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Exercising when sick: yes or no?


You’ve probably already noticed that regular exercise strengthens the immune system, meaning you’re less likely to get sick. However, this doesn’t mean that you’ll never get ill even if you train. Whether it’s the flu, stomach ache or a migraine, even the most resistant athletes succumb to illness occasionally. But how should this affect your workouts? And is it ever okay to train through the pain?

HIIT and the open window

When it comes to easy and moderate sports, continuing to exercise while you have a slight cold can have a positive effect, but this isn’t the case for HIIT. HIIT is a physical challenge that relies heavily on your immune system. If you train when sick, the functionality of the immune system will be restricted. The pathogens can therefore continue to spread unhindered. The result: after a workout you are sicker than before. This effect is also referred to as an “open window”. So take care to keep that window closed by staying in bed and resting.

How long should I rest for?

With slight illnesses such as a mild cold or a runny nose you can start exercising as soon as the symptoms are completely gone – not when you feel good again but when no more residual symptoms appear.

With feverish diseases or infections that require the use of antibiotics, the training break extends not only to the acute phase. The risk of a bacterial or viral infestation of the heart muscle is further increased then. Even if, subjectively, you already feel fit again. In most cases the disease lasts longer than the symptoms involved – especially when symptom-relieving medicine was taken. The immune system is still in a weakened state and needs time to regenerate fully.

This particularly applies to the use of antibiotics because they do not distinguish between harmful and beneficial bacteria and further weaken the body. It is generally advisable to wait for at least the same period over which the medication was taken. For example: when taking antibiotics over a period of six days, you have to wait a minimum of a further six days before returning to exercise. The body’s defense not only needs time to recover from the infection itself, but also from the effect of the antibiotic.

Similarly with fever: an increase in body temperature is an extreme measure of the immune system. When you return to a normal temperature, this does not mean the illness is finished but only that the worst is over. The fight against the pathogens continues at full speed, so generally, you should pause training for at least another week after the last feverish day.

However, it is important to remember that the main rule is still to consult first your doctor about how long you should rest for.

Let’s recap:

For those who simply cannot wait until the end of the rest period, it is important to know that a weakened body hardly reacts to training stimuli. So take your rest with a clear conscience, increase the workload and the intensity thereafter slowly and moderately, and after a few days of acclimatization you’ll be back to your usual routine.