Want To Regain Fitness? How Long It Takes To Lose + Regain Your Fitness

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Although it can be mentally and physically hard to initially start running or working out, once you establish a consistent fitness routine, getting yourself to take breaks can be hard.

However, rest days are an important part of any training program and provide the recovery time your body needs to actually adapt and build back stronger to reap the benefits of your workouts.

But what happens when you have to take a longer break? Whether an injury, illness, life transition, or lack of motivation has you taking an extended time off from working out, you might wonder how long it takes to lose and regain fitness.

In this guide, we will try to answer the common questions about detraining, such as “How long does it take to lose and regain fitness?” and “How long does it take to regain fitness after time off?

We will look at: 

  • How Long Does It Take to Lose Fitness?
  • Factors That Affect How Long It Takes to Lose Fitness
  • How Long Does It Take to Lose and Regain Fitness? Cardio
  • How Long Does It Take to Lose and Regain Fitness? Strength
  • The Takeaway: Losing and Regaining Fitness

Let’s get started!

Two people holding hands in a plank position at a gym.

How Long Does It Take to Lose Fitness?

So, you are forced into a break from your workout routine. Perhaps it’s an injury, maybe you have been sick, took a fun vacation, or were in the process of moving or switching jobs and simply didn’t have the time. 

Regardless of the cause, how long does it take to lose your fitness when you stop working out?

Losing your fitness, which is referred to as detraining, is inevitable should you stop consistently exercising for weeks or months on end and just assume a completely sedentary lifestyle. 

However, the good news is that in the same way it takes time to get in shape when you first start working out, it takes time to lose your fitness when you stop working out. 

What does “losing fitness” mean practically? Losing fitness is just a loose term used to describe a partial or complete reversal of your improvements in your physique and physiology by consistently exercising. 

Detraining, or a loss of fitness, can include a decrease in aerobic endurance or stamina, a decline in VO2 max, a decrease in muscle mass, a decrease in muscular strength, a decrease in muscular endurance, changes in body composition, and “definition,” a decrease in power and speed, among other performance declines.

A class of people holding on to kettle bells.

Factors That Affect How Long It Takes to Lose Your Fitness

There’s no magic number for how long it takes to lose fitness after you stop exercising, though some general guidelines exist. However, the specific answer to “how long does it take to lose fitness” will depend on several factors, including the following:

#1: Your Level of Fitness Before You Stopped Exercising

The biggest factor affecting how long it takes to start seeing a decline in fitness after ceasing your workout routine is your fitness level before you stopped exercising. 

In general, fitter athletes who have been exercising consistently for months or years will hold on to their fitness better during time off than beginners who have only recently begun working out.

The concept of “muscle memory” shows that experienced athletes will also regain fitness a little faster after time off than people who had not exercised consistently much before stopping.

#2: Your Age

As we age, athletic performance declines due to sarcopenia and hormone changes.

Accordingly, studies show that older adults tend to lose strength and fitness gains faster and more completely (returning to baseline levels) compared with younger adults after stopping an exercise routine.

A person skipping.

#3: Why You Are Taking a Break

Not all time away from exercise will necessarily have the same effects on the body. If you are busy, have lost motivation, or are otherwise just not as active, you might not lose fitness as quickly as if your body is trying to bounce back from the added stress of trauma or injury. 

Research shows these stressors can have a more significant deleterious effect on muscle protein synthesis, and as a result, strength loss during an illness or trauma may be more significant than during an elective break.

#4: Workout Intensity 

One study found that not only does higher-intensity interval training (HIIT) induce greater gains in strength, anaerobic power, and fitness, but these gains seem better preserved during prolonged periods of time off from exercise relative to fitness gains achieved by moderate- or low-intensity continuous exercise. 

#5: The Type of Fitness

We lose cardio or aerobic fitness and strength or muscular fitness at different rates, so if you’re wondering how long it takes to get out of shape, the answer will vary based on what aspect of fitness you’re referring to and the types of workouts you were doing before you stopped exercising.

A fitness class of people doing isometric squats.

How Long Does It Take to Lose and Regain Fitness? Cardio

If you stop running or doing any sort of cardio exercise, you’ll lose aerobic fitness faster than you’ll lose muscular strength.

