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.