John Davis

Written by John Davis


How Long Does It Take to Lose Your Running Fitness?

Whether it’s taking time off from running due to injury, taking a break to recover after a marathon, or a hectic life just getting in the way, we as runners are not great at missing training.

Sometimes we wonder if it is even okay to take a day off running when we have pain!

Not only does it remove one of the more enjoyable daily activities from your schedule, but there’s also the concern of losing fitness.

Most runners know it is important to take time off from running at the end of a season, and every runner who has spent any time injured has worried about losing their fitness while their body heals.

Or are we the only ones?

Thought not!

Today we will cover just how fast you lose aerobic fitness when you have to stop running. Hopefully it can put your mind at ease the next time you have to take a break.

Injury, recovery after a marathon, a hectic life. If we can't run for a few weeks, do we lose all our running fitness? Not as much as you think! Here is what the science says about how quickly you lose your strength and endurance when you have to stop running.

Fortunately, as aerobic capacity and endurance are fairly easily to measure, there are some strong studies that give a good picture of the decline in fitness during time away from running.

Additionally, they also offer some insight into why you lose fitness, and from this we can help you with how to safely return to running…..without ending up back on the bench with another injury!

How Quickly Will Taking Time Off From Running Hurt Me?

One study conducted by Elizabeth Ready and Arthur Quinney, looked at the rise and fall in aerobic conditioning in a group of men who followed a cycling training program for nine weeks, then rested for nine weeks (detraining).

The twelve men in the experimental group rode hard for 30min four times a week for nine weeks, while the nine men in the control group remained sedentary.

All 21 men had their VO2 max and anaerobic threshold tested before the study and every three weeks afterwards for eighteen weeks (during the nine-week training intervention and for nine weeks of detraining).

Not surprisingly, the trained group improved their aerobic conditioning significantly during the study: their VO2 max increased by 40%, and their anaerobic threshold increased by 70%.

Check this out:

Interestingly, the control group had a slight increase in fitness too—perhaps because they were supplementing their sedentary lifestyle with a maximal aerobic test every three weeks!

After training ceased, anaerobic threshold and VO2 max dropped fairly rapidly.

After the first three weeks of “detraining,” the subjects’ anaerobic threshold had already dropped by almost 20%.

But don’t panic just yet:

The rate of decrease leveled off.

Even after nine weeks of (almost) no activity, the cyclists retained about 40% of their gain in fitness over their previous sedentary life.

However, Ready and Quinney did not use trained athletes, so it’s possible that the effects of detraining will be different in a trained athlete vs. a newly-trained one.

How quickly do you lose fitness when not able to run?

Edward Coyle et al. conducted a study on the topic of detraining in already-fit athletes.

Using seven endurance athletes with many years of training experience, Coyle et al. established baseline fitness levels, and measured how their fitness declined after 12, 21, 56, and 84 days off (for a total of twelve weeks).


The initial dropoff in fitness was fairly quick: after 12 days, levels of enzymes in the blood associated with endurance performance had decreased by 50%, and VO2 max had dropped by 7%.

But the reduction in fitness leveled out over the following weeks; the final level of the subjects’ VO2 max was still only 18% lower than when they’d begun.

Want the good news?

Some factors, like capillary density—the number of small blood vessels that grow deep into the muscles—did not seem to be affected at all by detraining.

These results suggest that trained athletes lose less fitness than sedentary people who have only recently started exercising.

If you rest after a marathon, what happens to running fitness?

A third study at Odense University in Denmark looked at practical implications of time away from training.

Klavs Madsen and colleagues used nine endurance athletes who regularly trained for eight hours per week.

Madsen et al. studied the effect of a four-week break from training with a ride-to-exhaustion on a stationary bike before and after the time off.

Though the study did not detect any statistically significant change in VO2 max, the subjects’ were able to cycle at 75% of VO2 max  for 80 minutes before the study, and just over 60min after the study—a 20% decrease.

This is more relevant to runners in training, as it’s a closer approximation to preparing for a big race, followed by time off running to recover, like taking a week off after a marathon.

Peripheral factors in the muscles, including calcium and magnesium concentrations, and muscle glycogen storage, affected the body’s ability to exercise more than the core cardiovascular “engine.”

What’s the bottom line?
Nevertheless, a 20% change in a ride to exhaustion is fairly significant, so the effects of a month off training are going to have a big impact on performance.

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If I stop running for a few weeks, will I lose all my endurance and strength?

Combining the data from the studies results in good and bad news for runners who have to take time off.

Initial declines in fitness occur rapidly: There are measurable declines in fitness, and enzyme levels associated with performance drop by half in under two weeks.


These declines level off after several weeks of inactivity.

What if I have to take a lot of time off?

If you’ve been training for a long time, your “lifetime” aerobic conditioning is still mostly intact; long term gains in fitness are only minimally affected by time away from running.

You are likely to lose a larger portion of the more immediate gains of training: enzyme levels, glycogen storage, and muscular efficiency.

What does that mean?

