For Years, Scientists Believed the Phenomenon Was Caused by Endorphins, the Body’s Natural Opioids

Others as calm, clarity or even a sense of being completely absorbed in the moment. Many people experience some version of it after a long run or a spin class. But more recent neuroscientific research now indicates that this might not wholly be the case.

Instead, a runner’s high appears to emerge from several brain systems working together. This explains why a runner’s high has so many far-reaching effects – and why these effects can often persist long after the initial experience of euphoria. Endorphins are naturally-occurring brain chemicals which are released during periods of physical stress help to reduce pain.

Aerobic exercise increases circulating endorphins. Numerous studies have demonstrated higher levels of the endorphin beta-endorphin following prolonged aerobic exercise, such as running. This is why endorphins were long believed to be the sole cause of a runner’s high.

But there’s a key problem with the endorphin theory. This is because endorphins circulating in the blood struggle to cross the blood-brain barrier – the tightly regulated system that protects the brain from substances in the bloodstream. So while endorphins may well contribute to pain relief elsewhere in the body, they cannot fully explain the feelings of euphoria and emotional wellbeing generated by a runner’s high within the brain itself.

So scientists began searching for another explanation. The breakthrough came with the discovery that exercise also activates the endocannabinoid system. Endocannabinoids are naturally produced by our bodies.

They help with functions such as pleasure, memory and stress regulation. One of the most important chemicals produced by the endocannabinoid system is anandamide, one of the brain’s natural “feel-good” chemicals. It helps to reduce anxiety, ease pain and create feelings of calm and wellbeing.

And, unlike endorphins, anandamide crosses the blood-brain barrier with ease. After a long bout of aerobic exercise, blood concentrations of anandamide rise substantially. Once inside the brain, it activates cannabinoid receptors in regions involved in emotion, motivation, reward and pain perception.

The resulting effects are remarkably similar to many features of the runner’s high – including reduced anxiety, better movement, less pain and feelings of calm. This isn’t to suggest that endorphins play no role in a runner’s high. Modern neuroscience suggests endorphins and endocannabinoids work together – with endocannabinoids probably playing the larger role in producing the emotional aspects of the experience.

Several other neurotransmitters also play a part in a runner’s high. Dopamine, which is central to motivation and reward, helps reinforce actions that are beneficial for survival. Rather than simply producing pleasure, dopamine encourages us to repeat a behaviour that the brain considers valuable.

Serotonin contributes to emotional stability and wellbeing, while noradrenaline enhances alertness and focus. Exercise also stimulates the production of brain-derived neurotrophic factor (BDNF), which supports the growth of new and existing brain connections and plays a vital role in learning and memory. Although BDNF probably doesn’t produce the immediate euphoria associated with runner’s high, it may help explain why regular running can improve various aspects of wellbeing. A runner’s high is about far more than pleasure chemicals.