ACE s Essentials of Exercise Science for Fitness Professionals Chapter 2: Hormones
Learning Objectives This chapter covers how the body responds to the demands of exercise at the cellular level and the physiological adaptations that occur with specific training programs. Upon completion of this chapter, you will be able to: List some of the hormonal responses to exercise
The Endocrine System The endocrine system, which is made up of various glands throughout the body, is responsible for regulating bodily activities through the production of hormones. The principal glands are as follows: Pituitary Thyroid Parathyroids Adrenals Paradrenals Gonads
Hormonal response to exercise Learning activity: Your group will be assigned a hormone or related hormones. Research and be prepared to present the following information: Where is the hormone made in the body? What does it do (in general)? Describe its relationship to exercise. Complete the summary table as a group. 4
Major Endocrine Glands and Their Hormones
The Endocrine System The endocrine system is responsible for releasing hormones from glands into the circulation. These hormones act on specific receptors to perform a number of functions in the body, including: Regulating cellular metabolism Facilitating the cardiovascular response to exercise Facilitating transport across cell membranes (e.g., insulin) Inducing secretory activity (e.g., ACTH and cortisol) Modulating protein synthesis
Hormonal Response to Exercise Hormones are necessary to help the body make acute and chronic adaptations to exercise. Growth hormone (GH) Secreted by the anterior pituitary gland Facilitates protein synthesis Mediated by insulin-like growth factors Growth hormone, released by the anterior pituitary gland, supports the action of cortisol and plays a role in protein synthesis. Dramatic increase during short-term physical activity
Slow-acting Hormones Cortisol, released by the adrenal cortex, stimulates the mobilization of free fatty acids (FFA) from adipose tissue, mobilizes glucose synthesis in the liver, and decreases the rate of glucose utilization in the cells. Increases with intensity and stress on the body Prolonged elevated levels have been linked to excessive protein breakdown, tissue wasting, negative nitrogen balance, and abdominal obesity. Cortisol promotes protein and triglyceride breakdown to aid in maintaining blood glucose.
Catecholamines Epinephrine and norepinephrine Collectively called the catecholamines Secreted by the adrenal medulla as part of the sympathetic response to exercise Two major roles: Increase cardiac output (increase HR and contractility) Stimulate glycogen breakdown in the liver (glycogenolysis)
Catecholamines Hormones that ensure blood glucose maintenance during exercise and quickly return blood glucose concentrations back to normal after exercise include the catecholamines (epinephrine and norepinephrine). Increase cardiac contractility, leading to increased cardiac output Vasoconstriction of non-working muscles increases total peripheral resistance, causing an increase is systolic blood pressure (SBP) Epinephrine only: Dilates respiratory passages and reduces digestive activity and bladder emptying Stimulates the mobilization of stored carbohydrates and fats, the production and release of glycogen, and glycogenolysis in skeletal muscle Promotes lipolysis Alerts the central nervous system (CNS) of impending stressors
Blood Pressure & Electrolyte Balance Antidiuretic hormone (ADH) Also called vasopressin Secreted by the posterior pituitary gland Reduces urinary excretion of water in response to the dehydrating effects of sweat during exercise Aldosterone Aldosterone limits sodium excretion in urine to maintain electrolyte balance.
Blood Glucose Regulation Insulin and glucagon Secreted by the pancreas (specifically, the islets of Langerhans) Insulin is active when blood glucose levels are high to move glucose from the blood to the tissues. Glucagon is active when blood glucose is low to stimulate glucose release from the liver.
Insulin and Glucagon Activation of the sympathetic system during exercise suppresses the release of insulin from the pancreas. Insulin sensitivity increases, requiring less insulin for the same effect. Glucose uptake by the skeletal muscle occurs at a higher rate. Glucagon, also released from the pancreas, stimulates an almost immediate release of glucose from the liver. Facilitates an increase in blood glucose levels in response to low levels (negative feedback loop) This reaction takes effect as exercise progresses and glycogen stores deplete.
Gender The relative amounts of testosterone (in males) and estrogen (in females) account for specific variances in males and females and their physiological response to exercise. Outside of the hormone-attributed differences, men and women have very similar responses to exercise.
Testosterone & Estrogen Testosterone and estrogen Testosterone (male sex hormone) is secreted by the testes. Responsible for masculine characteristics and muscle-building (anabolic) effects Estrogen (female sex hormone) is secreted by the ovaries. Responsible for feminine characteristics and bone formation and maintenance May play a role in amenorrhea and the female athlete triad
Stress & Hormonal Response Negative changes can occur primarily due to elevated levels of stress hormones such as norepinephrine and cortisol. Cortisol can also cause hunger following stress and encourages storage of visceral fat (belly fat), which is associated with many chronic diseases, such as diabetes, cardiovascular disease and some cancers. Exercise may help decrease stress hormone levels and alleviate these symptoms. Physiological system Musculoskeletal system Cardiovascular system Immune system CNS Gastrointestinal system Effects of stress Tension headache, neck and shoulder discomfort, and back pain Premature coronary artery disease (CAD), hypertension, increased platelet adhesiveness, and heart attack Suppression of T-cell function, increased vulnerability to infections, and viral illnesses Impaired memory and neural degeneration Stomach ache, nausea, constipation, and diarrhea 16
Hormonal Changes Generally, the hormonal response to a given exercise load declines with regular endurance training. Resistance-training adaptations result in increases in growth hormone and testosterone (especially in men), which are associated with strength improvement.
Summary In response to exercise, a series of physiological adaptations (acute and chronic) occur specific to the encountered stress. This chapter covered: The hormonal response to exercise