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How FAST will I LOSE my running fitness?

The first time I heard you could "lose" your running fitness was during high school cross country.

3 days.

That's all it took.

3 days.

I remember the confusion, thinking "that doesn't seem right..."

But then the panic and dread set in as everyone repeated the new mantra over and over again (so it must be true), "3 days and you start losing all your running base!"

Everything you worked so hard on during the summer: gone!

All the long runs: wasted!

All your speed: disappeared!

With this kind of fear, no wonder runners like you are terrified:

Of taking rest days

Of taking valuable time off to allow their bodies to heal

To go on vacation

To recover from a race.

What do you believe?

Have you ever gotten caught up in the fear mongering?

Or sweat a little bit when you realized life plans didn't match up with your training plan?

Ever frantically done the mental re-calculation of how early you need to get up to squeeze in a run as schedules change?

The point is: losing fitness happens without training, but it's a much more nuanced answer. It's NOT as simple as "3 days and it's all gone!"

Thank the running gods.

And actually, new research is demonstrating how detraining can actually be BENEFICIAL.

So what do you say we unpack this "detraining" and "losing fitness" myth just in time for the holidays?

Maybe you can even enjoy a couple extra days off, guilt-free?

Let's dive in!

How Long Does it Take to Lose Your Running Fitness?

As always: it depends.

"In general, significant conditioning is lost after 2-6weeks of insufficient training (Grivas)."

But let's define this:

"Detraining, defined as a partial or complete loss of training-related adaptations as a consequence of training load reduction or training cessation (Berryman)."

Humor me with one uber nerdy stat:

"Coyle et al. observed that seven endurance-trained subjects stopped training for 84 days, and their VΟ2max declined by 7 and 16% in 21 and 56 days, respectively, it thenstabilized at that level, which was still 17.3% higher than that of sedentary control subjects" (Grivas).

Did you notice a couple very key facts?

These endurance runners stopped training for 84 DAYS! And even after that, their VO2max was still 17.3% higher than their sedentary counterpart!

The reason I bring this up:

Look at how cool your body is and just how good it is at adapting and then maintaining those adaptations. Sure, without the stimuli of normal training there will be some regression in VO2max, but that's normal!

This demonstrates just how flexible and strong your body can be and how, with the right training (aka stimuli), your body can bounce right back.

It's consistent across various articles in the literature: around the 2 week mark is when detraining effects appear.

You can expect a decrease in Vo2max, however, like we talked about above, VO2max levels of active runners remain higher compared to sedentary counterparts.

"The results suggest that 2 weeks of detraining reduces cardiopulmonary functions, possibly as a result of the attenuation of hemodynamic and neuromuscular adaptations (Chen)."

"Short-term training cessation-induced performance impairment was primarily because of the loss in cardiorespiratory fitness suffered by the athletes (Garvis)."

Big science-y words, I know. But both of these blurbs actually very succinctly describe what's happening at a physiological level when it comes to detraining.

And more IMPORTANTLT, WHY you physiologically don't lose a whole ton of fitness UNTIL that 2 week mark. Let's talk about it.

What's Happening at a Physiological Level?

Science-y words mentioned above: attenuation of hemodynamic and neuromuscular adaptions.


  • a decrease in cardiovascular functions (think: blood pressure, the total volume your heart can pump out to your body, blood flow through arteries, how well your blood flows through your entire body, etc)

  • A decrease in the nerve-muscle improvements ("gains") brought on by training

Pop quiz:

Do you know WHY you have a base building block in your training plans?

It's to CREATE these physiological changes above. That cardiovascular improvement: that's from all your easy runs. And then later on in your workout training block, your long runs.

The Point:

Different runs serve as different stimuli to create a specific physiological response (isn't that cool??). And just like it takes weeks to work your way up to the point of running your 20mi long run during your marathon training program, it takes weeks to "undo" all of that work too.

Think of it this way: Construction.

On a building, road, whatever. It takes weeks to months to build this new structure. Structure is built, done; but now it sits there exposed to the elements and falls into disrepair.

Same thing happens with your body.

You don’t train for a marathon overnight. But you also don't lose ALL your fitness overnight. Your body is incredibly smart! And it will build new structures (bigger muscles, more capillary networks, more mitochondria, etc) based on the length and type of training stimuli

"When runners don’t train for a couple of weeks, the resulting drop in VO2 max is caused primarily by a loss in plasma volume, which is a key aspect of detraining." (grivas)

Key words: loss in plasma volume
Translation: a decrease in how much blood is circulating (volume)

Blood is amazing; it carries oxygen and nutrients to your muscles. It also removes waste products (lactic acid that makes you sore). It also helps humans cool off when it's 90 billion degrees outside and 100% humidity (ok, maybe not that humid).

But in responds to temperature and activity (running) your body creates more capillary networks and increases the amount of blood that’s circulating so it can send the blood closer to the skin (and still have enough blood going to muscles at the same time). All this, so you can cool off faster and more efficiently!

