Written by Garett Reid | NSCA, CSCS, CISSN, M.S.E.S.S
Fact checked by Sam Coleman, Co-Founder
FACT CHECKED
Did you know that exercise increases cortisol levels? How could that be as many speak about cortisol as if it’s the worst thing ever! Does this mean you should stop training? That's obviously a ridiculous statement, but some might come to that conclusion from the way people speak about this essential hormone. Now, there is truth that constantly elevated cortisol can hurt your gains but there’s also a lot of confusion. This article is going to tell you the truth about cortisol and how it affects your training.
What Is Cortisol?
Let's start this article by explaining what cortisol is.
First off, cortisol is a steroid. Yep, cortisol belongs to a group of steroid hormones known as "glucocorticoids” and we know what you're thinking. The term "steroid" is largely misused among the general public as it technically refers to any organic compound that includes a specific arrangement of four fused carbon rings. These compounds are then broken down into 2 groups:
- Corticosteroids
- Sex Steroids
The steroids most people think about belong to the sex steroids, with the most obvious being testosterone and its synthetic versions. However, cortisol belongs to the other group, corticosteroids which include glucocorticoids. Some characteristics include:
- Metabolism: Glucocorticoids help regulate carbohydrate, fat, and protein metabolism by promoting gluconeogenesis to increase blood glucose levels.
- Immune Response: They have anti-inflammatory and immunosuppressive effects, helping to modulate the immune system and reduce inflammation.
- Stress Response: Glucocorticoids are released in response to stress, helping the body manage and adapt to stressors.
- Blood Pressure Regulation: They can influence blood vessel function and fluid balance, contributing to blood pressure regulation.
Cortisol is produced by the adrenal glands and secreted during times of stress. Some occasions which cause an increase in cortisol include:
- Viral infections by activating the HPA axis through cytokines.
- Intense or prolonged aerobic exercise
- Severe trauma or stress can lead to prolonged elevations in blood cortisol.
- Low-carbohydrate diets in an attempt to increase blood glucose levels.
- Increased levels of ghrelin, the hunger hormone.
- High-stress environments
What Does Cortisol Do?
Cortisol's primary role is to create a favorable environment during stressful times and fight-or-flight response. One of its main objectives is to elevate blood glucose levels to provide energy for the muscles and the brain. It does this through several mechanisms:
- Promotes gluconeogenesis, which is the biosynthesis of glucose from certain non-carbohydrate carbon substrates such as protein
- Promotes glycogenolysis, which is the breakdown of glycogen in the muscle
- Decreases insulin sensitivity of the muscle to reduce the uptake of glucose into the muscle
- Increases glucagon, a hormone that prevents blood sugar from dropping
- Increases lipolysis, which is the breakdown of fat into fatty acids to be used for fuel
- Decreases protein synthesis, which reduces the need for energy while also freeing up amino acids to be used in gluconeogenesis
All of these processes work together to provide a surplus of energy for your body to use during stressful times.
In addition, it plays several other roles, such as:
- Suppresses inflammation
- Manages blood pressure
- Helps manage your sleep cycle
When Is Cortisol Highest?
It's important to realize that cortisol levels fluctuate throughout the day, in line with your circadian rhythm. Cortisol levels are highest in the morning and lowest before you sleep. This is important to realize if you ever did have your levels tested. Further, you should get multiple tests on several days at the same time to get a better estimate as again, levels can fluctuate on the hour.
Effects Of Prolonged Elevated Cortisol
Our bodies are smart, so nothing they do is inherently harmful; everything has a purpose aimed at survival. We can also apply this to cortisol which is useful during times of stress to help the body manage and escape the situation.
The problem is that the original design assumed these stressful times would come and go.
While we can't say for sure what was going on, it's safe to say that our ancestors didn't have mortgages, exams, social media drama, or taxes to worry about. Rather, they hung out and enjoyed themselves until a bear wandered into their territory or they had to hunt down food.
Unfortunately, our modern world is full of stressors. Some studies have found that students can see a 9-fold increase in cortisol levels during exams¹! In other words, our lives are full of stress, and we know that this has a profound effect on our bodies.
Numerous harmful effects of prolonged cortisol exist, such as increased physical and mental fatigue. Another major factor is immunosuppression, which leads to various health complications. However, the one we're most concerned about is how, or if, it can affect body composition.
Does Cortisol Cause Weight Gain?
As mentioned above, cortisol's primary function is to keep blood sugar levels high. This can help temporarily, but when cortisol is constantly high, it can have deleterious effects.
One of the major concerns is that your body can eventually become permanently resistant to insulin which can eventually lead to gaining excessive weight and developing type II diabetes.
