How Quickly Do You Lose Fitness When Not Running?

Running Training

How Quickly Do You Lose Fitness When Not Running?

An enforced rest from training, whether due to injury, illness or life is something that fills many runners with dread. There’s the irrational fear that you will lose much of your hard earned fitness overnight and will be forced to return to square one. However, just how quickly do you lose fitness when not running? The good news is not quite as quickly as you may think…

An enforced rest from training, whether due to injury, illness or life is something that fills many runners with dread. There’s the irrational fear that you will lose much of your hard earned fitness overnight and will be forced to return to square one. However, just how quickly do you lose fitness when not running? The good news is not quite as quickly as you may think…


One of the fundamental principles of training is reversibility. This means that if you stop training, the long term physiological benefits such as cardiac hypertrophy (an increase in size and strength of the heart muscle), increased blood volume and increased aerobic enzymes will start to decline. In fact your muscles will start to atrophy (decrease in size and strength) after just three days of inactivity and your neuromuscular co-ordination will often rapidly decline, which is why you may possibly feel like Bambi initially when returning to running

What does the research say?

A study by Coyle et al (1984) looked at the effects of de-training in experienced athletes over a twelve week period. The study revealed that the subjects’ initial decline in fitness was fairly rapid, and after just 12 days, levels of aerobic enzymes had decreased by 50 per cent and VO2 max decreased by 7 per cent.

However over the following weeks, further reductions in fitness stabilised and at the end of the twelve week period the average reduction in the subjects’ VO2 max was only 16 per cent below the initial trained value.

Other factors to consider

Of course, it’s important to remember that how much fitness you lose depends on a number of factors such as your training history, whether you cross train, the length of time you take off and to a certain extent, genetic and lifestyle factors too.

If you’re an experienced runner with several years of consistent training in the bank, the longer it will take you to lose fitness. It’s easy to forget that some of the long term adaptations of endurance training such as increased capillary density don’t vanish in an instant!

Your cardiovascular system doesn’t know the difference between running and other forms of aerobic activity, so if you are unable to run but are able to cross train, as long as you can elevate your heart rate, you will maintain or even improve your aerobic fitness.

Rest is not always a bad thing

Although it may seem counterintuitive, many runners are actually pleasantly surprised with their form following a break from running. When training hard it’s all too easy to forget that gains in fitness actually happen when you rest, not while you’re training.

Your body needs to recover in order to absorb the work that you have done and to allow the physiological adaptations to a training stimulus to take place. Therefore many runners find that an enforced rest can actually be a blessing in disguise, enabling your body to reap the benefits of training and your mind to recharge too. Roger Bannister took five days off prior to running the first ever sub-four-minute mile and it certainly did him no harm!