How fast do you lose fitness when you take a break from running? –

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Whether it’s due to injury, a holiday or a voluntary break, here’s what happens to your body when you take a timeout from training

There’s a common saying that fitness is hard won and easily lost. Bodies respond and adapt to stimulus (training) – to get fit, we train and, when mixed with good recovery, we build fitness. But what happens when you remove the stimulus – when you pick up an injury, go on holiday, take a planned break or simply lose your mojo?
It’s true to say that you get fitter when you recover from your training, not as you carry it out. Remember, rest days or short periods of recovery are necessary to help recharge your mind and body to work harder. But what happens physiologically when we stop training for longer than a regular rest or easy day? Different people will ‘atrophy’ or detrain at different rates according to their genetics, lifestyle and nutrition, so treat this timeline as a broad indication, not set in stone:
3-5 days: This is a period when many runners already start to feel they have lost a lot of fitness and start to worry and lose confidence. In reality, though, there is little to no loss of fitness from any of the key cardiovascular measures over this timescale. VO2 max and cardiac output broadly remain the same. In fact, for many runners a handful of days off will leave them fitter and stronger as your body absorbs the harder training in the days prior to the break. So in short if you need to stop to get over a cold, you’re worried about a small niggle or life has just got in the way, don’t panic. (Though if you’re taking periods like this off regularly, it’s likely that a lack of consistent training stimulus will be slowing your progress.)
5 days-3 weeks: Some changes occur beyond about five days which, over time, start to impact fitness. Your blood plasma volume starts to decrease, which leads to a decrease in cardiac output – in short, less oxygenated blood to your muscles. After about 10 days we start to see a knock-on reduction in VO2 max, between 4-5% after two weeks. After a period of a few days your body can start to become less efficient at firing muscle fibres, which might explain some of the ‘rusty’ feeling you get after a few days off.
No exercise throughout a period of weeks means your heart will not be working as hard, and you will start to see reductions in your cardiac muscle size, and so your stroke volume (the amount of blood pumped from the left ventricle of the heart per beat) decreases. In addition, your body becomes less efficient in the way it uses glycogen.
While these changes sound dramatic, many can be reversed quickly when you return to training. Runners shouldn’t be fearful, therefore, of taking a longer period of time off to recover from a key race, go on holiday or to give an injury or niggle a real chance to heal properly.

1-2 months: In addition to a continuation of the changes mentioned above, our body is becoming less efficient at burning stored fats as an energy source, our ability to sustain high-intensity efforts starts to reduce significantly and the body loses both capillary density and some of its ability to use oxygen to create energy in the muscles; as our mitochondria become less efficient, we’ll find it harder to control the production of lactate as we train.
Of course, we will also have lost a deal of confidence by this point, with a loss of mental callousing to sustained efforts. Returning to training after one to two months out can again see fitness return quickly but should be treated with more caution. We will have lost some of our muscular strength and conditioning, although this takes a little longer to atrophy than our cardiovascular fitness. As such we will need to build back cautiously to prevent injury.
3-6 months: Our body has now started to return to a relative baseline of fitness. Depending on your level of training and experience this baseline might still be quite high compared to others. There is evidence to suggest individuals with several years of training behind them are able to maintain more of their fitness after periods out. With time and patience all runners can build training back to where they were pre-injury but this will likely take a period of weeks or months.
The first thing to recognise is there is no need to panic. In fact, a few days off or even a planned block of time off running after a big training block might be a great thing to include to allow your body and mind to recover properly and recharge your motivation. You can mitigate or manage many of the detraining effects mentioned above with these strategies:
Active recovery: If you are having a period off running after a key race or during a holiday there is nothing to stop you remaining physically active and mentally healthy. Walking, cycling or swimming are great ways to maintain physical activity during a period of two to three weeks off running.
Cross-training: The early effects of detraining such as reduced blood plasma volume and cardiac muscle will be mitigated or indeed completely prevented by including cross-training, provided it can be done without making an injury worse. For runners who aren’t injured, cross-training can provide a mental break from running while still maintaining fitness.
Minimum load: There is no standard minimum level of cross-training required in order to maintain fitness. Ultimately this will depend on the volume, intensity and frequency of the running you were doing. For most runners, though, three or four cross-training sessions a week replicating the volume and intensity of your previous running training could work well.
Maintain a pattern: One of the hardest aspects of an extended break from running is losing a pattern and rhythm of training. Life shifts, routines change and finding time and space but build running back in can prove challenging. Trying to maintain a pattern by replacing your runs with your rehab, Pilates, yoga or cross-training can make it easier to pick back up when your body is ready to run again.
Some runners aren’t forced to take a break due to injury or race recovery but purely because life gets in the way, and time is short. However, a lot can be achieved in 30 minutes of running or cross-training so try not to let a desire to do the ideal training prevent you from doing some training. Here are just a few sessions which can be completed in 30-40 minutes and which pack a physical punch:
10/10/10 progression
Build intensity each 10-minute block to run or cross-train the final 10 minutes at 7-8 out of 10 effort level, the effort you feel you could sustain for an hour-long race, or 85-90% of your maximum heart rate (MHR).
Split threshold
Do 3-4 repeats of 5 minutes at 7-8/10 perceived effort, one-hour race effort or 85-90% of your MHR with 60-90 secs recovery.
12 x 60-secs with decreasing recovery
Warm up well and run 12 sets of 60 secs at around 5K race effort with rolling recovery periods (60s, 45s, 30s, 60s, 45s, 30s etc)
5/4/3/2/1 Fartlek
Warm up and run or cross-train efforts of 5 minutes at one-hour race effort, then increase effort as the reps get shorter – 4 mins, 3 mins, 2 mins, building down to 1 min at 3-5K race effort. Take 60-75s recovery between each.
Tom Craggs is a coach and Road Running Manager for England Athletics


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