How Quickly Do You Lose Running Fitness?

Yes, a break will lead to detraining—but that doesn’t justify skipping the time off.

Taking an extended break from running—especially when there’s no outward reason, like an injury—can be hard. Occasional breaks are necessary, though, especially after a hard or long race effort. And, yes, you will lose fitness during those few weeks off. 

A loss of cardiovascular fitness and endurance starts to happen after as little as 12 days of no exercise, a 2020 literature review published in Frontiers in Physiology found. When runners who participated in the 2016 Boston Marathon then cut back on their exercise post-race, dropping from about 32 miles per week to three or four miles per week, their cardio fitness dropped significantly, according to a 2018 study published in the Journal of Applied Physiology. And adults who took a month off after following a regular cardio routine for four straight months lost almost all their aerobic gains in that month, according to earlier research published in Nutrition, Metabolism and Cardiovascular Diseases.

Strength sticks around a little longer. During a training hiatus, your body can maintain strength for up to three weeks, one older analysis in Sports Medicine found. (If you’re completely sedentary, you might lose strength faster.)

Here’s the thing, though: If you just finished a big race, you need that break. It can take up to four weeks for your body to fully recover physiologically from “massive aerobic exercise,” according to older research published in Free Radical Biology and Medicine.

Thanks to social media, there can be this insidious pressure to bounce right back from a big physical undertaking. If everyone else can keep grinding, why shouldn’t you? But this persistent “no days off” narrative is outdated and harmful—and it applies not just to run streakers, but those who don’t give their body proper recovery time. 

Exercise is a stressor. It breaks your body down in the moment, and the growth phase—the gains—don’t happen until you stop exercising and allow your body to adapt to that stress. That adaptation process is how you’re eventually able to run further or faster.

But training isn’t a relentlessly upward diagonal; the line should go up, then briefly down, then up again, and so on. That’s why we taper before a race, why we include deload or down weeks throughout a training cycle—reducing your training volume helps you avoid overtraining injury by allowing your body to repair damaged tissue, and it can also help stave off the mental burnout that can come with nonstop hard training.

It doesn’t matter how fit or fast you are, it’s just not possible to maintain peak fitness at all times; in order to keep pushing that upward trajectory, you have to incorporate some down time. If you push things too soon, chances are, that first run back won’t feel awful because you lost fitness—it’ll feel awful because your body still hasn't recovered. 

All that said, any fitness you do lose will come back quickly once you start training again. You don’t lose the long-term gains and the huge aerobic base that you get from months of training in just a couple of weeks. Athletes reached their peak fitness levels more quickly after a break than when they first began training, older research published in PNAS determined. 

Another much older study from the Journal of Applied Physiology suggests that runners begin to lose their fitness after 48 to 72 hours, and that it takes two days of retraining to regain the fitness lost for every single day of training skipped. Those numbers may sound scary, but let’s say you take two weeks off post-marathon—that would translate to four weeks until you’re back to your previous fitness level. In a zoomed-out look at the bigger training picture, that’s no time at all.

From a strength perspective, your muscles actually store memory on a molecular level from past resistance-training sessions for up to 20 weeks, a recent study published in the journal Medicine & Science in Sports & Exercise found.

With running, what you’re losing is mostly aerobic conditioning, and you can maintain that—and reduce the effects of detraining—with other activities. Taking time off from running doesn’t mean stopping all exercise, which sounds like a no-brainer but is a surprisingly common misconception. 

Recovery can include low-intensity aerobic work—cross training on a bike or in a pool can help you maintain your aerobic fitness without putting too much stress on your body, while restorative and mobility-minded workouts can help loosen up your muscles. When you’re ready to get back into running, following a reverse taper can help you safely return to your normal base volume. 

And if you can’t fathom taking more than a couple of days off of running after a big physical feat, it might be time to question why.Relying too heavily on running or using it as your sole coping mechanism for dealing with stress is a guaranteed way to set yourself up for overuse injuries, body image issues, and disordered thinking. Sometimes, taking a step back is what you need—physically and mentally.

the rundown

Adidas Adios Boston 12
I so want to like this shoe, especially since the latest iteration—continuing what the Boston 11 started—looks so much sleeker than previous versions. It’s much closer in style to the race-ready  Adios Pro 3, which makes it a great training counterpart. What’s changed is that Adidas added more Lightstrike Pro in the forefoot, a softer Lightstrike Pro 2.0 in heel, and reimagined the one-piece mesh upper and the EnergyRod configuration. Unfortunately, it still doesn’t do it for me. I’d liken it to the Nike Pegasus—a workhorse, but one that can feel a little flat and unresponsive. I know plenty of runners who do love this shoe, so if you’ve liked past models, you’ll probably like this one, too!

“Worn” PEBA Foam Increases Energy Costs of Running—Eventually
There’s been a lot of talk lately about “single-use” racing shoes, and I know plenty of runners who have been loath to wear their race day marathon shoes in a second race. But shoes with advanced footwear technology last longer than you think. After 279 miles, PEBA foam—a common super shoe material—did increase energetic costs in trained runners, while traditional EVA foam did not, a new study published in Scandinavian Journal of Medicine & Science in Sports found. A midsole with PEBA foam will experience greater wear and worsen running economy over those nearly 300 miles, but 300 miles is a lot of time in a shoe—so, yes, you can likely get a second (or even third!) race out of those Alphaflys before you relegate them to training miles only.

Therabody Theragun Sense 
Therabody just released the Theragun Sense, which is the first massage gun from the brand to combine percussive therapy with calming breathwork to ease pain and promote mindfulness. The massage aspect is as you’d expect, but I was intrigued by how a device like this would promote stress management. Basically, you hold your finger over the built-in biometric sensor and cradle the device to your chest (yes, it’s awkward) and follow the breathing routines that are pre-loaded to the device or beamed in via Bluetooth from the app. There’s no real-time heart rate display, but you will see your heart rate at the end of a session; mine dropped from 69 beats per minute (per my Apple Watch) to 42 over the course of two minutes. Even if you’re not swayed by the biometric feature, you can get some similar features (and power) to the Pro at a more affordable price.

Meet the Marathon Cheats
I will never not be fascinated by people who cheat in endurance races. This older story (but new to me) from The Guardian looks at the course cutters, bib mules, and straight-up liars in the running world. Some are motivated by a race’s prize money or even just the medal, some are trying to obtain qualifying times for the Boston Marathon, and some are just doing it for bragging rights on social media. I find it especially mind-boggling that people who cheat in the social media era, when everything is documented and tracking apps and chips make it nearly impossible to get away with it. And good luck to those who try, because you’ll likely end up on Marathon Investigation, a blog that exposes cheaters in the marathon world.

“Brittany Dawn,” Maintenance Phase Podcast
Speaking of cheats! This Maintenance Phase podcast was a wild ride from fitness influencing (I also learned a lot about the Christian fitness niche). I knew of Brittany Dawn as a fitness influencer/grifter who sued by the state of Texas for charging followers hundreds of dollars for “customized” plans that were not, in fact, customized (she eventually settled out of court). But there are a couple salient points amidst the drama: 1) It’s so, so important to vet who you receive health advice from, because there are lots of people out there monetizing their personal journey with no certifications or education to back up their advice, and 2) be wary of those who share inspirational, educational messages that don’t jive with the photos they post (i.e. “love every part of your body!” with a Photoshopped photo that shows no imperfections). If the messenger and the message don’t match, that’s a red flag.