Colds and flu

Updated 18 September 2019

Exactly how can flu damage your heart?

There is a reason why you shouldn't exercise when you are suffering (and even recovering) from flu.

We know the rules – when you're sick, it’s better to rest than to risk it, especially if your body is fighting an infection.

Fighting off a virus

More serious than the common cold, the influenza virus places a great deal of strain on your body, and it's not without reason that doctors will advise you not to exercise when you have the flu. The main reason is not because you feel generally lousy, but because your heart has to work harder to fight off the virus.

You will usually experience other signs that your body is working overtime – including a fever. When your body temperature is elevated, your heart beats faster to get the blood delivered to your organs. When you then place extra pressure on the heart, it can cause an irregular heartbeat that might irreversibly damage the heart muscle.

How to spot strain on your heart

Flu can also lead to a condition called viral myocarditis, which is inflammation of the heart muscle. While myocarditis seldom becomes fatal, it can under certain circumstances be dangerous for even the healthiest, fittest individual.

People who have generally healthy hearts might not even realise that their heart muscle is damaged, and it might only cause trouble if you do strenuous exercise during a bout of flu. Symptoms of myocarditis can include:

  • Fatigue
  • Breathing difficulties
  • Abnormal heart rhythm – often with fainting spells
  • Chest pain, which may mimic a heart attack
  • Inability to lie flat because of shortness of breath
  • Leg swelling
  • A preceding viral illness
  • Fever
  • Joint pain and swelling; headache

If you experience any of these symptoms during or shortly after a bout of flu, it’s imperative that you see your doctor immediately.

So, when can you exercise safely?

Those of us who had the flu during the winter months might be wondering when we can safely return to our normal workout routine after taking things slowly.

According to Jenny Hadfield, a running coach and author with over 20 years of experience, a good rule of thumb is to invest in a day of rest for every day you were down with flu symptoms – for example, if you experienced five days of symptoms, you should be taking five days off.  A good sign that your body is on the mend is when you no longer have a fever.

Another rule of thumb is to listen to your body and your resting heartbeat. On the day of your race or training, wake up and take stock of how you feel in general. If you still have symptoms located below your neck (phlegm on your chest, muscle aches, fatigue, an upset stomach); if your resting heartbeat is higher than usual; or if you feel generally lousy, it’s best to carry on resting.

Also listen to people when they say something like: “There will be many more races, but there is only one of you!” While this kind of advice might be frustrating, it's ultimately better for your health.

Image credit: iStock


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Flu expert

Dr Heidi van Deventer completed her MBChB (Bachelor of Medicine and Bachelor of Surgery) degree in 2004 at the University of Stellenbosch.
She has additional training in ACLS (Advanced Cardiac Life Support) and PALS (Paediatric Advanced Life Support) as well as biostatistics and epidemiology.

Dr Van Deventer is currently working as a researcher at the Desmond Tutu Tuberculosis Centre at the University of Stellenbosch.

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