How Long Does It Take to Lose Running Fitness?

If you follow me on Instagram, then you know—I’ve been forced to take a lot of unplanned breaks over the past year and a half. And I constantly find myself asking the question: how long does it take to lose running fitness?

Subsequently, I’ve had a lot of mother runners ask me that same question when forced to take time off due to injury, illness, or LIFE.

For me, I had to take 4 months completely off in 2020 due to my hamstring tear and resulting high hamstring tendinosis. Then for almost another year, I rode the waves of gains and losses as I figured out what my hamstring could tolerate.

Related: Lessons Learned from My Running Injury

This year, I was finally back and healthy, only to get pleurisy (inflammation of the lung lining) after second COVID-19 vaccine, forcing me to take several weeks off when I was finally in race shape.

How long does it take to lose running gains?

How long does it take to lose running fitness?
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It is so hard not to freak out and worry about all the fitness we’re losing when we aren’t pounding the pavement or hitting the track. But take heart. Science shows that all the time and effort you put into your running fitness isn’t lost in a day or even weeks.

In short, it takes about TWO WEEKS of doing completely nothing for fitness to decrease by a statistically significant amount.

Just as it takes time to build, it takes time to lose. Our bodies work in long time scales in both directions.

Famed running coach Jack Daniels (whose program I became a certified coach under) takes into account all the physiological variables that go into losing running fitness (including VO2 max, lactate threshold, speed, and running economy).

According to Daniels, this is how long it takes a runner to lose running fitness:

0-5 days off running: no change

7 days off running: 0.6% change

14 days off running: 2.7% change

28 days off running: 6.9% change

72 days off running: A runner is almost completely detrained.

Is it okay to take a week off running?

Yes, it is okay to take a week off running. In fact, it is recommended by Daniels to detrain after each training cycle for about two weeks to allow your body to return to homeostasis, build itself back up again, replenish stores, and give you a mental boost. In fact, the coaching great views a planned break as part of the training cycle itself.

Still, if you’re forced to take an unplanned break in the middle of a training cycle, do not despair. Research shows that you will not lose your fitness quickly.

Key takeaways from the research show that:

  • It takes about two weeks of total rest to lose any statistically significant amount of fitness.
  • Current fitness is easily maintained with even just a couple sessions a week.
  • The fitter you are, the easier it is to get your fitness back.
  • Still, the first couple runs back will feel rough as your body adapts.
  • It’s important to start back gradually (easy mileage with strides) before resuming training.

Here’s what the research says about how long it takes to lose your running fitness:

4 Truths of How Long It Takes to Lose Fitness 

Your body does go through metabolic changes when you detrain.

Let’s get to the bad news first.

When you take time off, adaptations do happen in the body that make your use of energy less efficient, thereby leading to slower running and more discomfort.

A 2000 study in the journal Sports Medicine, followed athletes who didn’t exercise much over 4 weeks. After about one week of inactivity, they started to notice the following changes:

  • a reduction in capillary density and oxidative enzymes which impacts how much oxygen your body can process;
  • along with a rise in how much oxygen a person then consumes over carbon dioxide produced;
  • a decrease in glycogen uptake and an increase in fat-burning (which leads to slower running); and
  • an increase in fast-twitch muscle fibers over the use of slow-twitch muscle fibers, leading to a faster accumulation of lactate leaving your legs burning and heavy.
  • Additionally, other factors outside this study such as a decrease in muscle tension and neuromuscular changes can lead to a decline in running performance.
  • A 1985 study in the Journal of Applied Physiology found a 9 percent reduction in blood volume and a 12 percent reduction in stroke volume after two to four weeks of inactivity in trained men. This impacts your VO2 max, making running feel hard.

Overall, after more than a week off, your running economy decreases short-term as the nervous and biomechanical systems get less efficient.

But don’t drown your sorrows in a jar of peanut butter yet—I mean, for goodness sake, eat the peanut butter but don’t cry over it! There’s good news!

It’s easier to regain fitness after you’ve lost it.

Yes, while you may have a small decrease in aerobic fitness, speed, and running economy, your fitness remains at the surface. Thus, it takes less time to get it back than it did to get it in the first place. 

As Daniels writes in his iconic book Daniels’ Running Formula, “it’s easier to regain a level of fitness than it is to attain it in the first place. You’ve been there before, so experience is on your side.”

Those biological changes (such as neuromuscular efficiency and capillary and mitochondrial density) you worked so hard for don’t completely reverse as soon as you stop hitting the pavement.

