“I’m an Exercise Physiologist—Here’s Why You Shouldn’t Worry About Cortisol Spikes When You Do HIIT Workouts.” 

Most of us are pretty stressed out these days. We stress over money, work, the news, and we stress over…stress. As if that wasn’t enough, lately we’re hearing more about how our workouts might exacerbate our stress. All over TikTok and Instagram, you’ll find fitfluencers warning that high-intensity cardio workouts spike our cortisol, aka “the stress hormone.” With posts racking up hundreds of thousands of likes and saves, the thought of making our stress worse—by doing something healthy—has clearly struck a nerve. 

But is there any truth to these claims? Well, the reality is that it depends. Like most things on social media, there’s a good deal of nuance that gets lost. Here’s what experts want you to know before you swear off HIIT class for good. 

What is cortisol and what does it do? 

Cortisol is most commonly known as the stress hormone. Our adrenal glands release it whenever our brain perceives a threat—whether that’s physical or mental. This causes a cascade of changes designed to help us handle that extra stress. “It increases blood sugar, enhances the brain's use of glucose, and increases the availability of substances that repair tissues,” says exercise physiologist Rachelle Reed, Phd, ACSM-EP. 

But cortisol actually does a lot more than simply turn on this fight-or-flight response. It plays a role in helping us fight infections, maintaining our blood pressure, regulating blood sugar levels, suppressing inflammation, and more. “Cortisol is a critical hormone,” says Susan Sotir, PhD, a triathlon coach and certified strength and conditioning specialist. “We need to have it to function as humans.” 

Does exercise increase cortisol? 

A tough workout is one of many stressors that will trigger a release of cortisol. Whenever you hit a certain intensity or duration that challenges your current fitness, the levels of this hormone will rise. “Your body needs to meet the demand of the stressor, so it's going to secrete more cortisol,” says Reed. 

But here’s what many TikTok videos leave out: Since exercise only stresses us for a short period, your cortisol levels return to baseline fairly quickly after you cool down. 

More importantly, a meta-analysis from 2022 found that regular physical activity can improve our cortisol regulation, actually decreasing levels overall. (That could partially be because exercise can improve our sleep, which has a major impact on our cortisol, says Reed.)

So sure, you’re going to see a cortisol spike when you look at a single workout on its own. But when you consider the overall picture painted by all those workouts put together, you see a hormone that’s better regulated in your day-to-day life. 

Can too much cortisol be a problem? 

The danger with cortisol comes when we’re under chronic stress, and instead of simply spiking then coming back down, it stays high. “That’s when things become dysregulated,” says Reed. 

You’ll typically notice fatigue, weakness, and either increased hunger or a lack of it. “You feel ‘beat up’ for lack of a better phrase,” says Sotir. 

If you linger in this state long-term, chronically high cortisol can lead to health problems like heart disease, impaired immune function, type II diabetes, mood disorders (like depression and anxiety), digestive issues, and more. 

Before you start stressing, the good news is doctors can effectively test our cortisol levels to determine whether they’re actually behind any symptoms we’re experiencing. You’ll just want to keep timing in mind when you test: A healthy cortisol response is naturally highest in the morning, and during the follicular phase of our menstrual cycle.  

How to adjust your workouts if your cortisol is chronically high

Our bodies are designed to experience an ebb and flow of cortisol levels. But if they never go down—either because of extreme stress, a cortisol disorder like Cushing’s syndrome, or certain medications that elevate it—that’s when you might reconsider your approach to fitness. 

“If you're under duress all the time, perhaps engaging in a really stressful form of exercise is not your best option,” says Sotir. 

The key there is not to stop exercising altogether. Because remember, with the right approach, staying active can reduce your stress levels. 

Well-designed low-cortisol workouts are both low impact and low intensity. “They’re less likely to release a large amount of cortisol because they're not as stressful to your system,” says Reed. This can include yoga, walking, a low-key Pilates session, tai chi, slow strength training, or gentle swimming. Really, almost any workout with controlled movements where you can keep your breathing smooth and steady can qualify. “Focus on activities that are enjoyable and relaxing.”

Remember: Changing your fitness routine alone won’t solve the problem. If you are diagnosed with high cortisol, Reed says most physicians will also prescribe medication and other lifestyle changes (like improving your sleeping habits).  

For most, a mix of high- and low-cortisol workouts is best

Even though the cortisol spike we get from hard workouts isn’t necessarily a bad thing, it’s not something we want every single day. 

“When we're exercising, we are stressing all of our systems,” says Reed. “Not only your endocrine system—which is helping with cortisol regulation—but also your cardiorespiratory system and musculoskeletal system.” Training hard enough to spike that cortisol means you’re also putting major stress on your heart and lungs, and muscles and joints, which is only healthy as long as you keep it in moderation. 

The key is finding a balance. The general exercise science rule is to do about 20 percent of our workouts at a high intensity (where our rate of perceived exertion hits about seven or higher on a scale of zero to 10). The remaining 80 percent should be done at a moderate effort (more like a four to six out of 10). 

In reality, the vast majority of us don’t get enough exercise. And if you don’t have an actual cortisol problem, doing even less activity could unintentionally backfire and leave you with higher levels in the long run.

“Very few people are doing so much exercise that they need to scale back and do only low-impact, low-intensity work,” says Reed. “Unless you’re diagnosed with an actual disorder, it's good to be aware of, but probably not something you should be hyper-focused on.”