The Science Behind Detraining

Written By Chris Taylor

Chris is Operations Manager at Ultra X and takes the lead on planning new races and events. His interests include (and are limited to): ultra running, plant-based foods to eat whilst ultra running, and ultra running with dogs.

22 April 2020


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Reading Time: 8 minutes

Sporting events the world over have ground to a halt. Six Nations fixtures were the first to fall, then mass participation marathons and indoor competitions, swiftly followed by international athletics, domestic team games, anything with ‘world tour’ in the title and, eventually, begrudgingly, apologetically, the Olympics. And now, with popular running parks and local athletics tracks also closing their gates, even the everyday athlete has been left wondering where their next endorphin fix is going to come from.

If you’re a runner, it’s likely you spent the winter months doggedly building up your aerobic base, logging weekend long runs on wet and cold Saturday mornings, with the aim of being in the best shape of your life come springtime when the big city marathon you’ve been losing sleep over for the last two months finally rolls around, and you can prove to your friends and family once and for all that all those hours you spent plodding around alone in the rain were TOTALLY WORTH IT.

And now, after all those early nights, all those beers abstained in favour of protein shakes, your big race has been cancelled. You now spend more time on Zoom than you do asleep, training sessions (once a welcome obligation) are now a total luxury and surely, SURELY, it’s only a matter of weeks before you lose all your fitness and resort to Googling “couch to 5k”. Sound like a familiar thought process?

Fear over losing fitness can compel athletes to make some very poor judgement calls. Runners in particular seem curiously prone to behaving like Joe Exotic in a legal battle: refusing to be stopped by anything, let alone such trivial matters as global pandemics and worldwide lockdowns, compelled solely by the justification that they’ve worked hard for their fitness and aren’t simply going to throw it all away watching Netflix. Somewhat ironically, this can often lead to the opposite of detraining: overtraining, soldiering on through sickness or injury, all in the name of not losing those cherished winter gains.

But is that fear justified? Despite how rapid fitness loss may seem and how lethargic you may feel having reduced your workload, it turns out it’s quite difficult to lose more than a few percent of your gains, and it will certainly take more than a few lazy Sundays and the entire back catalogue of Louis Theroux documentaries to take you back to square one.

Detraining: what is it?

Detraining (or ‘reversibility of fitness’, as it’s sometimes known) describes the reduction in fitness that occurs through a decrease in training volume or a complete halt to training. To understand how it works, it’s necessary to first understand the timeline of training (fitness improvement), since detraining (fitness decline) is very nearly the inverse.

If you can remember, cast your mind back to when you first started running. It’s highly likely that the following series of events unfolded:

  • It was really hard at first. You plodded around awkwardly like Bambi on ice, everything hurt and you felt stiff and tired after each session. This probably lasted a few weeks.
  • After some good months of persistent training, the awkward sensation disappeared completely. You improved quickly, nabbed a few local Strava segments, and gradually became addicted to the feeling of consistent improvement. You were invincible.
  • A year or two down the line, you hit your first rut. The tiniest improvements took weeks of hard work to develop, your last PB was the net downhill 5k you raced at Christmas for a laugh, and you blame external circumstances entirely (age, work commitments, shoes, and weather are common variables).

This probably sounds familiar because training (fitness improvement) follows a curvilinear path. Picture the elevation chart of a flat-topped mountain – it goes up quite steeply at first and then plateaus. This pattern of growth is universal because we can only sustain training progression at a certain rate.

Despite what the loudmouth at the office who spent five grand on a TT bike and once did an Ironman will tell you, nobody can go from not running at all to running 100 miles a week in a short period of time. Sophisticated workouts matter much less than you might think at the beginning – you improved quickly because you started with nothing. When you eventually become an optimised running machine, improvements are harder to identify and achieve, requiring a fine tuned training program and the guidance of a coach to accomplish.

How does detraining work?

Detraining then, works in reverse. Regardless of whether you go from 100 miles a week to 50, or 50 miles a week to sedentary, the detraining effect will be more marked initially and will become more subtle later on. Key physiological measurements (VO2max, cardiac output, pace at lactate threshold etc) and overall performance will decline steadily at first and then level off.

However, unlike the universal experience of fitness improvement, reversibility of fitness is quite specific. The speed at which detraining occurs and the overall effect that it has will depend on several factors, such as your experience, the type and quantity of training undertaken before you applied the brakes, and your training response following your emergency landing.

The effect of training reduction in numbers

Unsurprisingly, the more experienced athletes are more resistant to detraining. The deep and chronic training adaptations that accumulate over a long period of time take a long time to reverse, even if the seasoned athlete stops entirely. However, while complete training cessation can certainly mean big losses for the everyday athlete, the news for those reducing volume but not coming to a total standstill is better than you might think.

