Detraining happens quickly
The human body doesn’t like to maintain anything it doesn’t need. That’s why, as soon as you stop training, your body starts letting go of the fitness you built up. A short period without training lasting a week or two is not a big problem. It can even be beneficial if you do it right. But after two weeks of inactivity, you will start losing your fitness very rapidly.
It starts in the first week
The first thing that happens when you stop training is your blood plasma volume starts dropping. This reduces your cardiac output and your ability to control temperature through sweating. The glycogen stores in your muscles also start to decrease. Even though these adaptations start declining quickly, already in the first week, the good news is that they also return quickly when you start training again.
Things accelerate after week two
You should really start worrying when you’ve been away from training for more than two weeks straight. This is when you start losing things that won’t come back quickly when you start training again. Your VO2 max can decline by 4-14 % in the first month. You start seeing much higher heart rates with the same intensity levels. Your ability to extract oxygen from blood also decreases.
It gets even worse after a month
When a month goes by without any training, your blood cell mass will start dropping. It can be as much as 3 % in the first month. This further reduces your oxygen-carrying capacity. Your body simply doesn’t need as big of an oxygen supply so fewer red blood cells are enough to do the job. You also start losing one of the most valuable training adaptations for endurance athletes – the size and number of your mitochondria, the powerplants of the cell that produce energy for your legs to pedal.
It’s clear to see that taking 1-2 weeks off is probably not a big deal if you return to training – you will quickly gain back what you lost. Taking a longer break is when things really start declining. This series will go over strategies that can help you maintain fitness through a longer break with minimal effort and it will show you how to best restart training if a longer break is necessary.