What happens when you stop Exercising?

"An extensive body of clinical evidence shows that regular exercise can reduce and treat depression. However, there is limited research into what happens with depressive symptoms when exercise is stopped," said co-author Julie Morgan from the University of Adelaide.

"Adequate physical activity and exercise are important for both physical and mental health," Morgan noted.

When you suddenly stop your normal exercise routines, just as suddenly the body stops doing a whole lot of beneficial things. As cardiovascular physiologist Andreas Bergdahl explains to George Dvorsky at io9, regular endurance training – such as running – increases the heart's ability to pump blood around the body, our blood vessels' ability to transport it, and the amount of capillaries we have. It also increases the size and number of our mitochondria - the 'power plants' of cells. All of this leads to more efficient use of nutrients and oxygen in the body.

Among other profound benefits is muscle strength, coordination, flexibility, and core mobility.

When we stop engaging our bodies in physical activities, it causes all these measures of fitness to decline – a process known as deconditioning or detraining. And the fitter you are, the faster you tend to lose the benefits of exercise, even if your baseline fitness remains better than average. The first to go is VO2 max, and before you know it, muscle strength, stamina, and coordination follow. You can also expect a rise in blood sugar levels, and even blood pressure.

Despite what some people might think, your muscles won't turn to fat once you stop exercising. They will, however, begin to shrink once you give up an exercise program. If you cut your caloric intake down to make up for not exercising, your muscles would simply get smaller while the overall size of your body would stay about the same. But if you keep eating the same amount you did while exercising, fat will build up and might cover the muscles, which might give the appearance that your formerly fit biceps have turned into flab.

As your muscles shrink and you spend more time on the couch, your physical fitness level will drop. You might start to lose stamina, flexibility and energy within a few weeks of stopping regular exercise. Getting back to exercising can reverse these effects, but it might take time and effort.

If you're an occasional jogger, you aren't likely to experience withdrawal, but athletes and hardcore gym-goers who give up exercise might actually have symptoms similar to those of a recovering drug addict. According to the Counseling and Psychological Services department at the University of California, Santa Cruz, people who exercise heavily every day and use working out to deal with stress may experience withdrawal when they stop.

When we exercise, our muscles process insulin and absorb the resulting glucose as energy. Reduce that energy expenditure and your muscles will adapt physiologically to become a little less insulin sensitive, says John Thyfault, a researcher.

Losing insulin sensitivity means your body converts sugar into fat rather than using it as energy to power your movements. And while that adaptation helped our ancestors survive, it's bad news for the present generation, because improper regulation of insulin can prompt your cells to store some of what's not used in muscle movement as fat. This change puts you at greater risk for the foundation of other conditions, such as Type 2 diabetes.