Between 2-4 Weeks: This is the timeframe where you lose a lot of hard-earned fitness. Over the first four weeks of detraining VO2 max can decline between 4-14%, and initially that’s mostly due to a reduction in maximum cardiac output (remember that reduction in blood plasma volume?).
You see this when you experience higher-than-normal exercise heart rates after a few weeks of minimal exercise. After the first three weeks or so, a decrease in your ability to extract oxygen from the blood also contributes to the reduction in VO2 max.
That decreased ability to pull oxygen from the blood is indicative of two other changes caused by a lack of exercise. After 3-4 weeks you see about a 3% decrease in red blood cell mass, which reduces oxygen carrying capacity. This is natural because your body adjusts red cell mass to your demand for oxygen; lower activity levels mean you can get all the oxygen you need from fewer red blood cells.
Your body also adjusts to the shift in resource demand with changes inside your muscle cells. Mitochondria are essentially the powerplants of your muscle cells, and they process carbohydrate, fat, and lactate into usable energy. One of the most important adaptations to endurance training is an increase in the size and number of mitochondria; and within 3-4 weeks of minimal training, you start losing that adaptation.
To make matters worse, the drop-off is greatest in the endurance-oriented slow-twitch muscle fibers, whereas your fast-twitch fibers retain their mitochondrial activity for longer.
Does Experience Slow Down Detraining?
Athletes often ask whether the 20 years of cycling they have in their legs changes the way they adapt to training and detraining. The answer is yes, experience matters.
Take the detraining-related losses of mitochondrial volume and power at lactate threshold. Compared to sedentary people and novice endurance athletes, after 8-12 weeks of minimal exercise, an experienced but detrained athlete will still have 50% greater mitochondrial volume and higher power at lactate threshold.
There’s also evidence that the capillary density that enables well-trained athletes to deliver oxygen to working muscle cells faster reduces from its peak density but remains elevated compared to non-athletes.
3 Steps to Avoiding Detraining
The way I see it, fitness has momentum. It takes time to create the adaptations that make you stronger and faster, and you can ‘coast’ through a short period of zero training before losing that momentum. But as you know from riding your bike, maintaining momentum requires less effort than gaining it, and the same is true with fitness. Holding on to what you have is easier than you may think, and it’s certainly easier than starting over.
Step 1: Reduce frequency. You can reduce your number of weekly rides by about 30%, which means a rider can go from riding 6 days a week to 4 days, or 4 days to 3.
Step 2: Reduce volume. For most people, this goes hand-in-hand with reducing frequency, but the point is that you don’t have to make your rides longer in order to compensate for reduced frequency.
Step 3: Maintain or increase intensity. This is the critical part. You have to give your body a reason to keep your performance markers from falling, and intense efforts provide the stimulus necessary. That doesn’t mean you have to do 3-4 days of structured VO2 max intervals every week to keep from detraining; I’d recommend 1-2 interval workouts, one longer endurance ride with some strong climbing efforts, and one fun and hard group ride. And the biggest takeaway here is that lollygagging along isn’t going to do you any favors if you’re already experiencing reduced training frequency and volume.
To return to my preferred method of positive reinforcement, the opportunities here are that you can avoid a significant drop in performance pretty easily, even with postponed events and potential restrictions, and that you can set yourself up for big performance gains when the season resumes.