Your more recent improvements are severely affected by time off.

There are few studies that have analyzed longer than three months away from activity, but an 80% retention of fitness after 12 weeks of inactivity in the Madsen study is a good sign.

How long does it take to regain fitness after time off running?

The results from Ready and Quinnely also suggest that it won’t take as long as you think to get back to your initial fitness.

Over nine weeks of training, the subjects increased their anaerobic threshold by 70%, but after nine weeks of inactivity, they had retained 40% of the initial increase.

It would not take them another nine weeks to get back to peak fitness level.

What’s the bottom line?

If you are taking some time away from running, realize that you will lose a significant portion of your fitness, and you will lose it fairly quickly, but your losses will taper off after several weeks, and you retain a portion of your initial fitness levels for a long time.

Is there anything to prevent fitness loss during time off running?

Cross-training is one way to hold off the initial drop in fitness.

Studies on aqua jogging suggest that you can maintain your conditioning for at least six weeks with a rigorous program.

But even if you don’t cross train, take comfort in knowing that your hard work is not lost, and that it won’t take nearly as much time or effort to regain your fitness level as it took to get there initially.

You can also read our study on Racing Well off Cross Training- Even if you are injured and listen to our podcast on cross training to get more reassurance that you can stay in shape through cross training.

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1. Ready, E. A.; Quinney, H. A., Alterations in anaerobic threshold as the result of endurance training and detraining. Medicine & Science in Sports & Exercise 1982, 14 (4), 292-296.
2. Coyle, E. F.; Martin, W. H.; Sinacore, D. R.; Joyner, M. J.; Hagberg, J. M.; Holloszy, J. O., Time course of loss of adaptations after stopping prolonged intense endurance training. Journal of Applied Physiology 1984, 57 (6), 1857-1864.
3. Madsen, K.; Pedersen, P. K.; Djurhuus, M. S.; Klitgaard, N. A., Effects of detraining on endurance capacity and metabolic changes during prolonged exhaustive exercise. Journal of Applied Physiology 1993, (75), 1444-1451.

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23 Responses on “How Long Does It Take to Lose Your Running Fitness?

  1. I’m up this morning for my first run in three weeks. Unfortunately my level of running had been dropping off for almost a year and I’m coming back permanently disabled with Graves disease. I expect it will hurt some and I’m not sure my heart and lungs are even operating well enough to be conditioned. But the longer I wait, the harder it will be.

    • Hi Nielsen, how are you getting on? At least you can rest assured that your base fitness levels will still be there from your years of training prior. If we can help with any articles, please let us know.

      • I was perfectly fine and training was going well until
        I got sick for 2 months. I had to take April, May and some of June off. Now for the 5 k, I’m 2 minutes slower than what I was in April even though I’ve been back to training. Lucky Cait. I’m glad she bounced back quickly but I’m opposite, sadly.

  2. Hi Nielsen
    I too have graves!! Initially I didn’t know what was wrong. Running was so hard I had to stop and my heartrate was horrendous. Anyway I’m on the carbimazole now and back running until I got injured! Just wondered how you are getting on now as I see you posted back in August. Are you still running?

  3. I have Graves’, though I’ve been in remission for 3 years and certainly don’t consider myself permanently disabled! I wouldn’t advise strenuous exercise whilst hyperthyroid, however – your body, particularly your heart, is under enough strain as it is. Wait until your thyroid hormone levels are within the normal range.

  4. (I should add – I now run 3 to 4 times a week and cross train on the other days. Nothing to do with the Graves’, I just tend to get injured if I run more frequently than that)

    • Hi Emma, great to hear you are in remission! Thanks for the advice, I am sure others in a similar position will find it very helpful. Running 3-4 times per week is plenty to maintain fitness, especially if you are injury prone. It is good that you are able to listen to your body, and do what you need to do to stay healthy. What kind of cross training do you do?

  5. Hello,

    I have good running fitness, I’ve trained that well over a couple years. But now I decided to add some more muscle mass, that means much more resistance training and nearly no explicit cardio workouts. However, my resistance workout pace is fairly high such that my heart rate is somewhat high (of course not as much as running but fairly high). I also do rigorous Ashatanga yoga workout once a week. The question is, will this workout plan would decrease my running fitness or not?

    • Hi Hesham, are you still keeping up with your running in any way? That is the only way you are truly going to keep your running fitness up, as your body needs to be used to the pounding. The yoga and resistance training will be supplemental activities to your fitness, and will most likely help, but you are only going to maintain that cardiovascular fitness through running itself, or running simulated activities such as pool running or using an elliptical. You will probably find it will come back quicker than you expect when you do increase your running again 🙂

  6. Hi, I have a fitness test for a club I want to join that needs me to get 9.10 on the bleep test. I passed a practice on the 9th of December fairly comfortably but due to travelling home and coursework have missed running for about 10 days. How much fitness will I have lost? and if I have lost a lot what is the best way to catch it back up? My real test is on the 4th of Jan and I am so stressed right now…


  7. Taking a week off every now and then fro all exercise being cardio. (running, biking, etc..) and strength training I experience minimal declines. Some weeks I have less decline and some weeks more. Strength training I experience minimL if any, decline. As for cardio. fitness I do experience a slight decline. I usually do a combo. of both running and cycling alternating between the 2. I experience the most decline in running fitness.

