As a protection mechanism, our brain often convinces us that we are capable of far less than we really are. This is a preservation instinct that is meant to protect your body from over-exertion and from burning through its precious fat-stores.

Our brain relies on its survival skills. It wants your body to expend as little energy as possible to save up for the day when your usual resources are not available. 

If you know that muscles require energy (calories) to sustain themselves, you may already see the picture we’re trying to paint. If your body no longer needs to lift, push, or drag the heavy things, your brain starts to consider your muscles as liabilities instead of assets. They are using more energy than what your activities call for.  

That is why, if you stop working out, your brain responds with “well, we don’t need these anymore!” 

Now, don’t panic. Your muscles won’t completely atrophy as though you’d never seen a day of exercise. In fact, drastic muscle atrophy is really a sign of severe malnutrition, disease, injury, or certain disorders. With less use, your muscles will simply decrease in mass. 

Let’s peer into the details of what really happens to your body when you stop working out. 

At around 2 weeks after stopping exercise, what your body gained from consistent exercise can already start to diminish.  

Several studies, some of which we discuss here, cite cardiovascular endurance and VO₂ maximums (how much oxygen your body can process for energy) as the targets of change within the first 2 to 4 weeks of stopping exercise.  

In a study on the effect of training and detraining (a period of no exercise) on heart rate variability, a group of healthy young men completed 12 weeks of intensive training followed by several weeks of not working out.

The participants all saw an increase in their VO₂ max and in their heart’s overall power after the 12 weeks of vigorous exercise. Once they started the period of detraining, it took about 2 weeks to see a reduction in both of these areas. It took 8 weeks to completely undo the cardiovascular benefits they built from their 12 weeks of training.¹ 

Another study found similar results and cited a period of 2-4 weeks to start seeing the decline.² One spark of hope from this study, however, comes from their comment on current research. This research tells us that the decline can be slowed, and the improvements retained for several months, if training is reduced instead of completely stopped! ²  

We found some interesting insights in a study that compared the after-effects of stopping endurance training with the after-effects of stopping resistance training. The first 24 weeks of the study were spent training and another 24 weeks were spent detraining.  

The researchers found that the participants who strength trained maintained their improvements in strength and lean mass for a longer period of time after stopping exercise than those who endurance trained.³ 

Another study determined that athletes could take up to 3 weeks off from strength training without suffering loss of strength.⁴ This is because muscle gain was quickly returned once they resumed strength training after the 3 weeks.

This is a less frequently researched topic, and there are limitations to current literature on the subject, but some of the findings are still worth looking into. One study monitored blood flow to certain parts of the brain in highly athletic older adults.

With the understanding that exercise has positive effects on the structure and function of the hippocampus (the part of the brain that handles emotion and memory), this study wanted to look into what would happen in this area of the brain if exercise was stopped.⁵