What Happens to Your Body When You Skip the Gym?

By K. Aleisha Fetters, Life by DailyBurn

No matter how dedicated you are to fitness, sooner or later, it’s going to happen: You’re going to skip a workout… and another… and another. Maybe you can blame a vacation, a mile-high pile of paperwork at the office or just your run-of-the-mill funk. Whatever the reason, before you know it, you’re out of shape.

Neglecting the gym every once in a while is nothing to worry about—after all, sometimes your body needs to rest and recover. But, when you hit pause on your workouts for more than a week, you might actually be throwing your fitness level into rewind.

How Fast Will You Fall Out of Shape?

You worked hard to get fit, whether by logging regular runs, or striving for new personal bests in your bench press. When your workouts fall by the wayside, how fast you fall out of shape depends on more than just how much time you spent away from the gym. Your overall fitness and the type of workout you’re missing will also impact your losses, says James Ting, M.D., a board-certified sports medicine physician with the Hoag Orthopedic Institute in Irvine, CA.

As a general rule, the fitter you are, the longer it will take your muscles turn to flub, he says. Your physique doesn’t like change; it’s constantly trying to achieve homeostasis. So the longer you have been exercising (and the fitter you are), the more time it will take for your body to say, “Well, I guess we don’t need to build muscle any more.”

Related: The Craziest Workout Excuses Trainers Have Ever Heard

If it’s only been a week since you broke a sweat, don’t stress. Whatever your workout history, it’ll take more than seven days for your body to soften. But two weeks? You might not get away with that as easily. One Journal of Applied Physiology study suggests that easing up on your workouts for just 14 days can significantly reduce your cardiovascular fitness, lean muscle mass, and insulin sensitivity. Meanwhile, it can take two months or longer to see complete losses of your fitness gains, according to Ting.

Endurance vs. Strength: Which Will You Lose?

Your body will react differently depending on whether you’re skipping endurance exercise versus strength training, says exercise physiologist and trainer Marta Montenegro, M.S., C.S.C.S.

That’s because your muscles contain both type I (slow-twitch) and type II (fast-twitch) muscle fibers. Type I fibers contribute to endurance performance. Type II fibers are more powerful, and their “fast-twitch” capabilities help you power through high-intensity exercise or strength training.

During your day-to-day activities (like walking, talking, sitting at a desk, etc.), your type I fibers are contributing to the bulk of your efforts. But you really have to work to get your type II fibers to switch into gear. So, when you take a break from exercise, your type I fibers are likely still being used, helping to prevent them from breaking down. But some of your type II, fast-twitch fibers may be rarely, if ever used, if you aren’t working out, she says.

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That may explain why type II fibers tend to atrophy more quickly than type I fibers, she says. In other words, your max bench press will suffer before your 10K time does when you’re slacking. If you’re taking a break from strength work or high-intensity intervals, you’ll notice a huge difference when you finally do go back to the gym.

Endurance athletes aren’t entirely out of the woods, though. When you perform regular cardio, your type II muscle fibers gradually change from type IIx to type IIa, Montenegro explains. Type IIa fibers are key to endurance performance: They are powerful, but don’t tucker out as quickly as IIx ones, meaning they can help power your long runs. When you take a break from your long runs and rides, this essentially reverses, and your percentage of type IIa fibers decreases, while your IIx fibers increases, she says. So prepare to tire out way faster.

Breaks Aren’t All Bad

Before we terrify you into heading to the gym right now, know that it’s actually good for you to skip workouts from time to time. In fact, if you train hard , taking a break can actually help improve your strength, muscle development and aerobic fitness, says certified strength and conditioning specialist Brad Schoenfeld, Ph.D., assistant editor-in-chief of the Strength and Conditioning Journal.

Days off can also improve your mental fitness. “Your body and mind both need time to recover for overall health and in order to achieve optimal performance,” says Ting. “Failing to recognize this and training too hard can lead to fatigue and, ironically, underperformance, the so-called overtraining syndrome.”

If you’re sore more than 72 hours after a workout, you’re feeling ill, or your fitness progress is stalling, it may be time to back off. How long should your break last? “There’s no hard and fast rule for how long a ‘break’ from exercise should be,” Ting says. “It may be as short as a few days, but it’s important to realize as well that it can also be up to one to two weeks without any significant detriment or loss in previous fitness gains.”

Related: Are You Crazy for Working Out While Sick?

Just remember that taking a break from exercise doesn’t (and shouldn’t) equate to gluing your butt to the couch and Netflix-binging. “Taking up some light activity that isn’t part of your typical training regimen, such as yoga or even a long walk or leisurely bike ride, can all constitute a ‘break,’” Ting says.

How to Jump Back Into Your Workouts

Depending on how long you took off—and lazy you were—you might not want to jump back into your workouts, but rather ease into them. If you’ve taken any more than a couple weeks off, you’ll probably notice some differences. After a month or more, you’ll definitely want to get started with a less-intense version of your regular workout, Ting says.

“The most important thing is to back off a little for the first week,” Schoenfeld says. “Choose a weight where you will be able to stop several reps short of failure on your sets. The following week you should be able to train at your previous level, assuming the reason for stopping wasn’t an illness or injury.” Meanwhile, if you’re getting back into running, start at a pace at which you can run comfortably and are able to speak in short sentences. After a week, try turning up the speed.

It can be frustrating to exercise at anything less than your max effort, sure, but gradual is the way to go to prevent injury. The last thing you want is to walk into the gym after a month off, try to squat your “usual” load, and throw out your back. (Hello, another month off.)

Luckily, when it comes to getting back into your pre-break shape, you do have muscle memory working for you, Schoenfeld says. There are two aspects to muscle memory. One involves your ability to carry out movements in a coordinated fashion. Wonder why your first rep on the bench press looked so sloppy? It’s because your body was learning which muscle fibers it needed to recruit, and which ones it didn’t, to properly perform the exercise.

Then second component of muscle memory involves your cells. “Muscles have satellite cells—basically muscle stem cells—that help to drive protein synthesis. Resistance training increases satellite cells and these changes remain for years,” he explains. “So even if muscle is lost from taking time away for many years, a person can regain the lost muscle much more quickly after an extended layoff.” Score.

Exactly how long it takes will vary from person to person, but by and large, you can expect to be back in fighting shape in a few weeks.

Related: 7 New Recovery Tools You'll Love to Hate