    I ran my 1st err 5k Oct 4th, 2014 after 10 day off running only biking some of those days. I got a time of just over 22 min.The course was totally flat. Makes no sense other then it ws my 1st 5k and I had adrenaline going with me. T this da I can’t beat that time. I even ran a 5k the next day and got a time of 23:30 approx.
    which is my average 5k time. not bad at all for running back to back 5k’s (!st 2 ever) with good times. I have been running over a year before this. Both races I pushed myself.

    • Exactly Kurt, it is a shame more people do not have the confidence to be able to take a week off to completely recover more often. Thanks for sharing, that is interesting, but not really surprising as sometimes this is all our bodies need. Keep up the good work, and keep us informed on how you are doing!

  8. I’ve been walking jogging 2-3 miles in 30-45 minutes 4 times per week for the past 17 weeks. I haven’t walked at all this entire week due to illness. Will I be able to resume my normal level of activity after a whole week off, or will I need to ease back in?

    • Hi Kathy, you should go easy for the first week back, just walking/running a little slower than you usually would to make sure you feel okay, but you should not take very long at all. It is better to be safe than sorry 🙂

  9. Hi I am 71 and love running but have a perennial longus injury and already been out 4 weeks and so worried when hopefully I get back ruining I would have lost all my fitness specially at my age love reading article all the best Eric

    • Hi Eric, thanks for reaching out. Glad you enjoyed that article, you need to take a listen to our podcasts, we have many more inspiring guests, some with tales of runners who started running in their 80s and even 90s! Here is the link to the one with Margaret Webb: let us know what you think, and keep on going with yours!

  10. Thanks for the article. It explains why I am struggling so much in this 10K clinic. I came off a heavy ski season which included a 7 day late spring back country trip where we climbed 8000 to 12000 feet a day. I then flipped myself into a 1/2 marathon clinic that was 3 weeks already started and ended up with a back injury which took 4 weeks to heal. Then I had a big surgery which recommended at least 6 weeks off. At week 4 I tried a 5K run on my own which took 33 mins and it exhausted me for a week and caused quite a bit pain. The 10 K clinic started that week and I didn’t go but I did an 18K hike that weekend, again, jelly legs for a week. Finally went to clinic and can’t believe it. I am huffing and puffing like crazy. Tonight was a tempo run, 6K, 2K warm up, 3K race pace, 1K cool back. I could not hold the tempo pace for more than 1.5K, god almighty it sucks!

    I am so darn slow its ridiculous. The 10K LSD this Sunday will be the start of week 5.

    I chose the 10K clinic as I knew after 10 weeks off I had to start small but holy hannah, I never thought it would be this hard! I always run a 1/2 marathon in the fall, this will be the first time in 8 years I haven’t.

    To get my running fitness back faster should I push to add more easy running days. I run 3 days per week now because I love to mountain bike on a Saturday, I live near Banff Alberta. I am still recovering from the hernia repair and my muscular strength is pathetic. I can’t believe I have deteriorated this much. If that represents 40%, I am never going to be ready for ski season in time. What to do…..sigh

    • Hi Erica, thanks for reaching out. Try not to lose hope, your body will remember what it is doing before you know it, and you will get that running fitness back. It would be best for you to make sure you incorporate easy runs as that is the biggest mistake most runners make (and what puts most runners at risk of injury). The cross training you do will help you more than you realize, so keep that up. You may also enjoy this podcast episode about cross training This will show you that you may actually end up in good shape once that fitness translates over to running. Be careful you are not putting yourself at risk of overtraining by trying to do too much too soon though! Let us know if we can help with anything else 🙂

  11. I took exactly a month off running due to a chest cold, and while my endurance fell (for the first run, anyway), I’ve been consistently faster than since before I took my break (I used to average about 6:20~6:50 per km, and am now averaging between 5:52~6:10 per km). I even did my first 10km run at 6:11 per km about twelve days after I got back into it, and I have no idea how I bounced back so fast. Not that I’m complaining, I’m just curious.
    I’m relatively new to running (started in April this year), but I don’t know if that has any bearing on anything.

  12. Hi, I’m in high school and I’ve been an avid runner since freshman year. I run cross country. We start training in May and end in late October, early November. I took the November and December off because I seemed to have lost my love of running briefly. I got a little burnt out on the 5am practices. Our old coach left and I didnt like my new coach. She had us doing too much speed work and not enough mileage. I gained too much muscle during the season (I usually get slimmer, leaner muscles during cross country and gain muscle during track) and now I’ve lost quite a bit of endurance. I went on a 5 mile run today. I stopped a few times and I never stop. What should I do to get my aerobic base back?
    Thank you for your time,

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