulus (hormone).• Ex. In response to an exercise bout, insulin-like growth
factor I (IGF-I) is released inside the muscle cell to cause the cell to produce more myofibrils in response to the exercise.
• Paracrine secretion involves the release of a hormone to interact adjacent cells, without a need for circulation of the hormone in the blood stream.
Binding Proteins?
• Binding proteins whether circulating in the blood or bond to a cell, affect endocrine function as a kind of receptor.
• Binding proteins carry both peptide and steroid hormones.
• Binding proteins in the blood protect the hormones from degradation during circulation.
• Most hormones are not active until separated from their binding proteins.
• Some hormone binding proteins may have direct biological actions.
Two Main Categories of Hormones: Steroid & Polypeptide
• Steroids are soluble and they passively diffuse across the sarcolemma.
• Polypeptides are not fat soluble and they cannot penetrate the sarcolemma.
• Polypeptides must rely on secondary messengers (STAT) to get their message to the cell nucleus and DNA.
Heavy Resistance Exercise & Hormonal Increases• Long term heavy resistance training brings about adaptive
responses: enhanced size, strength & power of the muscle fibers stressed.
• Resistance training causes an increase in anabolic hormonal levels that enhance the development of muscle proteins.
• Hormones are secreted during and after exercise.• Acute secretions provide information on amount of stress
(epinephrine), metabolic demands (insulin), and need for change in resting metabolism.
• Local tissue damage induces a local inflammatory response.• Only the tissues exercises will receive these messages and
adaptive changes in the muscle proteins.• If the stress is too great (Overtraining), catabolic actions
may occur, as a result of the inability of anabolic hormones to bind to receptors (down regulation) in the muscle tissue.
Hormonal Changes in Peripheral Blood• Fluid Volume Shifts: Exercise causes a shift of body fluids
from the blood to the cells. This shift in fluid results in an increased concentration of hormones in the blood, which can affect the receptor interactions.
• Tissue Clearance Rates: Changes in the time taken for hormones to pass thru tissue such as the liver affect the time for the hormone to reach its final target receptor.
• Hormonal Degradation: The breakdown of hormones.
• Venous Pooling of Blood: Areas of venous pooling can increase the exposure of hormones to receptors.
• Interactions with Binding Proteins in the Blood: Free hormones and protein-bond hormones interact differently.
• Receptor Interactions: Changes in hormone concentrations can alter the receptor response.
Adaptations in the Endocrine System
• Amount of synthesis and storage of hormones• Transport of hormones via binding proteins• Time needed for clearance of hormones through liver and
other tissues.• Amount of hormonal degradation that takes place over
time.• How much blood-to-tissue shift occurs with exercise.• How tightly the hormone binds to its receptor.• How many receptors are in the tissue.• The magnitude of the signal sent to the cell via secondary
messenger.• The degree of interaction with the nucleus (how much
protein to produce).
The force produced in the activated fibers
stimulates receptor and membrane sensitivities
to anabolic factors, including hormones, which
lead to muscle growth and strength changes.
Hormone responses are tightly
linked to the characteristics of the
resistance exercise protocol.
Large-muscle group exercises
result in acute increased serum
total testosterone concentrations
in men.
Growth hormone is important for a child’s
normal development 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 hypertrophy with less force
production than results from exercise-induced
hypertrophy.
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 modeling of
muscle tissue.
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 negatively
affect the immune system and protein stuctures.