How Long Can You Go Without Exercise Before Your Body Starts to Lose Muscle?

Are your muscles like the value of a new car — ready to start shrinking as soon as you drive off the lot (or walk out of the weight room)? Happily, no. While you will experience muscle atrophy during long periods of inactivity, there's no harm in taking a short break from working out.

Perhaps you've heard the medical buzzword sarcopenia being thrown around. Although this is a type of muscle atrophy, the word primarily refers to age-related loss of muscle mass and function.

As the authors of an article in the September-December 2014 issue of ​Clinical Cases in Mineral and Bone Metabolism​ explain, sarcopenia isn't exclusively restricted to the elderly — it can also be caused by muscle disuse or immobilization, malnutrition and inflammatory diseases.

But in general, if you're well enough to wonder about the effects of taking a week off from working out or other similar breaks, what you should actually be concerned with is the residual training effect — or how long your body will retain its exercised-induced adaptations in the absence of further stimulus.

Unfortunately, there's no single, homogeneous answer to how quickly your body detrains, or loses its training-induced adaptations such as muscular strength, endurance and speed. But the experts at ExRx.net provide a useful range of typical timelines for detraining.

When it comes to muscular endurance, you can expect the residual training effect to last around 15 to 18 days, or a little more than two weeks. After that period, if you don't continue challenging your body enough to maintain those adaptations, your endurance will start to fade. For muscular strength, the residual training effect lasts longer — about 30 days.

That lines up well with other research, although most studies about muscle loss are dedicated to "older" populations, given that muscle loss is so commonly associated with aging. For example, a small study of 12 older women, published in the October 2017 issue of the ​Journal of Exercise Rehabilitation,​ showed that a one-month detraining period was enough to reverse the gains made in a six-month strength-training program.

However, that doesn't mean you're automatically doomed if you have to take a month or more off from the gym. In another study — this time of 41 adults ages 55 to 75, published in the October 2015 issue of the ​European Review of Aging and Physical Activity ​— researchers found that after a 16-week resistance training program followed by a similar period of detraining, although the subjects lost significant amounts of strength and endurance gained during the resistance-training period, they didn't lose it all.

And an older but still noteworthy study, published in the October 2005 issue of the ​British Journal of Sports Medicine,​ suggests that high-intensity training may help you retain your exercise adaptations for longer, even after you cease training.

​Read more:​ 5 Benefits of Muscle Endurance Activity and Exercise

As the American Council on Exercise quite rightly points out, each body responds in its own unique way to exercise stimuli; so it's no surprise that your body will have a unique response to the detraining period caused by a reduction in those stimuli. But in general, taking a week off from working out won't affect your strength and endurance significantly. You can expect endurance to start fading after around two weeks, and your overall muscular strength after about a month.

But that loss is a continuum — it's not like you immediately go from the Hulk to a detrained Bruce Banner — and if you were well-trained before that period of inactivity, your muscle mass and strength may return to their previous levels, or nearly so, within just a few weeks or months of going back to training.

So if you've been knocked out of your normal training routine thanks to an injury, a busy work schedule or perhaps just lack of access to the right equipment, take heart: You might snap back to fitness quicker than you think.

​Read more:​ How to Return to the Gym After Being Sick

Even if you have been forced out of your usual gym routine, there are a few things you can do to help your body stay as fit as possible during your period of reduced activity.

If you're injured, you can often — with clearance and guidance from your health-care team — work your noninjured body parts. For example, if you have a leg injury you can use a rope-climbing machine or an arm ergometer as upper-body options for cardio, and do upper-body strength training. If the specifics of your injury permit, you can even train the healthy leg as you wait for its mate to heal.

And if you have an upper-body injury, the opposite scenario applies: You have plenty of lower-body-only options for cardio, and the saying that "every day is leg day" becomes more true than ever in the weight room. Just remember that you still need to give each muscle group a solid 48 hours of rest before you subject it to another intense strength-training workout.

What if your limitation is finding the time to work out? In that case, you can help maintain your health — and fitness — by substituting intensity for duration. Turn those long, leisurely jogs into faster-paced runs, or trade in your super-sets of single-muscle strength-training for compound exercises or power training like Olympic lifts, and you'll be done quickly — in more ways than one. Just make sure you ramp up the intensity gradually so your body has time to adapt, and always prioritize maintaining proper form.

When you do go back to training, keep in mind that even though your body may snap back quickly, it does still need time to adapt — again — to the increased stimulus. So once again, pay attention to ramping up your workout intensity, duration or frequency gradually. And if you've been sidelined to the point of serious declines in your strength or endurance, don't be shy about asking a trainer or physical therapist for help in rebuilding your capacity.

Sometimes a little expert guidance is just the trick for gracefully finding your way past the surprisingly significant mental hurdle of knowing you used to be able to do something. Even if you can't do it now, give your body an appropriate chance — and you'll be back in the game faster than you expect.