Edited by Kate Findley and proofread by Angela Shoemaker, The Great Courses Daily
Do you need to flee from a wild animal? Do you need to melt away the flab around your abs? Two hormones work together to make either one happen! Professor Ormsbee explains.
Catecholamines and Fight-or-Flight Response
Cortisol is commonly known as the stress hormone, but in response to stress, exercise, or a frightening situation, many other hormones can also be released. Two of these hormones are called the catecholamines, and they are important contributors to body composition changes.
Imagine that you are taking a walk through the woods and a bear jumps in front of you. In this situation, your body immediately and automatically prepares you to deal with the situation as best it can. We refer to this as the fight-or-flight response. During this situation, two hormones called epinephrine and norepinephrine will be secreted in high amounts into the bloodstream.
These hormones are produced in the adrenal glands, which are positioned on top of each kidney. The adrenal gland is composed of an outer layer called the cortex and an inner layer called the medulla. The epinephrine and norepinephrine are produced from the amino acid tyrosine in the medulla of the adrenal glands. Additionally, norepinephrine can also be produced directly from sympathetic nerve endings, throughout your body.
Together, epinephrine and norepinephrine are called the catecholamines. They immediately provide glucose for your body by breaking down stored glycogen and stored fat, releasing it to your muscles, so that you can either fight or run away.
Breaking Down Fat
These same responses will occur when you begin to ramp up the intensity of exercise. During intense exercise, catecholamines are released and you will notice that your heart rate and respiratory rate increase, improving blood flow and delivering oxygen to organs and tissues. Again, this happens to allow you to have a better fight-or-flight response.
Also, catecholamines begin to mobilize or break down stored body fat when they interact with receptors that respond specifically to the catecholamines, called adrenergic receptors, or adrenoceptors.
Since exercise and catecholamines both lead to lipolysis, or fat breakdown, it is easy to see why exercise can be effective for burning fat as a fuel for the body to use. If you simply exercise regularly, you take advantage of the catecholamine response that occurs.
For example, a long, slow training session would likely have the lowest catecholamine response; however, if you work out intensely with enough fuel to go all-out, but not too much that you stop lipolysis, you may have a great recipe for fat burning. This is in part because you have elevated your catecholamines the most with this type of intense workout.
This is a trial-and-error process: You have to experiment with your food intake and the intensity of your workouts to adjust accordingly to gain optimal fat loss. Keep in mind, that if you exercise at high-intensity levels, you will also be able to burn calories for a duration of time following the end of the workout session. This after-burn effect can last from just a few minutes to 24 hours, depending on the level of exercise intensity.
Thyroid and Metabolism
Like other hormones, the thyroid hormones also have a powerful influence on metabolism, body composition, and health. They may be the most misunderstood hormones when it comes to body composition.
How many people have blamed their weight gain on a faulty thyroid hormone? “I have heard this dozens of times, but the truth is that while thyroid problems can certainly contribute to weight gain, or even weight loss, the situations where this is the primary reason for weight change are pretty rare, particularly when considering the excellent advances in medications for diagnosed thyroid problems,” Professor Ormsbee said.
We’ll delve more into the thyroid and the connection between weight gain and weight loss in tomorrow’s article.
Michael Ormsbee is an Associate Professor in the Department of Nutrition, Food, and Exercise Sciences and Interim Director of the Institute of Sports Sciences and Medicine in the College of Human Sciences at Florida State University. He received his MS in Exercise Physiology from South Dakota State University and his PhD in Bioenergetics from East Carolina University.