Evidence suggests that detraining results in a rapid loss in maximal oxygen uptake (V̇O2max), blood volume, ventilatory efficiency, increased reliance on carbohydrate metabolism during exercise, lowered glycogen levels, reduced lactate threshold, decreased capillary density and oxidative enzyme activities in skeletal muscles, among changes in hormones.

One study demonstrated that aerobic fitness could drop significantly in just a matter of weeks. The study found that VO2 max dropped 7% after 3 weeks of inactivity. 

It continued to decline to 16% below the initial value achieved during training 8 weeks after training stopped. However, it stabilized, and no further appreciable losses in VO2 max were noted at the 12-week mark of inactivity.

Moreover, though VO2 max had dropped significantly (16%), it was still higher after 12 weeks of inactivity than it was in sedentary control subjects who had never trained. Therefore, though aerobic fitness drops quickly, losses in fitness slow after two months or so.

A person leaning back in a chair hands crossed behind his head.

Decreases in VO2 max during detraining were attributed to decreases in stroke volume.

Another study showed how rapidly inactivity can transform the heart. After an 18-week training program that culminated in the 2016 Boston Marathon, 21 male runners stopped all training aside from roughly 2 hours per week or less. 

Of the most notable changes, subjects saw an average decline of 6% plasma volume, 8.1% left ventricular wall thickness, 10.3% loss of left ventricular mass, and an 8.2% loss in the right atrial area after four weeks of detraining. 

While most of these changes indicate a loss of strength, mass, and functional capacity of the heart, the contribution of the first factor mentioned—the loss of plasma volume—is also significant.

The good news is that regaining aerobic fitness is absolutely possible by resuming training. Research indicates that returning to pre-break fitness is faster than the initial time course to get to that level.

However, the specifics for how long it will take to regain aerobic fitness depends on numerous factors such as your age, previous training level, length of inactivity, the reason for inactivity, and if you did any activity during your time off.

Someone doing a push up trying to regain fitness.

How Long Does It Take to Lose and Regain Fitness? Strength

Muscular strength tends to be lost more slowly than cardiovascular fitness. 

One study showed that two weeks of complete rest did not result in any loss in muscular strength.

However, there is evidence to suggest that strength starts to decline after three weeks of inactivity. 

These findings indicate that the decline in cardiovascular function following a few weeks of detraining is thought to be largely due to a reduction in blood volume, which appears to limit ventricular filling during upright exercise.

In terms of rebuilding strength, one study found that elderly men who stopped training for 12 weeks were able to regain strength relatively quickly. After the 12 weeks of detraining, they lost about 30% of their strength, and their muscle size (type I and II fiber cross-sectional areas) returned to pretraining values. 

Interestingly, after about 8 weeks of retraining, strength was back to its pre-break values. Muscle fiber morphology did not return to its trained values, which the researchers concluded was indicative that strength gains were due to neural adaptations.

Someone stretching their arm outside.

The Takeaway: Losing and Regaining Fitness

Most people find themselves needing to take prolonged time off from working out at one time or another.

You won’t lose much if any, fitness after a week or two, but after two weeks, aerobic fitness starts to decline.

For muscular strength, the outlook is better. You’ll start to lose strength after 3 weeks, so a break of 3-4 weeks shouldn’t result in significant losses.

The good news is that the fitter you are, the faster you will regain fitness once you’re back into your workout routine.

Take things slowly, listen to your body, and understand that it’s all part of the journey.

If you need some motivational hacks to keep you inspired and in the game, check out our article on how to keep that motivation up!

A close-up of a person's running shoes walking up stairs.


Photo of author
Amber Sayer is a Fitness, Nutrition, and Wellness Writer and Editor, as well as a NASM-Certified Nutrition Coach and UESCA-certified running, endurance nutrition, and triathlon coach. She holds two Masters Degrees—one in Exercise Science and one in Prosthetics and Orthotics. As a Certified Personal Trainer and running coach for 12 years, Amber enjoys staying active and helping others do so as well. In her free time, she likes running, cycling, cooking, and tackling any type of puzzle.

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