Why does exercise make us feel good?

The heart’s pumping, the lungs are sucking in more oxygen and there’s a healthy burn in the muscles from a well-managed workout.

Which is great. But none of that explains why the anxiety or depression you were feeling before hitting the gym or the footpath seems to have lifted, or at least lightened.

Where does this surge of calm come from?

A popular idea, long supported by medical thought, was that endorphins – hormones that work similarly to opioids – were responsible for an exercise-related lift in mood.

Endorphins, though, are an analgesic. They give some protection against muscle pain, but because they don’t cross the brain-blood barrier, it’s not possible that they affect mood.

This reappraisal of endorphins and their role in exercise is relatively new.

Meanwhile there’s growing evidence that exercise does improve mood – and the quality of life for people with mental health issues.

A growing body of evidence suggests that exercise is as effective a treatment for moderate depression as antidepressant drugs or behavioural therapies – for some people, but not all.

What is mechanism at work here?

A 2019 study linked this boost in mood with increased levels of cannabis-like chemicals produced by the body.

The study involved a group of women suffering a major depressive disorder. Those who exercised at a prescribed level of intensity experienced a short-term improvement in mood.

The chemicals at work are known as endocannabinoids.

The researchers concluded that it was “plausible” the production of endocannabinoids “contributes to the mood-enhancing effects of prescribed acute exercise”.

Since then, the relationship between endocannabinoids and a boost in mood has been widely talked up.

A report from Johns Hopkins University School of Medicine found that endocannabinoids “can move easily through the cellular barrier separating the bloodstream from the brain, where these mood-improving neuromodulators promote short-term psychoactive effects such as reduced anxiety and feelings of calm”.

What are endocannabinoids?

According to an explainer from the University of Sydney’s Lambert Initiative for Cannabinoid Therapeutics, endocannabinoids appear to have evolved in the brain to maintain biological harmony and reduce excessive and damaging excitability of neurons.

They also play a role in neuronal plasticity, that is, how the brain adapts to change.

Overall, then, these are chemicals designed to keep the body on a steady course.

This is complicated work and scientists are still working out how the endocannabinoid system works, and a complete picture of what it does.

Exercise reduces inflammation

People with sore knees tend to think it’s exercise that causes inflammation. The evidence shows that exercise actually reduces inflammation throughout the body.

Studies have shown exercise helps reduce pain caused by arthritis. Photo: Getty

A new study suggests endocannabinoids are involved in this reduction of inflammation –  with the authors proposing that this mechanism could be exploited to “treat certain conditions such as arthritis, cancer and heart disease”.

A group of scientists, led by Professor Ana Valdes from the School of Medicine at the University Nottingham, tested 78 people with arthritis.

Thirty-eight of them carried out 15 minutes of muscle strengthening exercises every day for six weeks, and 40 did nothing.

At the end of the study, participants who did the exercise intervention had reduced their pain.

And they also had more gut microbes of the kind that produce anti-inflammatory substances, lower levels of cytokines (chemicals that signal inflammatory responses) and higher levels of endocannabinoids.

A significant and surprising finding is that the increase in endocannabinoids was strongly linked to changes in the gut microbes.

At least one third of the anti-inflammatory effects of the gut microbiome was due to the increase in endocannabinoids.

Doctor Amrita Vijay, a Research Fellow in the School of Medicine and first author of the paper, said: “Our study clearly shows that exercise increases the body’s own cannabis-type substances. Which can have a positive impact on many conditions.”