Cortisol and Exercise: The Truth, Not the Myth

Let’s start by laying the foundation first. What exactly is cortisol? Why do we need it? What does it actually do?

As you can imagine the answers to these questions can be extremely complicated so I will do my best to keep it as simple as possible while maintaining accuracy.

Cortisol is a hormone made in, and released by, the adrenal glands. Just like all hormones, it is a chemical messenger that instructs cells in the body to perform specific tasks. A cool thing about hormonal cell signaling (yes, I think it’s cool; no, I don’t get out much) is that the same hormone can be responsible for several different tasks because each cell responds differently to each hormone. Cortisol, as an example, tells fat cells to break down large stored fatty acids into smaller, more usable ones. It tells liver and muscle cells to break down glycogen (the big storage form of glucose) into individual units of glucose. It also tells muscle cells to break down certain protein molecules into specific amino acids and then instructs other liver cells to turn those amino acids into glucose. Why does this all happen? One simple reason, energy mobilization. Boiled down into a single sentence; cortisol’s job is to create and mobilize as much fuel as possible.

Evolutionarily this is the hormone responsible for giving you the energy you need to “run from the dinosaur” which is why cortisol is considered a fight or flight hormone but that’s also why cortisol gets a bad rap. Somewhere along the way, cortisol was turned into a villain - especially in content aimed at women. The message usually sounds like this: high intensity exercise spikes cortisol, cortisol causes belly fat, so women should avoid intense exercise if they want to look skinny. It’s a logical thought progression because those first two statements can be 100% true. It does a great job of capturing your attention and though those things are true, it’s missing very important context, without which, misleads people to false conclusions. Cortisol is not an evil thing that needs to be avoided. It is not a toxin that needs to be cleansed. It is not a sign that your body is malfunctioning. In fact, it’s the opposite. It means your body is functioning normally, the way it is supposed to. Cortisol is a necessary hormone that helps regulate metabolism, immune activity, cardiovascular tone, and the bodies stress response. Your body uses it every day to maintain stability, not to sabotage you.

Under normal conditions, cortisol is released in a daily cycle, with higher levels in the morning and lower levels later in the day. Which makes perfect sense; you need extra energy to wake up, you don’t need extra energy to fall asleep. That’s considered your baseline level of cortisol. We can also get an extra boost of cortisol when we need extra support - like during illness, fasting, psychological stress, and exercise. When you need energy the most, cortisol is there to make sure you have it. We have a normal baseline that follows a cycle and the ability to release a little more when we need a little more. Also important to note that it doesn’t last forever. When cortisol is released into your blood stream it has a half life of about 1 hour. That means after 1 hour, half of it is either metabolized or otherwise inactive. After another hour, half of half is metabolized or inactive (so 25% of the original amount), and so on. So we can clearly see that within a few hours, serum levels are back to baseline and unless that window directly interferes with your bedtime, it doesn’t cause a dysregulation in your daily rhythm. In fact a 2022 systematic review found that although a single bout of exercise increases cortisol levels (as it should), a regular pattern of exercise actually reduces your baseline cortisol levels, demonstrating that the body adapts to physical stress in a productive way.

Now for the most important part.

This is the part the myth gets wrong: a temporary cortisol rise from exercise is not the same thing as chronic cortisol dysregulation. In fact, regular training often looks more like adaptation than damage. The same review describes a more moderate cortisol response in trained individuals consistent with adaptation to repeated exercise stress. That means the more you incur an exercise induced cortisol event, the less impact it has overall. Pair this with another study that found that exercise intensity dampened the cortisol response to a later psychosocial stressor in a dose-dependent fashion, which suggests training can improve stress resilience rather than “burn out” the system. A broader systematic review and meta-analysis also found that physical activity overall was associated with better sleep. The science is consistent on this issue and has been for quite some time.

What little truth does the myth lean on to gain traction? Someone under deep chronic psychological stress is getting frequently repeated doses of cortisol multiple times per day, multiple days per week, etc. The body never gets a chance to return to baseline before it gets ramped up again. There are several colorful names given to this condition and it can present in a myriad of symptoms but this doesn’t support the vilification of exercise, it arguably reinforces the importance of it. This is why when researchers actually test higher-intensity training the results do not support the fear-based narrative. In one study of older postmenopausal women, eight weeks of supervised high-intensity cycle training increased VO₂ max by 18%, improved cardiovascular risk profile, and was well tolerated. A 2024 systematic review concluded that aerobic training may improve cardiometabolic health in postmenopausal women. A meta-analysis with women also found that HIIT exercise reduced body weight and abdominal fat overall. These findings are a far cry from “HIIT is bad for women’s hormones.”

The more honest message is this: women do not need to fear cortisol. They need to respect total stress load. A well-programmed dose of HIIT can be useful, effective, and appropriate. A poorly recovered, under-fueled, all-gas-no-brakes approach can be a bad idea - but that is a programming problem, not proof that women are too hormonally fragile for exercise intensity. The right question is not whether HIIT raises cortisol. Of course it does, and it needs to. The right question is whether the overall training plan helps you adapt, recover, and feel stronger, fitter, and more resilient over time. The evidence points to yes, especially when intensity is dosed intelligently and balanced with recovery.

Now that we know what the problem is, let’s talk about solutions. For the sake of not offering clinical recommendations for treatment of mental health conditions let’s stick with general advice. Try identifying and eliminating sources of stress. If cortisol is released in response to stress, the best line of defense would be not subjecting yourself to stress in the first place. Easier said than done, however when we consider that stress is not so much the things going on around us as much as it is the reaction we have to those things, it might help to put yourself back in the drivers seat . Some people were born with higher stress sensitivity than others, but calm under pressure is a learned behavior at any age. As we’ve learned before, getting more regular intense exercise helps your body buffer itself against stress. Another pro tip is working with a coach to structure your workouts or program to ensure you are recovering properly.

Bottom line: cortisol is not the enemy, and HIIT is not automatically harmful for women. Cortisol helps you wake up, regulate inflammation, maintain blood pressure, and mobilize fuel for demanding situations, including exercise. A short-lived rise during hard training is part of the adaptation process, not a sign that your body is broken. Women do not need blanket rules built on hormonal fearmongering. They need better coaching, better recovery, and better context.