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Falling off track from your workout routine is inevitable. Life happens. You go on a trip. You sprain your ankle or start a new job. Then, once you find the time to resume training, you feel weak and out of breath. It can seem like all your good work has been for nothing. But that isn’t the case.
Although we do lose fitness shockingly fast, it turns out that we don’t simply go back to square one. What’s more, even when circumstances keep you from your regular routine, there are various things you can do to minimise the losses.

This article is part of a series on fitness that answers eight questions about exercise and its influence on our bodies and minds. Read more here.

How rapidly fitness declines depends on what aspect of it you consider. The news is worst when it comes to aerobic fitness. Evidence suggests that VO2 max, the maximum rate at which the body can absorb oxygen, drops significantly after a mere 12 days of inactivity, largely due to a roughly 10 per cent decrease in the amount of blood your heart can pump with each beat.
Some changes occur even sooner. For instance, blood volume decreases after two days of rest. After a month, we have fewer capillaries delivering oxygen to our muscles too, possibly due to changes in levels of a protein that affects capillary formation.
Out of breath
In a preprint paper from June, Adam Sharples at the Norwegian School of Sports Sciences and his colleagues found that improvements in VO2 max from two months of training evaporated after…