Written by: Kyle Riley BSc (hons) Ex Science
Therapy Co-Founder
You may have heard that doing a tough workout will send your body into “fight-or-flight,” spiking cortisol, causing weight gain or burnout. Recently I have seen many fitness and wellness influencers (and professionals for that matter) discourage people from participating in higher intensity workouts, claiming “intense workouts can spike cortisol and ruin your hormones!” But this is a massive misunderstanding of how cortisol actually works and in a world where there are already so many barriers to people moving their body, only creates more fear and confusion around exercise.
In this post, we’ll kick things off by looking at some of the myths surrounding cortisol, then for those who want to go deeper, explore cortisol’s true role, how exercise affects it, and why vigorous workouts (even for women) are more friend than foe.
A lot of the misinformation specifically targets women, warning them to avoid higher intensity exercise because it may disrupt their ‘hormones’ in particular cortisol and especially older women or women with conditions such as PCOS.
But the truth is, vigorous exercise doesn’t ruin women’s bodies or hormones (or mens for that matter).
Research shows women do very well with high-intensity exercise. In a randomised trial of pregnant women, an 8-week supervised HIIT program raised cortisol levels (as expected) but did not harm their mood or well-being. In fact, only the HIIT group saw significant improvement in mental health scores.
In another study on women with PCOS, regular High intensity exercise lowered their resting cortisol along with improving many health markers, including visceral fat, insulin and cholesterol markers.
Lets have a look at some of the common misconceptions circulating.
Myths vs Facts:
Myth: “High intensity training spikes cortisol and makes you store fat.”
Fact: Cortisol isn’t an evil hormone, it’s essential for energy and recovery. In reality, short-term cortisol spikes during exercise are normal and even beneficial. This study looking at cortisol levels in cyclists found that while “high-intensity exercise briefly raised cortisol levels, they returned to normal within hours”, in fact, even at the highest intensity levels, cortisol levels returned to baseline after 90 minutes, dispelling the myth of chronically high cortisol from workouts. Additionally, whilst chronically elevated cortisol levels due to stress and other factors may contribute to weight gain in the abdominal area, due to appetite regulation and other mechanisms, it does not occur independently of caloric intake (more on chronic stress later).
Myth: “Women should skip heavy workouts to protect their hormones.”
Fact: Cortisol is the same hormone in women or men. Research shows active women tolerate intense workouts well. Even during pregnancy (as long as there is a history of training prior to pregnancy) or menopause, and even with conditions such as PCOS, studies find that vigorous training is safe and beneficial.
Myth: “Any increase in cortisol is bad for you.”
Fact: Our bodies evolved to use short cortisol surges as signals for action. Post-exercise spikes are like pressing the “stress adaptation” button, over time they lower baseline cortisol and improve fitness. The real problem is failing to rest. With enough recovery, those spikes become positive growth signals.
Cortisol is a steroid hormone made by the adrenal glands during stress (the “fight-or-flight” response). It helps your body respond to challenges by regulating energy and recovery. In practical terms, cortisol does many vital jobs:
Mobilises energy: Cortisol breaks down stored carbohydrates (glycogen) so your muscles have the fuel they need during exercise
Controls inflammation: It helps manage inflammation and repair tissues after stress or workouts, aiding recovery.
Maintains balance: Cortisol supports blood pressure and blood sugar levels.
Manages stress: It’s a key part of the stress response that powers you through short-term challenges.
Because cortisol is so important for basic functions, labelling it “bad” is misleading. Endocrinologist Amber Wheeler says cortisol “helps our bodies adapt to all types of stressors, including exercise”. Exercise physiologist Alexander Rothstein adds that when managed properly, cortisol is a “natural, beneficial hormone that helps you adapt and thrive”. In short, cortisol is like a carefully controlled burst of energy, necessary for life and performance.
The key difference is acute spikes vs chronic elevation. An acute cortisol spike (minutes to hours) is a short-term stress response, like what happens in one workout or a sudden scare. This spike gives you quick energy and then subsides. After exercise, cortisol levels drop and the body switches to recovery mode. after high-intensity exercise it is the body’s ability to recover that ensures these spikes are only temporary.
