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I've heard people say that, if you're seriously trained and take a small break, you may lose strength, but the ability to get it back is beyond that of a lesser trained individual. In other words, if you take a few weeks off, you can probably get back to where you were in just one week's time max.

Is fitness this way too? If you were once very fit, is it easier to become equally as fit once again?

Because some people discuss how hard it is to get fit from step one. If you were and have been highly fit all of your life and take a set back of a few months, can you get fit again in a shorter time than when you, say, first ever became fit? I know because I've read of people who regained muscle quicker.

Basically, sort of like how muscles can adapt quicker if they've been used for long periods of time.

The question that's claimed to be similar to this one fails to address the cardiovascular aspect of training. I expected insightful answers regarding cardiovascular adaptation, not muscular adaptation.

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    @EricKaufman - Related, and very close, but I don't think a duplicate. Answers for fitness should also include the increase in biomechanical efficiency from (presumably) better form after more practice of the fitness activity. You get more activity for less effort, which is a component of being fit. – JohnP Jun 17 '17 at 0:41
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One last attempt. Hopefully this article helps.


It’s the runner’s biggest question and worst fear: how quickly can I get out of shape? After putting in hours of training and hundreds of miles, most athletes worry it will all go to waste if they stop.

That’s only partially true.

Unfortunately, plenty of hard-earned fitness can go away within two weeks. Most studies suggest that an athlete’s VO2 max, the maximum oxygen he or she can uptake and utilize, plunges in the first month of inactivity, according to Dr. Edward Coyle, the director of the Human Performance Lab at the University of Texas at Austin. VO2 max continues to decrease, albeit at a slower rate, for the first three months after ceasing activity. In highly-trained athletes, VO2 max decreases by 7 percent in the 12 to 21 days after stopping training and another 9 percent during days 21 to 84. In athletes who have trained for a few months, and increased their VO2 max with exercise, those changes are completely reversed with several months of not training.

“It’s all about supply and demand. If you stop running, you take away the demand,” said Jason Karp, a coach and author of Running a Marathon for Dummies.

All the biological systems that come into play when we run are closely connected, so while VO2 max might be one of the most noticeable and important changes, it’s not the only one. Blood volume also rapidly decreases, which affects oxygen uptake. Mitochondrial density, lactate threshold, and the ability to oxidize fat stores all decrease. Even the enzymes involved in metabolizing energy decline and become less active.

“What really changes is the ability to consume and process oxygen,” said Karp. After endurance and cardiovascular abilities take a big hit initially, muscle mass and strength also begin to atrophy. In practice, runners often notice that while endurance capabilities go first, it can be possible to hang on to some speed for longer.

Now, the good and bad news: all this depends on the individual. Ann Alyanak, who won the 2011 Columbus Marathon and was the 2002 Big Ten champion in the 10,000m, sees a wide variety of detraining effects with her athletes, particularly when she was coaching college. Some athletes would be fine after a week or two of not running and other athletes would lose fitness in that same time frame.

How quickly that happens can also depend on where an athlete is at in training. “If you’re at peak fitness, then it goes really fast,” Alyanak said, often because you’re already tapering. “You’re holding onto it anyway, at the end of the rope.”

And, if you’ve been training for a long time, then you can maintain some fitness longer. Long-term athletes are often in a better position than those who have been running or working out for a shorter period of time. That can be true even after months of inactivity.

“If you’ve done it in the past, it’ll come back faster,” said Alyanak.

Elite athletes or those who have trained consistently for upwards of 10 years may see more rapid decline initially than people who haven’t been exercising as long. The elite athletes simply have further to fall. But highly-trained athletes don’t decline to the same levels as less-trained individuals, even after three months of no activity — and, in most measures, they certainly don’t decline to the level of people who have never exercised.

“Endurance athletes, however, do not regress to the levels displayed by individuals who have never trained,” wrote Coyle in a scholarly review of the topic.

If getting back in shape after taking time off, whether for injury or a mental break, seems like it takes far longer than getting out of shape, that’s not just your perception.

“It takes at least twice as long, if not longer, to gain fitness as to lose fitness,” said Karp. “It takes much, much longer to build a house than to knock it down.”

Many of your systems have to be built back up from the cellular level, synthesizing protein and increasing the number of mitochondria. The half-line of decline in mitochondrial enzyme is 12 days, which means 12 days of detraining requires 36 days of re-training to return to the same levels, according to Coyle.

Much, if not all, of the decline in fitness can be alleviated, though, through cross-training and through shorter intense efforts. If the intensity is kept up two or three times a week, then the overall training volume can decline without extreme decreases in fitness. When athletes taper before races this is exactly what they’re doing: maintaining fitness through short, hard efforts, but allowing their bodies to rest with less overall training volume.

“You don’t need as much of a training load to maintain fitness,” said Karp. Losing fitness is not a reason, however, to not take a needed break — a fear Alyanak says pushes too many athletes not to rest. A yearly offseason is important for physical and mental health and can allow an athlete to come back stronger. Rest periods for injury or illness, particularly if they allow some cross-training, are far better than poor training and hurting yourself.

“You’re not going to get out of shape in a few days,”

Article from competitor.com

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Cardiovascular Exercise Adaptations

Aerobic exercise causes important cellular and vascular changes including:

  • Increased number of mitochondria (intracellular respiration). Simply put with more mitochondria, you can produce more energy (ATP).
  • Your heart becomes more efficient. With each beat more blood is pumped to your body resulting in a increase of available oxygen.
  • Capillary density increases. Resulting in an increased amount of oxygen and nutrient rich blood delivered to your muscles

Cardiovascular Development vs Detraining Rates

  • These changes gradually occur in approximately 4-8 weeks.

  • These beneficial adaptions disappear when you stop training. Detraining occurs approximately 2 times faster than the development rate.

  • Not exercising for two to eight months leads to loss of virtually all fitness gains. The loss of aerobic capacity occurs much more rapidly than declines in muscle strength.


  1. http://jap.physiology.org/content/60/1/95.short
  2. http://circ.ahajournals.org/content/122/12/1221.short

Weight Training Adaptations

  • When you start weight training, during the first 3-4 weeks strength gains are due to nervous system changes.

  • You’re getting stronger due to an increase in muscle fiber activation (you’re training your brain to activate previously dormant motor neurons).

  • In addition, you’re also training your nervous system to decrease activation of the opposing muscle group. Essentially you’re getting stronger without any change in muscle size.

  • After 3-4 weeks strength changes are due to increase in muscle fiber diameter (called hypertrophy). A common misconception is that the number of muscle fibers is increasing (this is called hyperplasia).

Muscle Development vs Detraining Rates

  • Detraining occurs differently with strength training. Neural changes remain, so a formerly conditioned person can regaining lost muscle mass faster compared to someone that has never weight trained.
  • Muscle mass also takes approximately 2 times longer to lose than it takes to initially gain.

  1. https://www.researchgate.net/publication/50401359_An_examination_of_the_time_course_of_training-induced_skeletal_muscle_hypertrophy
  2. http://sci-fit.net/2017/detraining-retraining/
  3. https://www.ncbi.nlm.nih.gov/pubmed/16464122
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  • This not answering my question specifically, but thanks for your efforts. – user25900 Jun 17 '17 at 0:32

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