Sometimes working out just isn’t in the cards. Maybe you’ve been sick or have an injury. Or maybe your schedule is totally unforgiving and you’re  overloaded with work and sports.

It happens to everyone. You’d be hard pressed to find a person who has never taken some time off from training. For a few weeks, a break from exercise is not all that problematic. But de-training issues begin to arise if you extend it for too long.

Here’s how skipping workouts affects your body for the first four weeks, and for the time thereafter.

In the first four weeks . . .

Your conditioning decreases

You can quickly improve your conditioning. At the same time, your endurance is one of the first things to go after you stop working out. “You see some high level CrossFit guys who can get in great conditioning shape in a couple of weeks,” says Dr. John Rusin, a strength coach specializing in sports performance physical therapy and rehab. “You can get linearly better and linearly worse by not doing your specific energy systems work.”

Your body becomes less efficient compared to when you were training. The amount of oxygen your body can use to make energy is reduced, as is the quantity of blood in your body. This contributes to decreased aerobic endurance of up to 24 percent. Also, lactate builds up at lower intensities, so it’s impossible to exercise at the same intensity as before.

When all’s said and done, you will fatigue at a much faster rate and won’t be able to train as hard or for as long. However, this comes back quickly if you recommit to aerobic and anaerobic conditioning work.

RELATED: The Secret to Training Your Energy Systems

You will store more fat

Your body begins to use more carbohydrate, which causes two problems. First, you won’t be using fat for energy, making it more likely you will store it on your body. Second, fat is an enormous source of energy, whereas carbohydrate can deplete rather quickly if not replenished.

In addition, bad cholesterol increases, good cholesterol decreases and insulin sensitivity decreases. Insulin helps shuttle the nutrients you eat into your muscles so they can grow. Reduced insulin sensitivity makes it more difficult for this process to occur, putting your body in a situation where it can’t create new muscle.

You won’t be able to lift quite as much weight

Let’s say you can normally bench press 225 pounds for 5 reps. You take two weeks off and then can only do two reps. Obviously you got weaker, right? Well, that isn’t necessarily the case.

According to Rusin, you didn’t get weaker. Rather, your nervous system de-trained. “Really, that’s the neurological impact of not training,” he says. “You de-train yourself neurologically after as little as 72 hours.” The ability for your muscles to contract isn’t necessarily affected, but your nervous system isn’t able to tell your muscles to produce as much force. Like conditioning, this can be regained fairly quickly.

Your muscles won’t pass the mirror test

After a workout, the muscles you exercised look larger, especially if you did some muscle building work and got a serious pump. The pump effect gradually decreases over a few days, and eventually your muscles look kind of soft.

Rusin states that the pump effect fully wears off 48 to 72 hours after a workout. Muscle tone—referring to the activity of the muscle, not toned muscles in the traditional sense—decreases and the interstitial fluid and blood pumped into the muscles during the workout disperses, causing your muscles to appear smaller.

But again, it takes a long time for you to actually lose muscle size. “If you stop lifting, you’re not going to lose all of your muscle mass right away,” Rusin says. “That’s a big one that’s often misconstrued. It does take a long time to atrophy.”

You might not pass the mirror test, but if you are concerned, hasten to get a pump in and all will be good again.

RELATED: How Getting a Muscle Pump Actually Builds Muscle

After 4 weeks . . .

Conditioning decreases even further

Endurance continues to decline, with the potential to completely eliminate recent improvements. Your cardiorespiratory system become less efficient, and your heart muscles actually decrease in size after eight weeks. If you were exercising to reduce your blood pressure, these results will revert back to your pre-training numbers by 12 weeks.

Your muscles begin to decrease in size

You will see noticeable drops in muscle mass at around six to eight weeks. For endurance athletes, slow-twitch fibers essential for long-duration activity decline. For strength and power athletes, fast-twitch fibers essential for max-effort movements decrease. Across the board, your muscles simply get smaller.

You get weaker

Strength is the last thing to lose after you stop working out. It’s been found that you will lose between 7 and 12 percent of your strength after 8 to 12 weeks without training. This strength drop is attributed to decreased muscle size and continued neural de-training, as discussed above.

So what should you do?

If you have to take a break, try to limit it to six to eight weeks to avoid long-term effects that are difficult to reverse.

“I would say that six to eight weeks is kind of the make or break period,” says Rusin. “You can get a lot back within a couple of weeks. After you get out of that, you’re just going to be digging the hole deeper. It’s going to take a while to actually build yourself up higher than before.”

To limit strength losses over a major break away from the weight room, try to get at least one workout per week where you train the primary movements and do some conditioning. Even if you are injured, it’s often possible to train the non-injured side or area of your body to help maintain some of your strength.

RELATED: How to Maintain Strength and Muscle When You’re Injured

References:

Mujika, I., & Padilla, S. (2000). “Detraining: Loss of Training-Induced Physiological and Performance Adaptations. Part I.” Sports Medicine, 30(2), 79-87. doi:10.2165/00007256-200030020-00002

Mujika, I., & Padilla, S. (2000). “Detraining: Loss of Training-Induced Physiological and Performance Adaptations. Part II.” Sports Medicine, 30(3), 145-154. doi:10.2165/00007256-200030030-00001