How Long Does It Take To Lose Fitness?

We have all been there at one point or another: the fear that begins to creep in when we have to take a day off from training. Whether this is due to energy levels, family/life obligations, or injury prevention, a day can feel like an eternity for most endurance athletes. What would happen if that day became 7, or 21 days off?! While the thought of taking three weeks off from training sounds disastrous, depending on the time of your season, it could be just what the body needs. 

Rest is not something to be feared, but needs to be understood of how it plays a pivotal role in your training cycle: you can only train as hard as you recover. So then where does this fear of recovery come into play? At what point do we actually begin to lose fitness and can we gain that fitness back? 

The Good News

When generally speaking, almost all training benefits are reversible to some degree. This means that whatever level of fitness you have built up over time, it is possible to lose most of this. So where is this good news? Well, in order to lose all of your gained fitness it would take multiple months, if not years, of detraining to completely erase it. 

When it comes to neuromuscular adaptations, coordination patterns are maintained fairly well during de-training, and therefore there is minimal loss from that perspective. The saying “it’s like riding a bike” in that even without riding a bike for many years you can pick it back up very quickly from a neuromuscular coordination perspective is true. You just won’t be able to pedal as hard as you previously could for very long due to the losses in fitness.

Still not convinced that a day or two off won’t completely ruin your season? Ten days to two weeks is the length of time that would be the maximum amount of days off someone could take without experiencing a (moderate) amount of detraining in regards to cardiovascular fitness.

“I very often have athletes take completely off 3-7 days in the middle of the season (sometimes a few times throughout a season) with absolutely no loss in fitness/endurance capacity.” 

Neal Henderson, Head of Wahoo Sports Science

Keep in mind when it comes to de-training, all individuals will be different. Two main factors are at play when athletes undergo de-training: the length of the de-training period and the initial training status of the individual. 

Now that we cleared that up, let’s move on to the specifics of what occurs during a period of detraining. 

Cardiovascular Changes 

In the first ten days to two weeks of inactivity/de-training, there is a measurable loss in cardiovascular fitness, but even this level of decrease is only about 2-3% drop in values such as VO2 Max, MAP (maximum aerobic power), or FTP (functional threshold power). This time period may start to trend towards some slight reductions in enzymatic activity in the muscles for high-intensity efforts (like your anaerobic capacity) within 3-4 days without any training…but those changes would be regained in just one or two high-intensity training sessions! Our bodies will immediately begin to lose mitochondrial adaptations made within the first week of inactivity. Muscle mitochondrial oxidative capacity undergoes rapid changes in both trained and untrained states. Muscle mitochondria increase within the first five weeks, almost doubling, at the onset of exercise.  On the other hand, following just one week of de-training, muscle mitochondria losses are at 50% of what was gained in the first five weeks.

Once you get more than 3-4 weeks of de-training you will begin to see continued reductions in fitness that include:

  • Decreased blood volume
  • Reduced plasma volume
  • Slight decrease in cardiac output (cardiac output = heart rate x stroke volume)
  • Decreases in oxidative enzymes in the mitochondria and muscle
  • Decreased mitochondrial density in the muscle

Over the course of the following 1 to 3 months of de-training, you might see decreases in VO2 Max in the range of 10-25%. This loss in VO2 Max Performance capabilities is largely due in part to the blood volume lost during de-training initially. As time goes on (detraining time that is) the increased deficit in VO2 is attributed to a decrease in our arteriovenous oxygen difference. The arteriovenous oxygen difference, or a-VO2 diff, is the difference in the oxygen content of the blood between the arterial blood and the venous blood. It is an indication of how much oxygen is removed from the blood in capillaries as the blood circulates in the body. 

Muscular Strength Changes

The rate of de-training effects from resistance exercise happens more slowly than what we see with endurance training. Muscular atrophy and decreases in strength are largely due to changes in the nervous system. While muscular adaptations decay much more slowly, you may conversely see an increase in peak power and muscular strength 7-10 days after detraining. 

There will be some small reductions in muscle strength and peak power reduction occurring after closer to 3 to 4-weeks of detraining, and will tend to decay at a slightly slower rate than one loses aerobic/cardiovascular adaptations.

With respect to muscle fibers, oxidative fibers in endurance-trained athletes will decrease within 8 weeks of inactivity. Fast-twitch fibers are specifically targeted within the first few weeks of inactivity, while longer periods of rest will bring about declines in the cross-sectional area of both fast and slow-twitch fibers.

Coming Back from Injury

While it may be hard to hold yourself back when you’ve been released from the doctor to train, it is important to start with appropriate cross-training and strength/foundational work to begin before piling on training volume and intensity. Each and every injury requires a unique and individualized approach, so it is important to work with your medical providers and follow their guidance. Generally speaking, though, it’s better to take a more gradual approach to rebuild fitness after injury than if returning to training after an off-season break or returning to training after an extended period without any training.

What About Off-Season??

Off-season breaks are important not just from a physical perspective, but especially from a psychological perspective. You have been physically and metaphorically “on” for months. Your life and habits are framed around training and racing, and this will require you to take some time to unwind and decompress in order to enter a new season energized and motivated. 

While a 2-4 week off-season break can lead to decreases in fitness around 10%, it is always easier to regain a level of fitness that you’ve already previously attained than it is to build to a new level. Neal Henderson of Wahoo Sports Science recounts his own experience with coaching athletes through the off-season, “I tend to see that athletes regain fitness at about twice to three times the rate that they lose it (example – an athlete taking 4 weeks completely off might need 8 to 12-weeks to fully rebuild to the same level of fitness…and then new gains in fitness will tend to come at slower rates, following the old idea of diminishing returns…it takes more work to make smaller levels of improvement).” These time frames are for already well-training individuals, though. Novices can see weekly improvements in fitness of 1-3% per week in the first 6-12 weeks of training…while experienced/already well-trained individuals might only be improving by a quarter to a half-percent per week of training.

Don’t let the doubt and fear of losing fitness interfere with your well-deserved time off. Use this time to recover physically and mentally. Time away will allow you to hit the ground running when training begins to resume! 

Mac Cassin is the Chief Cycling Physiologist at Wahoo Sports Science. He holds a degree in Integrative Physiology from the University of Colorado-Boulder and has won multiple National Championships. The experience of juggling athletic goals with collegiate and career responsibilities has taught Mac that peak performance is achievable even for those who cannot focus exclusively on training. While concentrating on exercise physiology in an academic setting, Mac competed at the World Championships, Pan American Championships and World Cups on both the road and track.

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