It makes sense then that there would be a decrease in blood volume.

"Two weeks of detraining reduces… max stroke volume…(chen)."

Translation: it takes 2 weeks for your body to figure out,"hey, we don't need ALL this blood! We're not working as hard as we were 2 weeks ago so how about we lose this extra luggage?"

Talk about efficiency.

And everything we just discussed: that's only scratching the surface of the cardiovascular system. That's not even going full depth into the neuromuscular adaptations that occur from training and detraining!

So to further put your mind at rest:

"It seems that the longer training period, the longer the detraining period needed for severe performance decrements." (Sousa)

This is why at the beginning, the answer to "how fast do I lose my running fitness" really is "it depends".

The Good Part about Detraining

Bet you didn't see this one coming?

Take a look at this quote:

"Short periods of detraining may enhance anabolic hormonal milieu and increase lean mass (Chen)."


Within context of this article, the author is saying short periods of detraining specifically of cardio-type activities can actually give the anabolic hormones (the ones that help great muscle mass) a chance to do their thing-resulting in MORE lean muscle mass.

Something you might not know: hormones run the show.

Not just for teenagers and pregnant moms.


Without hormones you don't sleep, eat, run…fill in the blank.

This isn't to say that because you run means you can't increase muscle mass.

"Nevertheless, it seems to exist a trend toward higher neuromuscular improvements when high resistance training loads were combined with low to moderate aerobic training intensities. The aerobic gains were found to be greater when higher aerobic training intensities were used, regardless of the resistance training intensities. (Sousa)"

What this is saying:

You make muscle gains by lifting heavy stuff and running at lower intensities (I'm willing to bet this includes easy runs ;) ).

And you make cardio gains by running more and harder and not focusing on lifting as heavy.

You gain what you train. It is that easy.

So when you detrain cardio, yea, you do lose some cardio fitness, but you can also make it back a lot faster compared to muscle size gains because of how hormones and physiological responses work.

(Unless you're a teenage boy. Then you just wake up one morning a foot taller with 6lbs of extra muscle. The magic of anabolic hormones and testosterone.)

The Point:

While you probably don’t want to be detraining your cardiac fitness, you can take advantage of your natural hormones.

Lift! Get strong!

Take advantage of the anabolic hormone response that gets blunted with a lot of heavy, intense running. Because research has shown, you hold onto those strength gains for up to 4 weeks if you ONLY ran for the next 4 weeks and didn't lift.

Pretty cool, right? Again, your body is smart.

So you're detraining right now: look at it as a different training block you're in. Maybe you didn't plan for it, but how can you make this problem point into a power solution?


5-7 days of Not Running: I wouldn't worry about it. Pick up in your training plan where you left off. Just observe how you're feeling and what your body is telling you during the run/workout

2 weeks: You're probably not going to want to pick up where you left off. I'd repeat either half of your last week of workouts or just repeat your previous week. (obviously, talk with your running coach about this.)

3-4 weeks: Go back and repeat the same number of weeks in your training plan as the number of weeks you took off. So if that means you rebuild your base a little bit, no big deal! You're body has already done the work 1 time, it can do it again! And probably even better than before.

How are you feeling now, runner?

Hopefully at least a little more knowledgeable and informed and amazed at how cool your body is .

Because remember, runner, your body isn't an excel spreadsheet. But we can still follow the patterns science lays out for us. And so far, your running future is looking bright.

Any other questions about detraining? Drop those below in the comment section and let's chat!

Until next time, Dare to Train Differently,

Marie Whitt, PT, DPT //

P.S. Looking for other running-type things you can do while you can't run? I've got you covered! Grab my FREE running guide here!



Berryman, N., Mujika, I., & Bosquet, L. (2020). Effects of Short-Term Concurrent Training Cessation on the Energy Cost of Running and Neuromuscular Performances in Middle-Distance Runners. Sports, 9(1), 1.

Chen, Y. T., Hsieh, Y. Y., Ho, J. Y., Lin, T. Y., & Lin, J. C. (2022). Two weeks of detraining reduces cardiopulmonary function and muscular fitness in endurance athletes. European Journal of Sport Science, 22(3), 399-406.

Grivas, G. V. (2019). The effects of detraining on cardiovascular parameters in distance runners. Med Sci Sports, 4(2), 91-95.

Sousa, A. C., Neiva, H. P., Gil, M. H., Izquierdo, M., Rodríguez-Rosell, D., Marques, M. C., & Marinho, D. A. (2020). Concurrent training and detraining: the influence of different aerobic intensities. The Journal of Strength & Conditioning Research, 34(9), 2565-2574.

75 views2 comments


Thanks Marie! I feel much better after reading this! It was like finding that last remaining present under the tree. Merry Christmas and Happy New Year!

Marie Whitt
Marie Whitt
Jan 03, 2023
Replying to

So good to hear that Paul! Hope you had a wonderful Christmas and New Year's also!

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