How Long Does It Take to Lose Your Fitness?

It may be a vacation or the hectic work schedule. Or maybe you get injured or just struggle with your training motivation. There are various interruptions that can take you away from your training routine or even force you to take a longer break.

Whatever the reason is, you might worry how time off affects you and how rapidly your fitness declines.

Unfortunately, it declines quite quickly – especially when it comes to cardiorespiratory fitness and VO2 max, which is what we will be discussing in this blog. Many training adaptations take months or years to develop but are undone in weeks. Firstbeat VO2 max fitness level on select Garmin smartwatches defines your fitness level and helps you monitor if it is going up or down.

Firstbeat VO2 max fitness level (maximum oxygen uptake) defines your cardiorespiratory fitness and helps you monitor if it is going up or down if you have fallen off the workout wagon.

Rest is essential – to a moderate extent

Before we go deeper into detraining – that is the term for loss of training-induced adaptations in response to an extended break or insufficient training load – it is good to emphasize that fitness loss is a complex and unique process. Detraining depends on several factors including your fitness level, how long you have been exercising, and your personal physiology and genetics.

Another thing to keep in mind is that detraining is not the same as recovery, which is an essential part of any training program. Recovery gives your body a chance to adapt to the training and makes development possible. Firstbeat recovery time advisor helps you by predicting how long it takes before your body is fully recovered. All-day stress and recovery gives you a bigger picture and reveals how your body reacts to the challenges of daily life.

A short workout break is also the secret behind peaking. If you have been training hard and your training status is productive, a few days off is probably just what you need to get the most out of your performance. 

But enough is enough. After a few days of inactivity, detraining begins to occur, and your fitness starts to gradually decline. Cardiorespiratory fitness is like many skills: You need to use it, or you lose it.

Blood volume decreases, heart rate increases

What happens if you stop endurance training? One of the first impacts is the decrease of your blood volume – you start to lose the training adaptation that keeps your stroke volume (the amount of blood pumped by the heart with each beat) high. This means that less blood returns to your heart with each beat, which your body tries to compensate for by increasing heart rate.

This is why you might notice that your heart rate is a lot higher when you exercise at the same intensity after a training break – even a fairly short one. Usually it doesn’t take a week before blood volume begins to drop.

Also, the reduced dimension of the heart muscle and diminished ventilatory efficiency already decrease stroke volume after a few weeks of detraining. Eventually, this can’t be counterbalanced by heart rate, and your aerobic endurance is impaired.

VO2 max drops fast

The decline in stroke volume is also one of the main reasons why your VO2 max begins to decrease fairly quickly. Significant reductions in VO2 max occur within 2 to 4 weeks of detraining: Highly trained individuals might lose anywhere from 4 to 14 percent in this time, while beginners’ VO2 max declines to a lesser extent.

In addition to the decline of stroke volume, VO2 max is affected by many other factors if detraining continues. Decreases in capillary density (the tiny blood vessels that carry oxygen to your muscles), amount of mitochondria (aerobic powerhouses of your cells) and oxidative enzyme activity all affect your muscles’ ability to utilize oxygen.

During long-term training cessation, highly trained individuals have been shown to decrease their VO2 max by 6 to 20 percent. When it comes to recently trained, most studies indicate a complete reversal of VO2 max after long-term inactivity. Because VO2 max is not only the defining metric of cardiorespiratory fitness but also a great indicator of overall health, this is not a trifling matter.

Detraining also induces other adaptions, including metabolic and hormonal changes. For example, your muscle glycogen levels (the carbohydrate storage) decrease and your lactate threshold lowers in as little as one week.

If the training break continues, you begin to lose your muscle mass as well, usually after 2 to 3 weeks. Strength can be maintained a bit longer, up to 3 to 4 weeks, but thereafter it is also gradually lost. Naturally, all detraining adaptations depend on how inactive you are.

Training intensity is the most important factor when it comes to maintaining aerobic fitness if you want to maintain your VO2 max fitness level.

Intensity is important

During your training break, voluntary or forced, it is good to remember that all physical activities help in maintaining your fitness and fighting against detraining. So take the stairs and walk to the corner store at least, if that is possible.

It is good to be aware that training intensity is the most important factor when it comes to maintaining aerobic fitness. You can lower your training volume to a surprisingly great extent – even by 60 to 90 % – and training frequency can also be moderately reduced, but the intensity should be almost the same if you want to maintain your VO2 max fitness level.

If you need to cut down your training routine during your busy working days or summer holiday, train less – but train hard enough.

That said, don’t worry too much about relatively short breaks. If you have been training regularly and efficiently, you can easily hang up your running shoes for a week or two. The fitness loss that occurs during that time comes back quickly when you start training again.


Mujika, I. & Padilla, S. (2000a). Detraining: loss of a training-induced physiological and performance adaptations . Part I. Sports Medicine, 30. 79-87.
Mujika, I. & Padilla, S (2000b). Detraining: loss of training-induced physiological and performance adaptations. Part II. Sports Medicine, 30. 145-154.
Bosquet, L. & Mujika, I. (2012). Detraining. In I. Mujika (Ed), Enduranve training  – science and practice (pp. 99-106). Vitoria-Gasteiz, Basque Country: Iñigo Mujika S.L.U.