Cortisol and exercise: What you need to know

This is part three of our four-part series of stories exploring stress, the nuances that come with the psychological and physiological response and its relationship with running. Read part four here.

You might already be aware that cortisol is known as the 'stress hormone'. But why?

As explained by Justin Mullner, a primary care sports medicine physician with the Orlando Health Jewett Orthopedic Institute, cortisol is released from the adrenal glands – located on top of each kidney – in response to stressors. A stressor is anything that activates the stress response in your body, while stress is the resulting neurological and physiological response.

'The issue with nicknaming it the stress hormone is that it creates a negative association with cortisol, and this could not be further from the truth,' says Alex Rothstein, a certified strength and conditioning specialist, exercise physiologist and coordinator in the Exercise Science Program at New York Institute of Technology.

Activating your body’s sympathetic nervous system – also known as your fight-or-flight response – is only part of cortisol’s role in the body. 'Because most of the tissues in the body have receptors for cortisol, it’s a hormone that can interact with most of the body's systems,' says Rothstein. 'It’s a critical link in maintaining homeostasis and helping to regulate the body.'

For example, cortisol helps to suppress the body’s inflammatory response, regulates blood pressure, blood sugar and metabolic reactions in the body, and helps to control your sleep-wake cycle.

It’s your brain’s job, in conjunction with the pituitary gland – an endocrine gland at the base of the brain that produces hormones – to regulate how much cortisol your adrenal glands produce, so the levels in your body don’t go askew and negatively affect those important functions.

Exercise is a stressor. According to research published in the Expert Review of Endocrinology & Metabolism, breaking a sweat 'serves as a robust activator of the neuroendocrine system, provided that the exercise is of sufficient volume [in terms of intensity and/or duration].'

Physiologically, exercise causes a chain reaction that stimulates cortisol production. The brain’s hypothalamus secretes certain hormones in response to exercise, which activates the anterior pituitary, explains Mullner. The anterior pituitary controls the function of several other endocrine glands and eventually stimulates the adrenal glands to release cortisol.

In other words, when you exercise, your body goes into a high-alert mode. During exercise, your body downgrades certain functions, like digestion, while prioritising those that are essential to the stressful situation, like increasing the amount of glucose in your blood for quick energy.

When your body starts to feel the stress of moderate or high intensity exercise, your cortisol levels do increase – but it’s a short term surge that serves a larger purpose. 'Stimulating the release of cortisol through regular exercise is an excellent and healthy way to regulate your stress response,' says Rothstein. 'It’s a dose-response relationship – the body learns the appropriate amount of cortisol to release in response to various levels of stress by experiencing various levels of healthy stress.'

So, that post-workout influx of cortisol is a good thing. Just like progressive training helps your body to adapt to a higher load, increasing cortisol in your system helps your body to better handle similar stressful situations in the future.

Here’s a simple, running-specific example from Mullner. 'If you increase your [mile pace] from eight minutes to six minutes, your body releases less cortisol in response to the same load as before,' he explains. 'If you can now run a six-minute mile, running an eight-minute mile will be less taxing on your system and less cortisol will be released as compared to when you could only run an eight-minute mile at your best.' That also improves how your body will react to other stressors, like a scary, unexpected email from your boss or an argument with a friend.

There is such a thing as too much of a good thing. 'An exercise load far in excess of what your body is adapted to can cause a massive release of cortisol, which is ultimately catabolic and can interfere with the body’s attempts to recover and adapt to the exercise stimulus,' says Mullner.

Releasing excessive amounts of cortisol in response to excessive amounts of exercise is a protective measure by your body, he adds. But, when you’re in a catabolic state, that means your body is breaking down fat or muscle – and recovery is when your body should be repairing muscle.

'Too much of anything creates a problem, and if you are constantly stressing out your body and causing it to release cortisol, then you are constantly breaking the body down and never giving it its 'rest and digest' (parasympathetic nervous system) phase to recover from the stressful experiences,' says Rothstein.

When your body is stressed to the max and starts pumping too much cortisol into your system, you’re likely to feel fatigued and lose motivation. As Mullner says, that’s a red flag alert meant to communicate that you’ve pushed past your limits.

It's worth noting that people who participate in endurance sports – like distance runners, for example – are more likely to risk cortisol imbalances, as they spend a significant amount of time putting their body under physical stress. This is associated with elevated cortisol exposure over prolonged periods of time, according to older research published in Psychoneuroendocrinology.

A 2019 study in the BMJ Open Sport & Exercise Medicine even found that elevated cortisol is a potential biomarker of overtraining syndrome. The symptoms of overtraining include an elevated resting heart rate, sleep disturbances, a lack of appetite or weight loss, frequent colds and viruses, impaired recovery, higher perceived effort for the same sessions and a lack of motivation. Much of this overlaps with chronically elevated cortisol levels, also known as chronic stress.

This isn’t something that most people should overthink. Unless you’re dealing with really severe symptoms that could indicate a more serious cortisol imbalance, you don’t really need to be doing regular blood, urine or saliva tests to check your cortisol levels.

What you do need to do is learn how to manage your stress. It’s important to remember that exercise is always a stressor, and that stress is additive – our bodies can’t distinguish between your intense track session and a stressful day at work, for example. Research published in Psychotherapy and Psychosomatics refers to this as 'allostatic load', which is essentially the wear and tear on your body. Once your total stress levels exceed what you can cope with, you'll suffer poorer health outcomes.

Further studies prove this. According to 2016 research in the International Journal of Sports Medicine, stress generated by negative life events impaired both running economy and recovery. Meanwhile, a 2012 study published in Frontiers in Physiology found that people with higher stress levels failed to show fitness improvements over a two-week period.

If you’re feeling overwhelmed, practicing breathwork can help you to chill out in the short term. In fact, a 2023 meta-analysis published in Scientific Reports suggested that breathwork was an effective means of reducing stress and improving mental health.

According to a 2021 review, practicing mindfulness – a mental state where you prioritise being present – can also help to significantly reduce anxiety, depression, psychological distress and stress levels. Using visualisation, making positive affirmations, reaching out to loved ones, listening to music and doing low intensity exercise are all proven ways to relieve stress when you need to chill out fast.

However, if tension lingers, you might want to tone down the intensity and frequency of your workouts – especially if that stress has been hanging around for several consecutive days.

'People need to be more mindful of their daily, acute exercise loads as well as their more chronic workloads so that there isn’t too much of a spike above what you have trained yourself for,' says Mullner. 'Your body is very resilient and can handle incredible amounts of work, so long as it is properly prepared and adapted. Optimising your recovery through nutrition, sleep and stress relief can also go a long way to minimising the negative effects of cortisol.'

When you give your body the time it needs to rest and repair itself post-workout, cortisol will help you to make gains – not impair that ability.