How Fast Do You Actually Lose Fitness?

Kirk Campbell, MD, assistant professor of orthopedic surgery at NYU Langone in New York City, says that fitness loss is inevitable if you stop exercising for an extended period of time — no matter how fit you are. But exactly how quickly you lose fitness and how much you lose depend on both your personal circumstances and what kind of fitness you’re talking about.

Endurance athletes like runners, cyclists, swimmers, and dancers build up cardiovascular fitness (also called aerobic fitness or endurance) over sustained, consistent cardiovascular training.

This type of fitness won’t disappear in a matter of days, but it will decrease over time, according to Dr. Campbell. Generally, he says, cardiovascular fitness starts to noticeably decrease after about two weeks of being sedentary.

There’s not much evidence on how fitness continues to decrease after several weeks of total inactivity, but those in “good cardiovascular shape will take up to a few months to completely lose all of [their] aerobic fitness,” Campbell says, adding that the timeline is relative to each individual’s capabilities.

Also keep in mind that unless someone is injured, a break in their regular exercise rarely means complete inactivity. In the literature review cited above, the evidence suggests that cardiovascular fitness of regular exercisers starts to decrease significantly after about 35 days (five weeks) of occasional, light exercise. So, that means if you were exercising a lot and then drastically reduce the intensity of your workouts, you might also notice a decrease in cardiovascular fitness.

Even though you’ll lose some fitness with breaks from training, periods of rest are still really important for the body — and the mind — especially after periods of arduous training. “Recovery is important from both a physical and mental standpoint,” says Campbell — it allows you to make greater fitness gains in the long run.

Running coach Neely Gracey, certified by the Lydiard Foundation and based in Denver, says she’s always taken a scheduled two weeks off at the end of each marathon season. She encourages her athletes to do the same. “Some want more time, some want less, but a period of no running to allow the body and mind to rest and reset is important,” Gracey says.

The five-time Team USA competitor says time off helps athletes avoid injury from muscle overuse, and it also helps reduce burnout, a sentiment which Campbell echoes: “Taking a break from working out can be beneficial [to] avoid burnout.”

However, there’s a notable distinction between intentional time off (like following an endurance event) and unintentional breaks in exercise (where you have no plans of getting back into a routine). In other words, a short break can be beneficial to avoid burnout and injury, but taking time off shouldn’t become a long-term lifestyle choice.

Another option is to take periods of active recovery, which includes doing low-impact activities like yoga, stretching, easy biking, house cleaning, or gardening. This can help reduce the risk of losing fitness.

Why? Returning to exercise after a long break comes with its own mental and emotional challenges.

Kelly Gillen, a runner who completed the JFK 50 Mile in November 2016, struggled mightily in this department. Logging double-digit-mile runs had been the norm, but after months of not running, 10 miles suddenly seemed “insurmountable.” “It’s definitely a mental thing [that was] really hard at the beginning,” Gillen says.

1. Keep Moving Throughout the Day

“No matter your fitness level and how that changes throughout your journey, there are many ways to get activity into your day,” says Kayla Jeter, a Road Runners Club of America–certified running coach and WW D360 coach based in Chicago. Body-weight exercises (no gym or equipment required), hiking, or or even gardening are good options, she adds.

Campbell recommends light training, including body resistance exercises that don’t lead to an elevated heart rate, to limit the loss of strength, and points to the proliferation of fitness apps as aiding this endeavor. Of course, if you’re taking a break due to injury or for another medical reason, it’s important to clear all activity with your doctor.

2. Don’t Underestimate Body-Weight Movements

While die-hard runners may find strength-training exercises alone an inadequate substitute for multi-mile runs, exercises that work the body’s muscles and encourage flexibility are crucial if limiting fitness loss is the goal, Jeter explains.

Campbell recommends bodyweight exercises like squats, lunges, and push-ups (which you can modify to do on your knees) to limit strength loss, and regular stretching to maintain flexibility. There are countless fitness apps and videos out there, many of them free, that can guide you through short body-weight workouts.

3. Prioritize Strength Training

While taking a break from running to recover from injury, Gillen focused on strength. She worked mostly with kettlebells, doing squats, deadlifts, and swings to help strengthen her glute muscles and her body overall. She considers her months-long running break to be time well spent, because ultimately, the strength building made her a better runner. She now relies less on her quadricep muscles because her glutes are activated, which reduces her injury risk. Five years later, she still integrates kettlebells into her exercise routine.

• You don't lose fitness overnight, but measurable declines can start within a few weeks of stopping exercise.
• Aerobic fitness (like endurance and VO2 max) typically declines faster than strength.
• Muscle size and strength tend to decrease more noticeably with longer breaks, especially beyond several weeks.
• Staying even lightly active during breaks can help slow fitness loss and make it easier to bounce back.