Issue #45: The Hormone Issue

There is no doubt that regular exercise has a long list of benefits. People who regularly exercise are healthier, stronger, more confident, and overall happier people.1 While some of these changes might be obvious, such as feeling and looking stronger, clothes fitting loosely, and having more energy, the processes that cause these changes are not noticeable. They happen deep within the cells of your body, and are driven by hormones that are released as a result of physical activity.

Young woman lying on the yoga mat and doing fitness exercise at gym

Hormones are substances that circulate through the body to stimulate activity in the body’s cells. They are produced by the endocrine system, and act as messengers to control most of your body’s major functions.2 There are eight hormones that are involved with exercise, and each plays a different role in how you respond to physical activity. In this article we will cover the first four hormones responsible for your body’s changes. For each hormone covered, a basic description of the hormone, as well as training-specific changes you can make to maximize your hormonal potential, will be included.


Insulin is a hormone released by the pancreas, and helps the body use glucose for energy.3,4 In other words, insulin acts as to put glucose (sugar) from the bloodstream into the cells to be used for energy.  Type 1 diabetes results when the body doesn’t produce sufficient amounts of insulin, preventing glucose from effectively getting into the cells. With type 1 diabetes an individual has all the glucose the body needs, but doesn’t have the key to open the cells. In type 2 diabetes (insulin resistance) the body produces enough insulin, but no longer responds to it. To continue the metaphor, your body may have the keys to put the energy into the cells, but all of the locks have been changed. If the cells cannot appropriately absorb glucose from the bloodstream, the body will get its energy elsewhere, which can result in a dangerous condition known as ketoacidosis.5 Regular exercise has been shown to increase insulin sensitivity, ensuring that your locks and keys are always working, and your body is able to effectively pull energy from the circulating glucose.6,7,8,9

Insulin Dictionary Definition closeup black and white

What you need to know to improve your training

If fat loss is your goal, make sure to consume lower amounts of carbs immediately before your workout to ensure low levels of insulin release during exercise. This will allow you to metabolize more fat during your workouts.10,11 However, if you’re looking for maximum performance output (i.e. heavy weight lifting or short, high-intensity interval workouts), then you will want to ingest carbohydrates immediately pre-workout to provide increased energy levels.12,13 Although the specific amount of pre-workout carbohydrate intake varies, research suggests that about 50g of carbohydrates pre-workout is sufficient.14



Cortisol is a steroid hormone released by the adrenal gland. It is responsible for a variety of bodily functions in response to physical stress, including: mediating metabolic function (the breakdown of protein and fat as a fuel source), suppressing the immune system, and helping to control blood pressure and blood sugar levels, to name a few.15,16 Cortisol levels naturally increase during exercise16, and ensure proper glucose availability by converting fat and protein stores into usable energy.15 While an elevation in cortisol levels is natural (and necessary), chronically elevated levels of cortisol can have negative effects on the body, including: inhibited insulin production17, increased visceral fat storage (fat stored around the organs, which can lead to an increased risk of cardiovascular disease)17,18,19 and increased appetite.20,21

growth hormone written on notebook. Test tubes and hormones list

What you need to know to improve your training

Elevated cortisol levels are natural during strenuous exercise, but chronically elevated levels can lead to negative consequences. There are steps you can take to lower your cortisol levels. First, add in some low-intensity exercise to your program. Aerobic exercise at no more than 40% of your maximum heart rate has been shown to decrease resting cortisol levels.22 Second, make sure you are getting enough sleep every night. Studies show that cortisol levels drop during sleep, regardless of the time of day.23 Experts suggest aiming for seven or more hours of sleep each night.24 Additionally, nutrition plays an important role in cortisol levels. Inadequate calorie and protein consumption have been found to increase cortisol secretion.25,26 Make sure you are consuming enough calories (avoid very low-calorie diets) and protein, daily.



Epinephrine (adrenaline) is a catecholamine released in response to acute stress, and is responsible for your body’s “fight-or-flight” response. It has a variety of effects on the body, including: increasing heart rate and blood output, as well as mobilizing glucose (stored as glycogen in the liver) and fatty acids which can be used for energy.27,28 A greater release of epinephrine has also been shown to improve force output during resistance training sessions.31 Additionally, the release of epinephrine as a result of physical activity has been found to increase the activity of Natural Killer (NK) cells—cells responsible for binding to tumor- and virus-infected cells to destroy them.29 The release of epinephrine in response to physical stress also plays a role in improved memory retention.30

Tired exhausted man runner sweating after cardio workout. Running male adult taking a break and breaking a sweat after a run under the sun. Fitness athlete breathing heavily from heat exhaustion.

What you need to know to improve your training

Greater levels of epinephrine are released as a result of short duration, high-intensity exercise.31 Participating in a resistance training program that includes lifting at one’s 10 repetition maximum (complete failure on the 11th rep), with 10-60sec rests between sets, has been shown to increase catecholamine levels, including epinephrine.32 Additionally, individuals who regularly participate in heavy resistance training programs produce greater levels of epinephrine release in response to exercise.33 Although lifting weights at your 10-rep max with short rest periods is sufficient to increase epinephrine release, it is important to vary your workouts (both type and intensity). Prolonged activation of the adrenal gland as a result of acute physical stress has been shown to increase cortisol levels (which, as we’ve seen above, is no good).34


Brain-Derived Neurotrophic Factor (BDNF)

Although not technically a hormone, this protein is responsible for the growth, maturation, and maintenance of nerve cells.35 The increase in BDNF levels as a result of exercise could be the main reason for its brain-boosting benefits, including improvements in learning and memory.36,38 Additionally, increased BDNF levels can help combat normal brain degeneration that occurs as a result of aging.37,38

scatterbrained man

What you need to know to improve your training

Aerobic exercise (cardio) produces greater increases in BDNF levels than strength training39, although more research needs to be done. Additionally, the beneficial effects of aerobic exercise on BDNF levels is intensity-dependent.40 Research shows that moderate, long-duration aerobic exercise completed at roughly 50-70% of maximum heart rate for 20-40 minutes produces the greatest increase in BDNF levels.41,42,42 However, acute changes in BDNF levels are minimal compared to the benefits that come from consistent participation in aerobic activities.43

Each of these hormones plays a significant role in your body’s adaptation to the physical stress and performance of exercise. One important thing to consider is the importance of including a variety of activities in your exercise program (i.e. heavy strength training, as well as both moderate and high intensity cardio) to ensure you are reaping the most benefits. In part two of this article, we will cover the remaining hormones that play a role in exercise: testosterone, growth hormone, glucagon, and insulin-like growth factor.

About Alex McBrairty

Alex McBrairty is a personal trainer based in Ann Arbor, MI. He educates his clients in exercise, nutrition, and behavior change to help them develop new habits and reach their goals. Alex also teaches, writes, and speaks about fitness motivation and behavior change.