How Fast Do You Get Out of Shape?

Learn how fast you lose fitness, how long it takes to lose aerobic capacity, and how quickly you lose muscles.

Ben Greenfield
4-minute read
Episode #22

We’ve all had those times when it seems impossible to exercise. Whether you have social obligations, travel plans, a nagging injury, or the loss of a gym membership, even the most perfect workout routine can become suddenly interrupted. When this happens, how fast do you lose those fitness results for which you’ve been working so hard? How long will it take for you to begin sucking wind again when you climb a flight of stairs, noticing your stomach becoming soft again, or losing the size or shape of your arms? In this article, you’ll find out how fast you lose fitness and more importantly, what you can do about it.

How Fast Do You Get Out of Shape?

There have been a couple studies that have investigated how quickly you lose your lungs’ ability, also known as your aerobic fitness, or your cardiovascular system’s ability to use oxygen and create energy. Interestingly, there is a significant difference between how quickly fit folks lose this fitness compared to beginner exercisers.

One study observed that conditioned athletes who had been training regularly for at least a year and then suddenly stopped lost half of the aerobic conditioning after 3 months.

In contrast, research shows that beginner exercisers who have worked out for about 2 months experience a complete loss of all aerobic conditioning after 2 months of not working out.

What Causes the Loss of Aerobic Fitness?

This loss of aerobic conditioning occurs as your lungs slowly lose elasticity, your mitochondria (oxygen utilizing cell components), begin to decrease, blood vessels shrink in size, the heart pumping volume decreases, and you even experience increased sensitivity to exercise discomfort. So if you’re going to quit exercising, you may want to think about getting into pretty good shape first!

How Fast Do You Lose Muscles?

Even if you can’t do a six day a week, perfect cardio and strength exercise routine, you should still stay physically active, and you can try to exercise at least once per week.

And what about muscle strength, muscle mass, or that nice, toned appearance you’ve been trying to achieve? In exercise physiology, we call a loss of muscle fitness “disuse atrophy,” and that refers to an actual loss of muscle mass or muscle tissue due to, as you would have guessed, disuse. When disuse atrophy occurs, your muscles begin to decrease in size and appear less toned. So yes, as you’d probably guessed, the “use it or lose it” philosophy certainly applies when it comes to your muscles.

Interestingly, because your muscles are comprised of different types of fibers, you don’t just lose muscle mass when you stop exercising; you also experience a conversion of your slow-twitch endurance muscle fibers and fast-twitch strength-producing muscles fibers to easily fatigued “couch potato” muscle fiber types. So your body doesn’t just lose muscle, but the type of muscle it has actually changes!

Surprisingly, disuse atrophy and muscle fiber type conversion can occur in as little as 72 hours, and, similar to aerobic fitness, the degree of atrophy depends on how often the muscle is used. Muscles, such as the hamstrings, which we tend to use quite often in every day activities such as standing, will tend to atrophy slower than muscles that we use less often, such as the quadriceps. And the fitter the muscle, the slower it will atrophy.


All content here is for informational purposes only. This content does not replace the professional judgment of your own health provider. Please consult a licensed health professional for all individual questions and issues.

About the Author

Ben Greenfield

Ben Greenfield received bachelor’s and master’s degrees from University of Idaho in sports science and exercise physiology; personal training and strength and conditioning certifications from the National Strength and Conditioning Association (NSCA); a sports nutrition certification from the International Society of Sports Nutrition (ISSN), an advanced bicycle fitting certification from Serotta. He has over 11 years’ experience in coaching professional, collegiate, and recreational athletes from all sports, and as helped hundreds of clients achieve weight loss and fitness success.