How Long Does It Take to Lose Muscle?

A fitness pro answers the burning Q "how long does it take to lose muscle?" — and explains what it means to "lose muscle" in the first place.

Woman Flexing Muscles
Photo: Getty Images

No matter how devoted you are to your fitness routine, at some point, you're likely going to take a breather from it. You might go on a month-long cross-country road trip during which you prioritize seeing national parks — not the inside of a CrossFit gym. You may develop a health condition that requires you to chill on the couch for a few weeks. Or, you might simply want to give your body and mind a break from the sweat and grind — and that's okay.

Even if you're content with your workout-free recess, you may still be wondering how much time it takes before you start losing the muscle you've built up over the years — and how long it'll take you to gain it all back if that's something you want. That's why Shape tapped an expert exercise physiologist to answer "how long does it take to lose muscle?" and provide some insight on how you can slow down the process. Trust, your jacked biceps and powerful legs aren't a lost cause.

What It Means to 'Lose' Muscle

In order to answer "how long does it take to lose muscle?" it's important to define what it means to "lose muscle" in the first place. Most often, the "muscle" people are referring to is either muscle size or muscle strength — which aren't entirely correlated, says Alyssa Olenick, Ph.D., C.I.S.S.N, C.F.L.1., an exercise physiologist and sports nutritionist. "Generally, when people gain more muscle, they're going to gain more size and they're going to be able to move more weight and get stronger," she explains.

But your neuromuscular system also plays a role in how much strength your muscles have: As it adapts to training, the motor neurons that connect with muscle tissue are better able to contract the muscles, which creates a force that moves the weight you're lifting, she explains. "So getting stronger is partially developing and recovering muscle tissue, but it's also just the ability to recruit that muscle tissue to produce more force," says Olenick.

How Long Does It Take to Lose Muscle?

If you skip the gym during a week-long trip, don't sweat it. Typically, it takes about two to three weeks to see significant decreases in muscle strength, says Olenick. "If you were to take a vacation for a week and a half and you didn't lift at all, you'll maybe see a little bit [of a decrease] when you come back, but not a ton," she adds. "Your one-rep max probably won't go down that much."

Similarly, you might begin to lose muscle size after taking a week or two off from your usual workout routine, says Olenick. It won't initially be due to a loss of actual muscle mass, but rather a loss of carbohydrates and fluid, she says. ICYDK, your body stores carbohydrates, which can later be broken down for energy during exercise, in your liver and muscles, and these carbs bring water into the muscles with them, she explains. "When you first stop lifting, most of the 'size' you may notice you lose is due to this decreased carbs and water in your muscles, whereas true muscle loss can start within a few days [and] is slower," says Olenick. "The reason you lose the carbs and fluids first is because your body will use them for energy and metabolism, so the storage 'shrinks.'"

That said, the saying "use it or lose it" applies when it comes to maintaining muscle mass and strength. If you're completely sedentary during this time (think: you're on bed rest or have an injury that prevents you from moving), your strength and muscle size may diminish more quickly than if you're staying somewhat active (e.g. going for walks, performing a couple of bodyweight exercises at home, dancing around the house), says Olenick. This muscle loss may be attributed to a reduction in muscle protein synthesis — the process in which your body utilizes amino acids to repair muscle damage caused by exercise, according to research published in the journal Current Opinion in Clinical Nutrition & Metabolic Care. If the breakdown of muscle protein exceeds its synthesis (which again, takes place after a workout), muscle loss can occur, according to an article published in the International Journal of Sport Nutrition and Exercise Metabolism. "But if you're still generally active and moving, it won't be as much [of a decrease], and that muscle will come back quicker than it took to gain it in the first place," adds Olenick.

However, if you used to be a regular weightlifter and have recently switched to exclusively cardio workouts, you may still notice some muscle loss, says Olenick. "While any activity can help preserve muscle, cardio is a form of exercise that is catabolic or 'breaks down' tissue to help create energy for fuel," she explains. "[Still,] the process would be slower than if someone was fully inactive." Her recommendation for runners? Try to do one to three full-body strength workouts per week, and remember to eat enough protein and carbohydrates to support the activity. "Those things will also help their running performance as well," she adds.

How to Measure Muscle Loss

If you're looking for an idea of how much strength you may have lost after taking a well-deserved break, your best bet is to reference your rating of perceived exertion (RPE), says Olenick. This tool is a measure of the intensity of your workout or physical activity based on how hard you think your body is working. So if squatting with 20-pound dumbbells or performing 15 push-ups feels more challenging than it did before your break, that's a sign you may have lost some strength, she explains.

Assessing physical muscle loss is a bit more scientific; you'll need to receive a body composition assessment, such as by using an InBody machine that measures muscle mass, body fat, and total body water content, says Olenick. While you can use a measuring tape to determine if you lost muscle size in the biceps or thighs, for example, that method doesn't give the whole picture: You could have fat gain and muscle loss occur in the same area of the body, so measuring the size of that area may not give you an accurate idea of how much muscle you lost, she explains. Body composition assessments, however, account for those types of recomposition.

What You Can Do to Slow Muscle Loss

While muscle loss — both in terms of strength and size — is likely to happen if you take a break from your usual fitness routine, there are some steps you can take to slow down the process. First, keep your body moving — even if it's not as formal of a workout as you're used to, suggests Olenick. Something as simple as going for a hike or fitting in a quick bodyweight circuit with air squats, push-ups, lunges, and burpees can help you maintain muscle, she adds. Just using your muscles will preserve them and give them a stimulus that says, 'Hey, we're still using you, hang around,'" says Olenick. "Doing whatever you can, even if it seems like a little bit or it's just your bodyweight is so much better than not doing anything at all for maintaining muscle or strength."

You'll also want to stay on top of your calorie and protein intake — if you're not getting enough of either, your body will struggle to maintain the muscle tissue you do have, says Olenick. Your body doesn't necessarily want to give up muscle, but it requires a lot of energy (re: calories) to maintain, she explains. "If you're not eating enough, your body will break down that tissue to use for energy," she says. "So a big thing that helps preserve muscle is eating enough and especially eating enough protein." In fact, people who stick with higher protein intake, even if they're not engaging in any physical activity, will maintain more muscle than those who are short on the macronutrient, she adds.

The good news: When you do head back to the gym, you'll likely regain that strength and muscle mass more quickly than it took you to originally build. Your muscles contain satellite cells (stem cells that are precursors to skeletal muscle and aid in hypertrophy) that are created when you exercise, and these cells will eventually turn into muscle cells, says Olenick. "People who have trained in the past will have more of these satellite cells than people who have never trained before," she explains. "So you have more 'material' to turn into muscle than you did before." What's more, your body is already familiar with the movements you're about to tackle and your brain has established the neural pathways needed to perform the skill, so you'll be able to readapt more quickly — just as if you're riding a bike for the first time after taking a five-year hiatus from the activity, says Olenick.

Still, you likely won't be able to lift the same weight or perform the same amount of sets as you did before your hiatus, so take it easy for the first week or two, says Olenick. During that period, try using a lighter weight or doing one less set for each of your exercises to allow your body to reacclimate and slowly build that strength back up, she says. Most importantly, don't beat yourself up over any strength or muscle loss you do notice, says Olenick. "Give yourself grace for whatever reason that you were taking off training," she adds. "You're back, so what is your body able to do right now? Don't try to push it to do what it was doing before."

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