Often times I get asked, “just how long can I rest while I recover from my injury/illness, before I start to lose my fitness level”?  All of us are hesitant to give up the gains we have made from all of that training. Although this isn't a straightforward question, there is plenty of enlightening research on this subject.

For the sake of clarity, we should first define the concept of “trained”.

For our purposes, let’s just say that a trained individual is a person that regularly (3-4 x a week) engages in physical activity that results in a sustained aerobic training heart rate for a period of 30 minutes or more. In other words, the concepts herein regarding deconditioning will only apply to people that have been exercising fairly consistently and diligently over a period of at least a few months.

The phenomenon of losing fitness (otherwise known as deconditioning) when one discontinues exercise is among one of the five main principles of conditioning. Basically, the principle of Use/Disuse says that your body gets stronger with exercise and will weaken without it (“use or it or lose it”).

It seems the going wisdom among athletes is that when one stops training, it all goes to pieces in a rapid manner, which of course leads to people insisting on training through various injuries and illnesses. Fortunately, the evidence suggests that we only lose fitness about as quickly as we gain it. 

In general, researchers conclude that after a 2-week hiatus from training, the typical decrease in fitness gains may be expressed as:

• VO2 Max decreases 5-7%
• Lactate threshold: decreases
• Blood Volume: decreases
• Flexibility: decreases
• Heart rate increases 5-10%
• Stroke volume (how much blood is pumped with each beat): decreases 6-12%
• Muscle glycogen stores decrease by 20-30%

Interestingly, the deconditioning studies have shown that endurance performance will actually stay the same or even increase slightly after a few days off; this is probably due to continuous training that contributes to some degree of continual fatigue.

A few days rest in this case allow the body to catch up and fully recover. But after a few days, we begin seeing declines in the measurable parameters mentioned above. Once that 2-week rest period continues, one may expect continued declines in performance of 3-5% after another week or two off. 

Cutting Back

The good news in this is that nearly peak levels of fitness can be maintained for a long period of time even when training frequency (number of times per week) or duration (time period of exercise bout) are decreased. This of course comes in handy when one is injured or overly fatigued. The key here is that intensity must be maintained, however. 

When intensity of training is reduced, and overall volume of exercise is maintained, fitness will decline more rapidly.  What this means is that when one is cutting back on training, the best way to hold onto a certain fitness level is by holding the intensity of training, while reducing the overall volume of training. This is where cross training comes in. Training in another discipline with the same intensity will keep you fit while you take a break from one sport. 

Cross training is a good answer only if one can perform some type of activity that does not aggravate the original reason for a taking a break, of course. Before plunging in to a cross training program (if you are injured), check with your physician to make sure you are making a smart choice. 

However, if you're acutely ill, it's important to just straight up rest and give your body the space it needs to fully recover.  Exercising through an illness will almost certainly prolong it.  The time you end up taking off now, and letting your body get well, won't nearly approximate the decrements in training and the possibility of getting even sicker (and then taking more days off) if you continue to train through an illness. 

So, the answer to our original question of “how long can I take off before I lose my fitness level” is that it depends. It depends on your current level of fitness, and how long you rest, and exactly how you rest. But, the general take away is that you will lose your level of fitness about as rapidly as you gained it. For most of us, a week off here or there may actually be a good thing, and not as detrimental to our fitness and training as originally thought. 

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