Here's How Rapidly You Start to Lose Muscle Once You Stop Lifting Weights

Unsplash | Victor Freitas

If you think taking a break from working out doesn't make a clear difference in your strength, you're wrong. My first gym session after a trip to Barcelona, where the only exercise I did was walking (and eating paella), was a struggle. The barbell I used to pick up with ease suddenly felt way heavier. (I actually triple checked to make sure I hadn't accidentally grabbed the wrong barbell — nope.) You may know the feeling. Returning to the gym after an extended break can be brutal.

"Unfortunately, exercise is truly 'use it or lose it.' If you stop strength training, you'll likely notice decreased strength (making it harder to perform daily activities), energy loss, impaired balance, and weight gain in as little as 3-4 weeks," Meghan Nagel, manager of fitness programming at Virtual Health Partners, told POPSUGAR. "Your muscles may also feel less firm and 'toned' when you stop lifting." (That sound you hear is me screaming "whyyyyy?" into the weight room abyss.)

To find out what happens to your body when you stop strength training, POPSUGAR spoke to Nagel and Dr. Jacqueline Schaffer, board-certified MD, bestselling author of Irresistible You, and founder of Schique Skincare. Here's what they had to say.

You Lose Strength
POPSUGAR Photography | Rima Brindamour

You Lose Strength

Obviously if you don't work your muscles, you will lose strength, but the rate at which you do so is kind of upsetting. "Researchers have found that you lose strength at about half the rate you gain it. In other words, if you increased your arm strength by 20 percent in four weeks, you would lose 10 percent of that strength within four weeks and all of your strength gain within eight weeks," said Nagel. "Many people notice a loss of muscle size and definition within 3-4 weeks. However, how fast you lose muscle mass depends on a variety of factors, including age, gender, and fitness level," she added.

Basically, your strength decreases due to a combo of things, including lack of blood flow, a decrease in capillary size, and a decrease in muscle mass, explained Schaffer. "On a micro level, your muscle fibers are not being used and don't need to store glycogen for energy. The lack of nutrients for your muscle fibers causes them to atrophy. This atrophy leads to strength reduction," she explained.

Your Metabolism Slows
POPSUGAR Photography | Kathryna Hancock

Your Metabolism Slows

When you strength train, you build muscle. Muscle actually increases your metabolism, helping you burn more calories throughout the day. But when your muscle mass decreases, explained Schaffer, your metabolism begins to slow down. (You may notice this around week five, she said.)

How Long Does It Take to Get It Back?
POPSUGAR Photography | Sheila Gim

How Long Does It Take to Get It Back?

It takes around 21 days to get your groove back, said Schaffer. That's because the amount of oxygen that can be used in an intense exercise (VO2) has decreased, and "your slow and fast twitch muscle fibers are not as dense and strong as they used to be."

"You'll probably feel weaker and less energetic after a long hiatus from the gym, so start slowly, using lighter weights and more repetitions. Concentrate on proper form, and stick to basic exercises," said Nagel. In other words, don't go into the gym and try to PR on your deadlift. Take your time to build up the weight you use, no matter how frustrating it can be to lift lighter than usual. (Trust, you do not want to injure yourself — then you'll be out of the game even longer.)

The good news from all of this: a few days off your strength routine isn't going to seriously mess up your training. So stop feeling guilty about taking a day off here and there. And if you're worried that skipping a workout will result in a collapse of your entire exercise routine, here's why you shouldn't be.