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FACT CHECKEDDid 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.
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:
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:
Cortisol is produced by the adrenal glands and secreted during times of stress. Some occasions which cause an increase in cortisol include:
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:
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:
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.
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.
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.
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.
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.
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:
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:
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.
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:
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.
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:
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.
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:
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.
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.
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:
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Garett Reid
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