Whether you’re in it for the aesthetics or the many health benefits, there’s no denying that building and maintaining muscle mass is a good thing. But, as anyone who’s worked hard to make gains knows, hanging onto that muscle can sometimes be easier said than done. Several factors—some common and some sneaky—can steal muscle mass away, sabotaging your fitness goals and overall health and well-being. 

If your gains (and strength) are disappearing right before your eyes, one of the following muscle thieves might be to blame.

• ABOUT OUR EXPERTS: Mary Sabat, R.D., C.P.T., is a dietitian, personal trainer, and the founder of Body Designs by Mary. Michael Masi, D.P.T., is a physical therapist and an expert contributor for Garage Gym Reviews.

1. Severe Calorie Cuts

When trying to lose weight, many of us automatically think that cutting calories is the way to go, but if we slash calories too much, we run the risk of losing muscle. “Severely restricting calorie intake can lead to muscle loss because the body starts breaking down muscle tissue for energy when it doesn’t get enough calories from food,” shares dietitian and personal trainer Mary Sabat, R.D., C.P.T., founder of Body Designs by Mary.

Fix it: If you’re trying to lose weight, Sabat recommends sticking with a moderate calorie deficit of around 300 to 500 calories below your maintenance intake. Also, when cutting calories, make sure to put extra emphasis on eating nutrient-dense foods and protein to support muscle health. (More on that later.) Of course, if counting calories stresses you out, you can lean on a number of other strategies for supporting weight loss instead.

2. Too Much Stress

While the stress lifting heavy weights puts on your muscles can be a good thing, the chronic stress that comes with working too much, drama-filled relationships, and the like certainly isn’t. You see, chronic stress increases the production of cortisol, a hormone that can hinder muscle growth and promote muscle breakdown when present in high levels over prolonged periods, explains Sabat. If you’re stressed 24/7, you can bet that your gains will suffer.

Read More: 6 Physical Signs You’re Way Too Stressed

Fix it: One of the best ways to combat stress is to practice stress-reduction techniques like meditation, mindfulness, or yoga, says Sabat. That said, prioritizing any activity you enjoy that brings you peace and stress relief is worth doing. Some other ideas: drinking a warm mug of tea while reading a book, going for a walk outside, or catching up with a good friend over the phone. Of course, in some cases, checking in with a mental health professional is an important step in getting stress under control. 

3. Rapid Weight Loss

Rapid weight loss, especially without proper nutrition, can indeed result in fat loss—but consider yourself warned: it means parting with plenty of muscle mass, too. According to Sabat, this occurs because the body uses both fat and muscle tissue to meet its energy needs amidst incredibly quick weight loss. 

The steeper and quicker the weight loss, the more likely the body is to break down muscle for energy, notes physical therapist Michael Masi, D.P.T., a member of Garage Gym Reviews’ expert panel.

Fix it: If you want to lose weight without sacrificing muscle, aim for a gradual weight loss of one to two pounds per week, suggests Sabat. Masi also recommends focusing on weight loss for no longer than three months before taking a break by reintroducing some calories and maintaining that current weight for a given period before continuing.

The reason for this? “As you continue to lose weight, your return on each intervention—whether that be eating less or moving more—diminishes,” remarks Masi. “Eventually, taking a break from dieting can help reset your sensitivity to a caloric deficit.”

4. Not Moving Enough

According to the National Academy of Sports Medicine, lack of activity for an extended period is the number-one cause of muscle mass loss. “Inactivity reduces muscle use and stimulation, causing muscle fibers to weaken and shrink over time,” explains Sabat.

The fix: If you’re here, you probably have no problem staying active. Just for good measure, though, the general rule of thumb for maintaining muscle mass and strength is to regularly incorporate resistance training into your routine, remarks Sabat. Two or more days of muscle-strengthening activities is the minimum.

The reason regular resistance training is so important: “The body is less likely to break down tissues that it deems as necessary for overcoming the stimuli (like lifting heavy weights) that you encounter,” Masi explains.

5. Falling Short On Protein

As you (hopefully!) know, protein is essential for muscle maintenance and repair. So, if you don’t eat enough protein, your body cannot adequately rebuild muscle after it is broken down during training, explains Sabat. Over time, this can lead to stalled gains or even muscle losses, even despite a spot-on training routine.

