TIf two recent studies out of the University of Liverpool and McMaster University are true, then that old saying, “If you don’t use it, you’ll lose it” can even be taken a bit further: “If you don’t use it, not only will you lose it, but you might not even get it back!”

The studies monitored regularly active and healthy people without Type 2 diabetes, who stopped working out and sat around for a couple weeks and discovered that their health markers worsened in just a couple weeks.

Specifically, their blood sugar levels rose, their insulin sensitivity became worse and they gained weight. What’s even scarier is that when some of them—especially the older participants—returned to their regular exercise programs, the negative metabolic changes that had occurred in their bodies during those two sedentary weeks didn’t fully reverse themselves.

Here are links to the two studies:

Study 1(https://www.ncbi.nlm.nih.gov/pubmed/29671031)

Study 2 (https://www.ncbi.nlm.nih.gov/pubmed/29095970)

The magic number seems to be two weeks, especially in people 65 years old and older; they had a harder time reversing the damage placed on their bodies from those two lazy weeks. However, even past studies that looked at college-aged people showed a similar result; health markers decreased in just two weeks, but their young age allowed them to reverse the damage quite quickly.

Don’t be fooled: This isn’t an excuse to not take a rest day. Rest days are crucial for your recovery. We don’t want to see you here seven days a week, but it’s certainly reason to not less yourself fall off for more than a few days at a time, and reason to continue to exercise even on your 3-week vacation this summer!

The fine line between taking much-needed rest days and losing fitness…

Sometimes your body needs more than a day off. I know when I have taken a week off here and there, I feel like I come back stronger and mentally fresh, ready to attack training again.

According to previous research, one of the first things you start to lose is your cardiovascular fitness. For a conditioned runner, for example, it might take 7 to 14 days until they start losing their aerobic capacity.

In this article, an exercise physiologist explains that a person’s V02 max (essentially how efficiently your body uses oxygen) will start to decrease after just two weeks, as well as your lactate threshold (the intensity point where your blood concentration of lactic acid starts to increase exponentially).

Also consistent with the two new studies from Liverpool and McMaster that I noted above, older people lose their endurance faster than younger people.

Strength loss is pretty similar, as it typically takes just two weeks of not using your lower body for you to lose one third of your muscular strength.

That being said, you might feel a little weak for a day or two if you don’t squat for two weeks, but this isn’t necessarily a negative thing. That strength will easily return as fast as you lost it.

The lesson: Your body needs rest to recover, but two weeks of doing nothing is likely too much!

Alas, our prescription for you:

• Show up to the gym three to five days a week as much as possible (On top of this, we strongly encourage you do get outside and hike, ski, run, swim, bike, surf, golf etc. once a week when you can, and try a new sport each year).

• Listen to your body: If it tells you to take a rest day, take it. Even if it doesn’t, take at least one rest day per week.  

• One or two times a year, take a full week off (or at least of an active recovery week, where you’re away from the gym), to heal any nagging injuries and reset your body and your mind.

• Avoid taking two weeks or more of sedentary living!

Obviously everyone is different, however, the above template is what we think is best for most people, to allow them to live a long, happy, fulfilling and independent life.