Consistent cycling forges muscles akin to granite, a visible vascular network that impresses all and a positive outlook on life.
But what happens when that consistency is interrupted by injury, illness or time-sucking life events, such as moving house or having children?
How quickly do your trunk-like thighs come to resemble twigs and your form-fitting Rapha shorts become a crime scene? Let’s talk detraining and retraining…
- Read more: The question every cyclist fears after a break from riding – how quickly do you lose fitness?
The expert's view
One man who knows more than most about this is Dr Paul Laursen. The Canadian completed his first Ironman at the tender age of 19.
Over 30 years later, he’s authored more than 200 peer-reviewed articles about exercise physiology, was physiology manager for New Zealand’s Olympic athletes (2009 to 2017) and is the brains behind AI-powered endurance training platform Athletica.
Laursen says the detraining process depends on many factors, but that fitness level before stopping cycling is arguably the biggest one.
The fitter you are, the faster it slips away. In fact, for pro riders, detraining can kick in after only three days off the bike.
That’s because their bodies are hardwired to relentless volume and constant hits of intensity. For the rest of us – say, if you’re training twice a week – even after five to six days of inactivity, there’s virtually no loss of fitness. But then the losses come.
“The first thing affected is your plasma volume – the water component of your bloodstream,” says Laursen. Plasma, among various functions, carries nutrients to your working cells.
When you detrain, its volume drops because the body no longer needs the same cardiovascular and thermoregulatory capacity it did during training.
This leads to a drop in stroke volume – the amount of blood pumped out of the heart with each beat. This means your heart has to beat faster to reach the same cardiac output (the total volume of blood pumped out each minute – heart rate multiplied by stroke volume), to deliver oxygen and nutrients to your muscles.
And if your heart’s working harder than before to produce the same wattage, you’ll hit your physiological ceiling sooner.
Research in 1986, in the Journal of Applied Physiology, revealed that a period of detraining of between two and four weeks for athletes whose VO2 max was 50-60ml/min/kg saw a 9-12% drop in stroke volume, stimulated by a 12% drop in plasma volume.
There’s a metabolic impact, too. “After two to three weeks, mitochondrial enzymes begin to disappear,” says Laursen. Mitochondria are the body’s powerhouses, providing energy for your cells.
Research in 2024, led by Roberto Colleda and published in the Frontiers in Physiology journal, showed that around a week of no training sees mitochondrial enzyme activity slow down.
Between two and four weeks, there are more pronounced decreases in mitochondrial density and biogenesis (the formation of new mitochondria), leading to a decline in the ability of muscles to generate energy through aerobic metabolism. Basically, your diesel Ferrari starts its metamorphosis into a Sinclair C5.
As for your muscular strength, in the initial phase of detraining – around two weeks – it’s largely preserved, with neuromuscular function and maximal voluntary contraction showing minimal change.
Between two and four weeks, there’s a small reduction in power, particularly in the main cycling muscles such as the quadriceps and glutes. After that, it’s time to wave the white flag as your strength retreats.
Lowering of thresholds
How do these physiological reductions impact the key cycling metrics? “Both VO2 max and lactate threshold are impacted after around two weeks of detraining,” says Laursen. “It’s all tied in with that blood-volume and cardiac-output drop.”
VO2 max is your aerobic capacity – the maximum rate at which the body can transport and use oxygen during intense exercise.
The higher a rider’s VO2 max, the more oxygen their muscles can use, enabling sustained hard efforts. A 2000 study, led by exercise physiology guru Iñigo Mujika, revealed a 6% decline in VO2 max after four weeks of inactivity, which rose to 19% after nine weeks and up to 25% after 11 weeks. Not good.
As for lactate threshold – the intensity a cyclist can sustain for extended periods without unduly fatiguing – the closer it is to their VO2 max, the better for performance. A 2024 study showed athletes endured an average 20.3% drop after 56 days of no training.