Notably, a little effort goes a long, long way. Even a 50% reduction in training volume (maintaining as few as three sessions per week) will only equate to approximately a 5-10% reduction in fitness. You will also return to prior fitness levels and Strava obsession in just a few weeks.

That said, if, when lockdown began, you hid your trainers at the bottom of the wardrobe and began focusing all your energy on watching every episode of Lost before lockdown ends, then you can expect a performance decline of more than 20% within several weeks. Ouch.

To break it down, here are some example training reduction scenarios with estimated detraining effects (note: all numbers are theoretical estimates based on the relevant research in this area):


  • Training reduction of 10% > little detraining effect, return to prior fitness in a week
  • Training reduction of 50% > 5-10% detraining effect, return to prior fitness in a few weeks
  • Training reduction of 70% > 15-20% detraining effect, return to prior fitness in several weeks
  • Training reduction total (your running shoes assume you’ve died) > significant detraining effect, return to prior fitness in several months

How to manage detraining effectively

Wherever you are in the world, it’s safe to assume that your training is going to have to adapt to the current chaos and your fitness is going to be impacted. Enter that most fabled of all ultra marathon proverbs: control the controllables. Whilst you cannot change your overall experience level or the training you logged prior to Coronavirus, you do have control (most of the time) over the last determining factor of detraining effect: your training response now.

So, what should you do? Here are some things to bear in mind:

  • Doing little is a lot better than doing nothing: Though any fitness losses during the first week of inactivity are minimal (you may even experience small fitness gains in the first few days as you recover fully from prior training), going full couch potato for a few weeks will result in a significant fitness degradation (>20%) for even the fittest of athletes. However, conducting a relatively small amount of training (30-50% of your previous volume) can result in fitness losses of single digit percentages.


  • Many aspects of fitness are transferable: Perhaps you’re in a country where you can’t exercise outside right now, but maybe you have an indoor cycling machine gathering dust in the garage. Though some sports require specific conditioning (you’re unlikely to find hill sprints easy when the shackles come off), many aspects of fitness (expanded blood volume, aerobic capacity, efficient utilisation and storage of glucose etc) are transferable between sports. Remember that turbo you bought after reading an article on cross training but never used? Get it out and start pedalling. A good proportion of the benefits will transfer to the trails when you lace up your trainers again.


  • Consider HIIT workouts to keep that ‘top end’ fitness: Don’t have an indoor cycling machine? Not even sure what a ‘turbo’ is? Don’t worry. Virtual workouts are ten a penny right; scroll through your Instagram feed for five minutes and you’ll likely come across a few advertisements for live High Intensity Interval Training (HIIT) workouts. They usually require little to no equipment and if you can find a PT whose enthusiasm doesn’t make your head spin, then doing even short bouts of activity (multiple repetitions of 30 seconds max effort) can have an impressive impact on fitness and help flatten out that detraining curve.



  • Maintaining fitness is a worthwhile goal: In the current age of constant progression, it’s easy to fall into the trap of thinking that if you aren’t moving forward, you may as well be moving backwards. Well, where fitness is concerned that’s simply not true. Departing this period of uncertainty equally as fit as when you entered it would be a significant achievement. What’s more, fitness maintenance can be accomplished with very little training stimulus, affording you more time to repaint the kitchen or read the complete Winnie the Pooh collection, whatever it is that you’ve had on your to-do list for years.


  • Reducing training volume and intensity can have advantages: Although being in the thick of a goal-focused training program can be an addictive process, it doesn’t come without risk. A high volume, high intensity training schedule can weaken your immune system (not what you want right now) and make you more susceptible to injury (not what you want right now x 100). Be grateful for the opportunity to slow down the pace for a few weeks, develop an indestructible aerobic foundation, and build some long term tissue resilience in your muscles and tendons.

For more general guidance on how to make an opportunity out of lockdown life, check out our ultra running isolation tips.

The message

The message here is simple: don’t be afraid of losing fitness. If your current circumstances mean you cannot train or you simply decide to back off for a few weeks, don’t worry. In the hypothetical training reduction scenarios above, all but the sedentary athlete would be able to return to prior levels of fitness within a few weeks. Significant detraining effects are almost as hard to achieve as significant training effects and are certainly not the sort of foregone conclusion ‘this-will-take-months-to-bounce-back-from’ nightmare that the typical runner imagines.

If you’re quarantining in a first floor flat with your in-laws, struggling for time, lacking motivation, or your movements are limited due to government restrictions, it’ll be okay. Avoid doing absolutely nothing, incorporate short, high intensity workouts if you can, and enjoy the downtime. Most importantly of all, do not overtrain in response to the fear of losing fitness. It’s a zero sum game at best, and an injury waiting to happen at worst. Focus on the stuff that will make you a better you (pro tip: this doesn’t always mean running) and you will come out the other side a better athlete.

(Incidentally, if you are struggling for motivation, there’s an easy fix for that).


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