Your mood may plummet.
Studies suggest that cardio can be just as effective at boosting your mood as prescription antidepressants.
Your body produces endorphins - hormones that make you feel good - when you exercise, along with other happiness-inducing chemicals like serotonin, dopamine, norepinephrine, endocannabinoids (our bodies’ own marijuana-like chemicals), and more, Dr. Ratey says.
What’s more, recent research in the New England Journal of Medicinesuggests that working out sparks the production of proteins called myokines, which can help protect your brain from stress-induced depression.
So when you stop exercising, you miss out on the influx of these mood boosters, Dr. Ratey says. And you may end up feeling down as a result.
In fact, when 40 regular exercisers stopped working out for two weeks, they scored worse on a mood test that measured depression, tension, and anger than those who continued to work out, according to a study in Psychosomatic Medicine.
Your memory may falter.
When University of Maryland researchers scanned the brains of fit older athletes, they found that blood flow to the athletes’ brains - particularly to the hippocampus, a structure involved in learning and memory - dropped significantly after a 10-day exercise hiatus.
In this study, the reduced blood flow wasn’t linked to any declines in brain function, says study author Dr Alfonso Alfini. But other research has linked less blood flow to the hippocampus to mild cognitive impairment and Alzheimer's disease, he says.
It may be that the decreased blood flow makes it more difficult to learn or develop new memories, says Dr Devi Nampiaparampil, a pain management physician at NYU Langone Medical Centre.
Your body also produces less of a protein called cathepsin B, which has been linked to improved memory, when you stop working out, a new study in Cell Metabolism suggests.
You may become less sharp.
In a study from Finland, scientists rounded up 10 pairs of identical male twins who exercised regularly.
One twin in each pair stayed active - working out twice a week - while the other exercised less.
After three years, the more active twins had more grey matter - tissue in your brain that is key to processing information - than their less-fit twins.
Exercise strengthens your all parts of your brain tissue, including grey matter, Dr. Ratley says. This makes your brain more resistant to stress and ageing.
So if you stop working out, your grey matter may take a hit, potentially setting the stage for problems processing information and thinking critically.
You may have trouble concentrating.
A review of research published in the British Medical Journal concludes that even short bursts of exercise - 10 to 40 minutes - lead to an immediate boost in concentration.
The boost is at least partly thanks to the increased blood flow to your brain. It may also relate to the higher levels of chemicals in your blood, like endorphins and certain hormones, that keep your brain on high alert, the researchers speculate.
So when you stop exercising, blood flow and these chemicals both drop - possibly leaving you with a poor attention span.