Another aspect that worries bodybuilders is that perpetually high cortisol levels can lead to muscle loss. Remember that it can increase gluconeogenesis, which converts non-carbohydrate sources, like amino acids, into glucose.
The problem is that when there are no free amino acids, your body could promote a process known as proteolysis², which is when your muscle breaks down to free up amino acids. With that said, this does not happen easily. You must train for a couple hours with poor nutrition on a regular basis to see significant drops in muscle mass.
However, this is what the major concern is with prolonged endurance training or excessive caloric deficits and training.
Does Exercise Increase Cortisol?
Some cortisol is good, while too much is bad so we now want to look at the effect of exercise on cortisol and see where it sits on the scale.
As we mentioned, cortisol does see an increase during some forms of exercise. This is dependent on the type of exercise and the intensity being performed.
Type Of Exercise And Cortisol
Not all forms of exercise increase cortisol. For example, it's been shown that 10 sets of 5 reps use speed squats causes no increase in cortisol while increasing testosterone at the same time³.
One area we know increases cortisol is endurance training. Remember that cortisol's primary job is to maintain high blood sugar levels, which is especially needed during endurance training. However, what's important to realize is that during recovery, the body switches and can become anabolic with low cortisol and high testosterone⁴.
Raises are not permanent and will come down after your training. This is another reason why an acute rise is not something to worry about.
Many ask how long they can run until they experience a marked increase. This is very hard to say due to all the variables. Basically, it's a result of duration and intensity. For example, a general rule of "no more than 90 minutes" is given for low-moderate intensity. However, running a fast 5k will cause significant increases that remain until bedtime⁵.
A large factor is the amount of energy your body needs and the amount of carbs that are available. Times when more glucose is needed, your body will see higher cortisol and vice versa. With that said, the general rule-of-thumb is that exercise of higher intensity produces greater acute cortisol levels⁶.
Exercise, Nutrition & Cortisol
A famous 2006 study examined the effects of exercise on cortisol in four groups of untrained men over the course of 12 weeks⁷. This is important because, as we need to primarily focus on the sum game rather than the acute mechanistic effects of one occurrence. As these men trained for 12 weeks, we'll be able to see how any changes cause long-term effects as well as the effect of food.
Now specifically, the researchers were looking at how nutritional interventions affected cortisol. The 4 groups of men ingested one of the following drinks during their training:
- 6% Carb solution
- 6 g EAA mixture
- Combined CHO + EAA supplement
- Placebo (Water)
The men followed the same resistance training program twice weekly, each session taking about 60 minutes.
Here's how cortisol was affected 30 minutes after a single session:
- Water- Increased 54%
- EAA- No change
- Carb- Decreased 23%
- Carb + EAA- Decreased 27%
As we can see, there was a large difference when drinking just water or ingesting carbs. This is likely because ingesting carbs provided plenty of glucose, so cortisol wasn't needed.
So now, let's look at how this affected muscle gain and fat loss.
- Water- Lost 3.3lbs of fat // Gained 3.9lbs of muscle
- EAA- No change Lost 2.9lbs of fat // Gained 6.4lbs of muscle
- Carb-Only- Lost 2.8lbs of fat // Gained 6.4lbs of muscle
- Carb + EAA- Lost 4.4lbs of muscle // Gained 8.7lbs of muscle
Wow. This study does show that the nutritional intervention caused some significant changes. While we might first say, "Aha, cortisol!", the numbers don't directly correspond.
Some instances include:
- The water group lost more fat than EAA and carbs.
- EAA had no change in cortisol, while Carb-Only had a significant decrease. However, they gained the same amount of muscle.
- Carb-Only and Carb + EAA had similar drops in cortisol, yet the Carb + EAA had 58% more fat loss and about 36% more muscle gain compared to Carb only.
We should also remember that they were training fasted, so these changes are more likely due to muscle protein breakdown and lower muscle protein synthesis. However, the water only still gained muscle, showing that cortisol isn't going to eat your muscle!
Another important factor is this occurred over 12 weeks so neglecting your nutrition on a constant basis could produce meaningful effects. However, messing up here and there isn’t going to break you.
Can Cortisol Help Build Muscle?
Just to really throw a wrench in this issue look at this study from 2012⁸. We'll get right to it; a large group of men followed a 12-week resistance training program. Throughout the training, researchers measured various hormones, including:
- Cortisol
- Testosterone
- HGH
- Serum growth hormone
- Insulin-like growth factor
At the end of the study, the men with higher cortisol readings had slightly greater muscle gain! Even crazier, testosterone levels had no correlation! Now, we're not sure what to make of this. However, we do know our body is complex and is designed to strive. We can’t isolate single responses and draw a conclusion from it. This principle can apply to just about everything in fitness and nutrition.