Fix it: According to Masi, prioritizing protein is a must for anyone interested in maintaining or gaining muscle—particularly if you’re also whittling down the calories.  “If you have low calories but sufficient protein, the stimulus of resistance training helps the body prioritize which stored energy sources—a.k.a. muscle—to keep,” he says. 

How do you make sure you are eating an adequate amount of protein? Sabat recommends consuming around 1.2 to 2.0 grams of protein per kilogram of body weight per day. If you weigh 150 pounds, for example, that’s between 82 and 136 grams of protein per day. (Here are nine easy ways to up your protein intake.)

6. Skimping On Sleep

Sleep is essential for all areas of health—and muscle recovery and growth are no exception. The primary issue here is that inadequate sleep disrupts the regulation of growth hormone and testosterone, both of which play key roles in muscle recovery (yes, in both men and women).

Fix it: To ensure you’re getting the rest you need to hang onto that precious muscle, Sabat recommends prioritizing seven to nine hours of quality sleep each night. That said, if you’re under particularly stressful conditions, such as dieting or a block of harder training, you might want to shoot for more like eight to 10 hours, suggests Masi. 

7. going Too Hard On HIIT

You may enjoy those high-intensity interval training (HIIT) workouts, but going hard on them too often can lead to muscle breakdown because doing so leaves the body without enough time to repair itself, explains Sabat. “Intense workouts without proper recovery time can lead to muscle breakdown instead of growth, as the muscles remain constantly stressed.”

Fix it: Maintain that muscle mass you work so hard for in the gym by allowing for sufficient recovery time between HIIT sessions. Sabat also recommends incorporating lower-intensity workouts or full-on rest days to prevent overtraining.

Many factors determine just how much time you need for recovery between HIIT workouts. “The level of intensity is one of these variables,” says Masi. “Other considerations include diet, as you will typically need more rest if you are in a caloric deficit, and/or if you have other external stressors adding to your cumulative fatigue.” Generally, experts suggest that well-trained individuals (a.k.a. workout vets) can handle between three and five HIIT sessions per week, depending on those other variables.

8. Working the same muscles back-to-back

Whether you’ve heard of the fitness term “repeat exposure” or not, you’re probably guilty of committing this crime against muscle mass, according to Masi. “Repeat exposure” refers to training a particular muscle group repeatedly without adequate recovery time between sessions. 

“This is mostly problematic when training the same muscle group back to back (e.g. exercise splits in which you squat multiple days in a row). With this type of exercise programming, you may call upon the same muscles you just trained to failure the day before, which is a losing strategy, Masi explains.

Fix it: If your performance is lacking or your rate of perceived exertion feels higher than usual, chances are you need more time before working a given muscle group again. “If a set inexplicably feels heavier than it usually does and yields fewer repetitions than you have done in the past, that is a good indication that you have not recovered enough since your last training session and may need to take another day or adjust your programming,” Masi says. 

When To See A Health Professional

While some muscle loss can be chalked up to an unbalanced training routine and extreme dieting strategy, there are certainly some circumstances in which disappearing muscle warrants more serious inquiry.

“Unexplained weight loss in general is a pretty big red flag that should be brought to your doctor’s attention,” says Masi. “The threshold for concern is typically five percent of body weight over a six- to 12-month period.”

Mysterious muscle loss should be brought to your healthcare provider, “especially if combined with other symptoms like marked weakness that interferes with daily activities, balance deficits, progressive fatigue, hot and cold intolerances, nausea, vomiting, or pain,” Masi shares. “This could indicate underlying medical issues such as hormonal imbalances, malnutrition, or other diseases.”

Sabat also recommends checking in with a health professional if you experience muscle soreness that does not improve with rest, you notice any signs of hormonal imbalances (such as irregular menstrual cycles in women) or have made lifestyle changes to support your weight and muscle mass without improvement. 

The Bottom Line

Remember, maintaining muscle health requires the right combination of many factors, including adequate rest, proper nutrition, regular exercise, and stress management, says Sabat. 

“Avoid extreme approaches to diet or exercise, as they can contribute to muscle loss,” she says. “Instead, focus on sustainable lifestyle changes and listen to your body’s signals.” Muscle health (and making gains) is a marathon, not a sprint, after all.

And, again, if muscle loss is persistent or significant, consult with a healthcare professional who can rule out any underlying concerns and provide personalized guidance for your situation.