You may have experienced it — that relaxing feeling after a good run. Often referred to as “runner’s high,” the experience is usually attributed to a burst of endorphins released during exercise. But is that truly an endorphin rush you’re feeling, or something else?

David Linden, Ph.D., a professor of neuroscience at the Johns Hopkins University School of Medicine, breaks down the phenomenon of runner’s high and other effects running has on the brain.

What Happens to Your Body — and Brain — During a Run

When you start out on your run, your body goes through a transition: Your breathing may become heavy, and you might notice your pulse quicken as the heart pumps harder to move oxygenated blood to your muscles and brain.

As you hit your stride, your body releases hormones called endorphins. Popular culture identifies these as the chemicals behind “runner’s high,” a short-lasting, deeply euphoric state following intense exercise. Surveys have revealed runner’s high to be rather rare, however, with a majority of athletes never experiencing it. “Indeed, many distance runners feel merely drained or even nauseated at the end of a long race, not blissful,” says Linden.

And though endorphins help prevent muscles from feeling pain, it is unlikely that endorphins in the blood contribute to a euphoric feeling, or any mood change at all. Research shows that endorphins do not pass the blood-brain barrier.

That relaxed post-run feeling may instead be due to endocannabinoids — biochemical substances similar to cannabis but naturally produced by the body.

Exercise increases the levels of endocannabinoids in the bloodstream, Linden explains. Unlike endorphins, 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.

Long-term Mental Benefits of Exercise

The mental benefits don’t stop when you finish your run — regular cardiovascular exercise can spark growth of new blood vessels to nourish the brain. Exercise may also produce new brain cells in certain locations through a process called neurogenesis, which may lead to an overall improvement in brain performance and prevent cognitive decline.

“Exercise has a dramatic antidepressive effect,” says Linden. “It blunts the brain’s response to physical and emotional stress.”

What’s more, the hippocampus — the part of the brain associated with memory and learning — has been found to increase in volume in the brains of regular exercisers. Other mental benefits include:

• Improved working memory and focus
• Better task-switching ability
• Elevated mood

By making running or jogging (or any aerobic exercise) a regular part of your routine, you stand to earn more than just physical gains over time. “Voluntary exercise is the single best thing one can do to slow the cognitive decline that accompanies normal aging,” says Linden.