How To Keep Cortisol Low When Exercising?
After looking at it, we see that cortisol and exercise are anything but straightforward and likely don't even matter in the long run assuming you follow some basic guidelines. Like, you would have to continuously follow a really poor plan or try to see some of the horror stories you hear.
With that said, there are some general guidelines if you want to keep your cortisol levels low:
- Don't train fasted. If you do, consume nutrition shortly after training.
- Consume carbs during your training.
- Aim to keep training around 60-90 minutes. This can vary depending on exercise type and intensity as well as nutrition.
And again, we are not saying if you train fasted or don’t eat carbs your muscle will waste away. We’re simply saying if you want to keep your cortisol levels low.
Can Chronic Exercise Decrease Cortisol?
Yes.
Here’s the real deal. While exercise can increase cortisol acutely, unless you plan on only training once, this isn’t going to be an issue. In fact, if you have a stressful life, chronic exercise can actually decrease cortisol!
In fact, it seems that more training is better! A large meta showed that training 5 times a week had a “very large effect” on decreasing cortisol levels⁹. On the other hand, training three times a week had a “moderate effect”. Either way, training is going to improve your resting cortisol levels in the long run.
The Final Say On Cortisol
We can sum up cortisol's relationship with exercise as this: Don't be scared of your body's natural processes. If you start trying to optimize every single physiological mechanism in your body, you're going to go crazy.
Don't believe us? Well, did you know that resistance training increases muscle protein breakdown¹⁰!?
So maybe we should stop training?! Of course not as it also increases muscle protein synthesis to a higher degree! The point is many processes are occurring simultaneously, and we are more worried about the end sum.
With that in mind, assuming you're involved in a normal amount of training and eating properly, cortisol from exercise isn't an issue you should even worry about. In fact, if you're training so much that cortisol becomes a problem, that tells us you're doing something you shouldn't!
Considering all that, you should be more concerned with the overall decrease in cortisol in your life that can occur from regular exercise.
References:
- Çay, M. (2018). The Effect of Cortisol Level Increasing Due to Stress in Healthy Young Individuals on Dynamic and Static Balance Scores. Northern Clinics of Istanbul, 5(4). https://doi.org/10.14744/nci.2017.42103
- Braun, T. P., & Marks, D. L. (2015). The regulation of muscle mass by endogenous glucocorticoids. Frontiers in Physiology, 6. https://doi.org/10.3389/fphys.2015.00012
- Fry, A. C., & Lohnes, C. A. (2010). Acute testosterone and cortisol responses to high power resistance exercise. Human Physiology, 36(4), 457–461. https://doi.org/10.1134/s0362119710040110
- Caplin, A., Chen, F. S., Beauchamp, M. R., & Puterman, E. (2021). The effects of exercise intensity on the cortisol response to a subsequent acute psychosocial stressor. Psychoneuroendocrinology, 131, 105336. https://doi.org/10.1016/j.psyneuen.2021.105336
- Administrator. (2017, June 20). Short, high-intensity running substantially stresses the body. Liu.se; Linköping University. https://liu.se/en/article/kort-och-snabb-loptur-stressar-kroppen-ordentligt
- Hill, E. E., Zack, E., Battaglini, C., Viru, M., Viru, A., & Hackney, A. C. (2008). Exercise and circulating cortisol levels: the intensity threshold effect. Journal of Endocrinological Investigation, 31(7), 587–591. https://doi.org/10.1007/BF03345606
- Bird, S. P., Tarpenning, K. M., & Marino, F. E. (2006). Independent and combined effects of liquid carbohydrate/essential amino acid ingestion on hormonal and muscular adaptations following resistance training in untrained men. European Journal of Applied Physiology, 97(2), 225–238. https://doi.org/10.1007/s00421-005-0127-z
- West, D. W. D., & Phillips, S. M. (2011). Associations of exercise-induced hormone profiles and gains in strength and hypertrophy in a large cohort after weight training. European Journal of Applied Physiology, 112(7), 2693–2702. https://doi.org/10.1007/s00421-011-2246-z
- Beserra, A. H. N., Kameda, P., Deslandes, A. C., Schuch, F. B., Laks, J., & Moraes, H. S. de. (2018). Can physical exercise modulate cortisol level in subjects with depression? A systematic review and meta-analysis. Trends in Psychiatry and Psychotherapy, 40(4), 360–368. https://doi.org/10.1590/2237-6089-2017-0155
- Tipton, K. D., Hamilton, D. L., & Gallagher, I. J. (2018). Assessing the Role of Muscle Protein Breakdown in Response to Nutrition and Exercise in Humans. Sports Medicine, 48(1), 53–64. https://doi.org/10.1007/s40279-017-0845-5
Garett Reid
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