How Long Does It Take to Lose Muscle?

While not ideal, many of us have to pause our workout routines from time to time. Whether you’re stressed, sick, injured, going on vacation or just need a break, there are plenty of reasons to take time off from exercise.

But, no matter how badly you need the break, you may worry about losing all your hard-earned muscle before you’re ready to start training again.

If you don’t train at all, you may start losing muscle mass after 72 hours, says Michele Olson, PhD, a professor of exercise science at Auburn University in Montgomery, Alabama. Even your heart, which is also a muscle, will show a decrease in the amount of blood it can pump per beat after 72 hours off from exercise.

You’ll notice the effects on your heart a lot sooner than your biceps or quads. “If you work out on Monday and miss three days, returning to a workout on Friday, you will feel a bit more breathless than typical, because less oxygenated blood is being sent out from the heart per beat,” Olson says. “It’s not training-breaking, but it can be noticeable.”

Although you start losing muscle mass after 72 hours, you probably won’t notice any losses until you’ve gone 3–4 weeks without training. One small study found that trained men could take three weeks off from exercise without any noticeable muscle loss.

However, there are a few factors that determine how quickly you lose muscle mass, including:

The longer you’ve been lifting, and the more muscle you have, the better off you’ll be if you decide — or have — to pause your routine. “If you’re fit with developed muscles, you will still have a baseline of muscle that others will not have after a period of inactivity,” Olson says.

Adequate protein, in particular, is key for building and maintaining muscle mass. If you skimp on it, your body won’t have enough amino acids (the building blocks of protein) to keep up with the constant breakdown and rebuilding of cells (muscle, red blood, hormones, etc.) that goes on all day, every day. Eventually, your body pulls from your muscle stores to get the amino acids it needs to keep your other cells and tissues functioning. The result? Muscle loss.

For example, in one study, sedentary to moderately active elderly women who ate a low-protein diet (1.47 grams of protein per kilogram of body weight per day) lost roughly 14% of their muscle mass after nine weeks. (However, it’s worth noting this amount of protein falls within the range of 1.2–2 grams of protein per kilogram of body weight per day recommended for older adults.)

So, even if you’re not training, you need to make sure you’re getting enough protein to prevent muscle loss.

Protein needs vary from one person to the next, but as a general guideline, the International Society of Sports Nutrition suggests active people aim for an overall daily protein intake between 1.4–2 grams per kilogram of body weight (older adults may need to aim for the higher end of the spectrum). To put that in numbers, a 150-pound active person needs roughly 95–136 grams of protein per day.

Many age-related changes can make it harder to build and hold onto muscle. One of those changes relates to the nervous system.

As we age, we begin to lose motor neurons. Studies suggest there’s a drastic decrease between ages 60–70. Motor neurons transmit impulses from the spinal cord that tell our muscles to contract. When you lose motor neurons, it becomes harder to recruit muscle fibers, Olson says. If you can’t recruit muscle fibers, the fibers won’t break down and rebuild to grow back bigger and stronger.

Strength training can help reverse these changes to the nervous system — and other age-related changes — but once you stop training, the benefits gradually disappear.

Males have a slight advantage when it comes to muscle. “Men have more natural testosterone, which is anabolic to muscle tissue development and maintenance,” Olson says. (Anabolic refers to the process of building larger molecules out of smaller molecules, like building protein out of amino acids.)

How quickly you’ll lose muscle once you stop training depends on different factors, but in general, you’ll notice losses in 3–4 weeks.

If you have to cut back on exercise for whatever reason, and you don’t want to lose any hard-earned muscle, you may be able to get away with doing only two strength workouts per week, according to Olson. Target every major muscle group (back, chest, shoulders, biceps, triceps, quads, hamstrings, glutes and calves), and do at least 1–2 sets of 8–12 reps per exercise.

But even if you can’t — or don’t want to — train for a few weeks, you won’t have to go back to square one once you restart your routine. So long as you’ve been training consistently up until your break, you should be able to rebuild muscle and strength fairly quickly.

Whether you want to run your first mile or set a PR, having a plan gets you there faster. Go to the MapMyRun app, tap “Training Plans” — you’ll get a schedule and coaching tips to help you crush it.