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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