You don't need to be suddenly frightened or faced with danger to get a rush of adrenalin, says a Brigham Young University professor of physiology and anatomy.
"The adrenal gland actually has a much more mundane - but equally important - responsibility," said Professor William W. Winder, who for 10 years has conducted research on the pivotal role of the liver, adrenal gland and stress hormones during exercise.Winder recently presented research results giving new insights into the functions of adrenalin at the annual meeting of the American College of Sports Medicine. His project is being funded by a grant from the National Institutes of Health.
Working with genetically similar albino rats, Winder and his laboratory crew have shown that epinephrine (also known as adrenalin) sharply rises when the liver's supply of glycogen - the body's primary source of energy - is depleted.
Glycogen is a starchlike carbohydrate stored in the liver and other tissues. When the body needs energy, glycogen breaks down into glucose (or sugar) and is released into the blood stream, raising blood sugar levels and providing a source of energy.
Winder said that as soon as an exercising individual runs out of liver glycogen, the body must rely on synthesis of glucose from lactic acid or amino acids, which are derived from the muscles. Energy also can be derived from fatty acids.
"This method of creating energy, from the muscles instead of the liver, takes the body considerably more time," Winder said, "and it tends to open the door for blood sugar levels to drop."
Low blood sugar is commonly known as hypoglycemia.
People suffering from hypoglycemia have chronic low blood sugar, headaches and depressed energy levels. It is potentially a serious health problem and can become permanent if not identified and treated.
Winder said usually when blood sugar levels drop, people get tired enough to stop exercising or expending energy. But for some people, such as marathoners or those in any sport where exercise is sustained at a high level for several hours, hypoglycemia may be a problem.
Eating a high-carbohydrate meal several hours before a race or any prolonged exercise would be a good idea, he said.
Importantly, the body's signal to seek energy from sources other than the liver comes from a healthy dose of adrenaline, Winder said.
"Epinephrine is a signal to the muscles, particularly to those muscles that aren't working, to draw out glycogen for the body's use when the body is working to its limit," Winder said. "Increasing the concentration of epinephrine in the blood stimulates production of lactic acid from resting muscles."
The harder a person exercises, the more glucose the body needs and the quicker the liver's stored glucose runs out.
"Maintaining blood glucose levels is a very important job assigned to the liver," he said. "The brain has an absolute requirement for glucose. People with marginal hypoglycemia, for instance, may notice neurological problems such as flickering blind spots and headaches. That's because the brain isn't getting enough glucose for its needs."
The best advice, then, for anyone involved in competitive sports that require a sustained level of exercise is to avoid prolonged fasting before a race, said Winder.
Anyone with an impaired or absent adrenal gland, because of disease or surgery, is also at risk for hypoglycemia because of the body's inability to produce adrenaline.
"These people should be careful about exercising after a fast or should be sure to eat a few hours before any prolonged exercise," Winder said.
Long-term, type-one diabetics, who take daily insulin shots, should also watch their diet when exercising.