But there is good news – for some, anyway. “If your lay-off is more down to life circumstances than injury, you can hold onto your adaptations with one or two high-intensity sessions a week,” says Laursen.
“It’s a similar idea to a taper [where you look to cut volume but maintain intensity in the last couple of weeks before your goal race]. We don’t want to lose that plasma volume or fitness. That’s where short high-intensity efforts come in.”
Laursen then waves a book at me – Interval Training for Cycling by Bent Rønnestad and team (independently published).
Within the 436-page tome, Rønnestad’s own research reveals that the 30/15 protocol, where you ride at high intensity for 30 seconds followed by 15 seconds of easy cycling, significantly enhances VO2 max, plus mitochondrial and capillary density.
“It works,” states Laursen. To integrate these into your (hopefully temporary) limited training time, begin with two to three sets of nine reps each, aiming for around 110% of threshold during the 30secs ‘on’ effort and 50% during the 15secs ‘off’ period.
Gradually increase reps and/or intensity over time. Just ensure you warm up, throwing in a couple of one-minute threshold efforts to wake up your system.
If you’re injured and cycling is off the menu, you have a couple more options. One is bloodflow-restricted training.
As the name suggests, this is where you restrict bloodflow via an inflatable cuff to stress the respective area in lieu of exercise.
Recently, I spoke to Dr Richard Ferguson of Loughborough University, who’s an authority on this topic. Ferguson told me it’s a proven tool to, if not maintain muscular gains, at least ameliorate the losses. However, be sure to seek an expert to administer the bloodflow restriction.
You could also try out Hytro’s recovery apparel, which is used by the likes of Tudor Pro Cycling and Deceuninck-Quick Step. It aims to achieve the same occlusion as inflatable cuffs but via a Velcro-fastening system.
Again, ideally seek expert help first. Failing that, you could simply get hot and sweaty. “If you’re injured, have a sauna,” says Laursen.
“As mentioned, plasma volume is key to maintaining fitness. By having a sauna every two or three days, you’ll hold onto plasma volume and won’t detrain as much.”
Return to performance
When it comes to returning from inactivity, you can take comfort in that 2024 research by Roberto Colleda (see above), who showed that the retraining process is around 30 to 40% faster than the detraining process.
So, if you’re off the bike for 20 weeks, you’ll be back at your pre-injury level after around 12 weeks. That said, it could be less, it could be more, because it depends on numerous factors – the duration of the detraining period, what activities were maintained during detraining, age and, once again, fitness.
“The fitter you are, the faster your return to peak fitness,” says Laursen. "It’s down to the plasticity of response.”
Essentially, this is the adaptability of tissues and the nervous system. The greater the plasticity, the quicker you recover.
“It’s something I delved into regarding altitude training during my post doc, many years ago,” Laursen adds.
“At the time, the literature didn’t see an accelerated response to altitude over repeated doses. However, anecdotally, that’s what climbers thought – that when they returned to altitude, they found it easier.
"So, we went to Nepal and walked up to Everest base camp and back a couple of times over a 10-day period.
"We showed that the second time was much easier. There’s a memory within the DNA, and that resulted in a better plasticity of response. It’s good news for the very active.”
Laursen again highlights that intensity helps in stimulating a faster recovery, albeit the ideal is to relay your aerobic foundations with long, lower-intensity, zone-two rides with one high-intensity session a week. “But ultimately, you’re the best judge of how your body and the injury are responding to training.”
Detraining is an unavoidable part of cycling, whether due to injury, illness or simply taking a break. Yet understanding how your body responds gives you the tools to mitigate losses.
With strategies such as targeted high-intensity sessions and sauna use, the decline can be slowed. Further good news comes via the plasticity of response, which means the retraining process is faster than the detraining process.
Just be mindful of Laursen’s final nugget: “When you’re injured, you realise endurance fitness is rented, it’s not owned.”