Chronic cortisol elevation (many hours to days, repeated) is a different story. Constantly high cortisol, from ongoing work stress, poor sleep, or even long term low-calorie dieting, can cause problems. Persistently high cortisol is linked to high blood pressure and metabolic issues. However, exercise-induced spikes are not the same as chronic stress. For instance, studies show that chronically restricting calories or long term low carbohydrate diets actually have far greater impact on cortisol vs occasional high intensity workouts.
In other words, if you find your cortisol is chronically high, check your overall lifestyle – lack of sleep, recovery and inadequate nutrition, will have far greater an influence than a single exercise session.
Bottom line: A workout’s cortisol spike is short-lived and useful, whereas chronic stress or under-fuelling causes harmful long-term cortisol elevation.
When you exercise, your body treats it as a stressor and releases cortisol accordingly. This is by design: cortisol works alongside adrenaline to fuel your effort. During a hard workout, cortisol signals your liver to release glucose and your fat cells to release fatty acids – giving your muscles the energy to keep going. It also temporarily shifts resources away from non-urgent tasks (like digestion), focusing on performance and recovery.
After the workout, cortisol plays a role in recovery. It helps control inflammation and kick-starts repair processes in muscle tissue. In other words, cortisol is part of the healing and rebuilding phase that makes you stronger. The key to managing cortisol, however, is to allow the body adequate time to recover post workout.
If you rest properly between workouts, those cortisol spikes do their job and then subside. Without adequate rest, any stress hormone (cortisol or otherwise) can stay high. But that’s more an issue with a lack of recovery and chronic stress, not the exercise intensity itself.
The reality is, most people aren’t exercising at a high enough intensity for a consistent amount of time to worry about the effects of cortisol due to the actual workout itself.
We need to get the world moving more, not less!
The issue is actually more related to lifestyle related stress. For those who are chronically stressed, the focus should be on monitoring how well your body is recovering from exercise as well as strategies that focus on de-stressing and recovery. Rather than stopping exercise altogether due to fears of cortisol, as the risks associated with inactivity are far greater!
Here are some tips to help you strike the balance between work and rest.
Signs you might be overdoing it:
Regular training actually tunes your stress response system to be more efficient. Each workout is like a controlled stress test: your body learns to handle the burst of cortisol and bounce back. Over time, this makes you more resilient to all kinds of stress.
One study found that people who exercised at least once a week had smaller drops in mood and calmness after a stressful challenge compared to non-exercisers. In plain terms, regular exercisers stay steadier under pressure. Meta-analyses of many trials show the same pattern: moderate exercisers get adaptive signals from cortisol spikes and benefit from them. A recent review even reported that habitual high-intensity interval training lowers resting cortisol levels, even if a single session increases them. So in the long run, fit people tend to have lower baseline cortisol, meaning their bodies aren’t on stress-alert all day.
So rather than wearing out your stress response, exercise (with adequate recovery) primes it. Your body learns “how to be strong” under challenge.
There’s a reason why all official guidelines emphasise that vigorous exercise is part of a healthy routine. The CDC states that adults should get “150 minutes of moderate-intensity physical activity a week” or “75 minutes of vigorous-intensity” a week, plus at least “two days of muscle-strengthening exercise”.
In short, don’t fear cortisol, it’s a natural part of the body’s stress response and a part of what makes you stronger. High-intensity workouts do briefly raise cortisol, but they also make your body more resilient in the long run.
Chronic cortisol can absolutely be an issue. But mainly come from ongoing stress or poor recovery habits, not from a tough workout here and there.
And for women: the evidence is clear – you can handle (and benefit from) a vigorous workout.
So go ahead and do that HIIT class or lift those weights, just make sure to eat, sleep and practise stress management so you recover fully. Your body is resilient and designed to handle stresses. With the right balance, cortisol can become a helpful ally, and not something to fear.