What Happens When You Stop Exercising?

When you stop exercising, your body may show signs of deterioration in a week, and more seriously after three. Recovery is harder for older people, but don't give up.

You were regularly working out — building both aerobic capacity and muscle strength. Your workouts improved your coordination, stability, and flexibility, while keeping your blood sugar and fat levels low.

But then you were injured and it’s taking weeks to recover. Maybe you got a flu and fell out of the habit of exercising. Maybe you’re in a rough spell at work and can’t make it to the gym — and you don’t know how long that will last. Maybe you have a strained budget, dropped a gym membership, and haven’t figured out ways to exercise on your own.

When that activity comes to a halt, your body suffers. Exercise physiologists might refer to you as “apparently healthy but deconditioned.” The fitter you are, the faster you’ll lose stamina, strength, and coordination, though you’ll still end up ahead of someone who never exercised at all. After 10 to 28 days of sedentary living, anyone who works out regularly will see noticeable changes.

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Highly trained athletes tend to show a drop of aerobic endurance within three weeks of detraining, but even after 12 weeks they will still retain a significant amount of bulk strength and endurance. They can expect a rise in blood sugar levels and blood pressure.

For example, a man who can run 5 kilometers in 20 minutes will usually need about 24 minutes if he hasn’t been running for a month or two, calculates Harry Pino, PhD, a manager and clinical exercise physiologist at the Princeton Longevity Center in New York.

That can be discouraging, and it doesn’t help that it takes longer to recover your capacity to exercise than it does to lose fitness.

What about muscle mass? After getting great results with weight training for the first time, it’s easy to worry about losing those hard-won abs and pecs. A week away, say while on vacation or finishing a big project, won’t hurt.

Worry more when a break lasts for months. In one study, people ages 20 to 30 lost from 6 to 10 percent of their strength in a knee when they stopped training for 31 weeks, with most of the loss coming after the first three months. A group of 65- to 75-year-olds lost almost twice as much strength as the younger set.

Women in the study did just as well as men both in building strength and maintaining it. In another study that tested muscle strength after a training program, however, women ages 65 to 75 lost all their gains after 31 weeks of detraining. Men and women in their 20s, and men ages 65 to 75, did keep some of their gains.

Muscle mass, and the ability to create and maintain it, declines with age. After age 50, people who don’t exercise lose up to 0.4 pounds a year in muscle. Although there’s debate about how long athletes can keep up their performance, it looks like even contestants in the Senior Olympics gradually do worse in track and field events as they age.

Some people worry that their muscles will turn into fat. Actually, muscles atrophy and fat cells expand, so you look and feel bloated and round compared to your fit physique. You’re likely to gain weight, and many people feel a decline in mood and self-confidence. Smaller problems may make you feel more stressed because you haven’t been training your body to handle challenges.

At any age, strength is kind of a big deal. Muscles aren’t just for moving furniture. Evidence shows that being stronger, not just thinner, helps decrease your risk of type 2 diabetes, for example. Also, strength is linked to less risk of memory decline and Alzheimer’s disease.

Use it or lose it definitely applies to muscles, but the loss isn’t necessarily permanent. Strength exercises still work for anyone after time off. So does aerobic exercise.

During your off period, look for exercises you still can do. Try biking if you can’t run because of a knee problem. Can’t get to the gym? Lift soup cans at home and do squats and push-ups. While traveling, look for opportunities to walk rather than taking an Uber. Then get back into a routine, without pushing yourself so hard you get injured.  

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