According to Daniels’, it takes about about two and a half months of detraining (or complete inactivity) for you to reverse the biological adaptations of your training. Also, some studies show there is a sharp decline around two weeks of detraining which progresses for about two months, but then the decline slows.

Plus, there’s this:

The fitter you are, the easier it is to bounce back.

This 1991 study in the Medicine and Science in Sports and Exercise and this 2015 study in the European Journal of Applied Physiology find it’s easy to regain your fitness after you’ve lost it.

This goes back to all the changes within your body that you’ve triggered with your hard work. It’s become super energy-efficient. Additionally, the nuclei in your muscles remain intact, finds a 2019 review in the Frontiers of Physiology. Thus, it just takes a bit of time to reactivate them. (More on how to do that is below.)

It’s easy to maintain current fitness.

A lot of these studies that show a decline in fitness study participants who do zero cross-training or aerobic conditioning. (Cross-training does slow the rate of which you detrain!). Thus, it’s easy to believe it’s all doom and gloom when sidelined.

But take heart.

Studies, like this 2021 article in the Journal of Strength and Conditioning Research, have found that endurance performance can be maintained for 15 weeks on as little as two sessions per week, or a reduction in volume of up to 66 percent with sessions as short as 13 minutes!

In general, volume and frequency can be more than halved as long as there is some intensity in the workouts. Reintroduce volume and intensity, and you’re back where you started after just a couple of weeks!

For VO2 max in particular, a 1985 study in the Journal of Applied Physiology had athletes cut training volume from six to ten hours a week to just one 35-minute session. Amazingly, those athletes had no reduction in their VO2 max.

However, their performance did decrease likely due to the physiological changes noted earlier in this article.  

How should I return to running after time off?

How to return to running after a break?
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Even if you haven’t taken more than a week or two off from running, expect your first couple runs to feel difficult. That’s because you still have experience some of those metabolic changes such as a slight reduction in your VO2 max or a switch to fast-twitch muscle usage.

Remember that your fitness is still there. It is a sleeping giant underneath the surface. It will take a couple of easy runs with sprinkles of faster running to wake it up.

Because of this, even if you’ve been off running for less than 5 days, do not jump right back into training, warns The Mother Runners Co-coach Laura Norris.

Based on Daniels’ formula, here is guidance on how to return to running after a break:

Return to Running Plan

0-5 days off running: Easy running at 100 percent volume equal to number of days off with strides

6 days off: 3 days easy running at 50 percent volume; then 3 days easy running at 75 percent volume with strides

28 days off: 14 days easy running at 50 percent volume; then 14 days easy running at 75 percent volume

29+ days off: 9 days easy running at 33 percent volume; 10 days easy running at 50 percent volume; then 10 days at 75 percent volume with strides

8 weeks off running: 18 days easy running at 33 percent volume; 19 days easy running at 50 percent volume; then 19 days at 75 percent volume with strides

 8+ weeks off running: 3 weeks each at 33 percent, 50 percent, 70 percent, 85 percent, 100 percent with strides.

72 days off running: A runner is almost completely detrained.

Because there are variations in the reasons you took time off (bone versus soft tissue injury, a bad cold versus COVID-19), there are different guidelines for your return. View Coach Laura’s sample return to running plans here.

Related: Expert Tips to Diagnose, Prevent, & Treat Running Injuries

Unplanned breaks can end up giving you fitness gains

In a fantastic 2021 Trail Runner Magazine article by amazing running coach David Roche of Some Work, All Play Running, Roche points out that many breakthroughs come from breaks. Why? Because these breaks can allow your body to recover and build back up again before resuming training.

If you play your cards right, breaks can lead to exponential growth processes that reset what you could have ever thought possible before the layoff,” writes Roche. “A few days on your butt could heal muscles, balance hormonal fluctuations from hard training and stoke the motivation fire. After a short time off, you may even be stronger than you were in ancient times (a few days prior) when you were able to run.”

If you’re off due to injury or illness, I’m sharing what my coach Bobby Holcombe of Knoxville Endurance told me: “You will drive yourself nuts trying to analyze where your current fitness is. Just make sure you focus on rehabbing the current things that are distracting us from training full-time.”

Running constantly forces us to be in the moment—even when not running. Take the time to heal with peace knowing that any fitness you lose will come back fast, and you will be stronger in body and mind when you do.


PS-I’d love to help you reach your running goals whether it be to run your first 5k or run competitively! Email me at with questions or check out my Coaching Services page!

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