Should you exercise while sick?

The colder weather has arrived here in Australia, and with that comes the winter sniffles. Yep, cold and flu bugs are in the air, and ready to strike! While many people are happy to use winter illnesses as a good excuse to stay in bed for a few days, some people aren’t happy to take a break from their regular exercise regime, and would prefer to “push through and sweat it out”. So, is it a good idea to keep on exercising while you are sick, or should you head for the couch with a nice warm blanket?


Infections can be caused by both viruses and bacteria, which are both commonly known as pathogens. Different strains of viruses and bacteria can infect the body in slightly different ways; meaning the symptoms you suffer can vary depending on what is causing the infection you have. The easiest way to tell the difference between a viral infection and a bacterial infection is the colour of the mucus you cough up or blow into a tissue……viruses will result in clear mucus, while bacterial infections result in a yellow/green colour. It is worth understanding that some infections start out as viral, but soon develop a secondary bacterial infection.

Upper respiratory tract infections (URTIs) are infections limited to the sinuses and throat. These infections usually result in irritated and blocked sinuses, and a sore, scratchy throat (often resulting in a cough). Headaches and sinus pain are also common, with more severe infections causing fatigue and a fever. With an URTI, you will find yourself blowing your nose on a regular basis. A good example of an URTI is the common cold.

Lower respiratory tract infections (LRTIs) affect the lungs. These infections can cause chest pain and tightness, and often result in breathing difficulties. Coughs are pretty much guaranteed with LRTIs; and like URTIs, more severe infections can result in fever and fatigue. Pneumonia and bronchitis are examples of LRTIs.

Influenza, or the flu, is a more severe viral infection that affects both the upper and lower respiratory tracts, causing sinus and chest congestion, headache, chills, fever and body aches. In some individuals, the influenza virus can be a serious health risk……sometimes resulting in death.

As already stated above, different types of viruses and bacteria can affect the body in different ways….so your symptoms may vary, depending on which pathogen has decided to invade your body.


Your immune system is responsible for fighting any infections that invade your body. We have two types of immune defence systems….the innate immune system, and the adaptive immune system.

The innate immune system is the first line of defence. It involves physical barriers, such as our skin and mucous membranes; chemical barriers such as saliva and our stomach acids; and protective killer cells which attack anything they recognise as foreign. Unfortunately, many viruses and bacteria can overcome our innate immune system, which is where out adaptive immune system kicks in.

Without getting too technical, the adaptive immune system recognises the cells of viruses and bacteria, and begins to produce specific cells to attack these pathogens. It can take a couple of days for the body to recognise, react, attack and destroy foreign cells, hence most infections last for about a week…..depending on the severity of the infection of course!

The immune system also has a “memory”, so it remembers the structure of individual viruses and bacteria. Hence, when your body is invaded by pathogens that it has seen before, the body is better at fighting them, as it has dealt with them in the past! This is basically how vaccines work….but unfortunately, many viruses and bacteria evolve, so the body has to react to these evolved pathogens as if it has never been exposed to them.


For those who exercise on a regular basis, you will probably know there is a big difference between non-strenuous activities and intense workouts. Both have different effects on the body; and both can affect the immune system in different ways.

Lower intensity, non-strenuous exercise has been shown to increase the function of the immune system….and regular moderate exercise also strengthens the immune system. However, sessions of high intensity exercise can actually have a negative effect on the immune system. Our bodies can be more susceptible to infection for up to 72 hours after these types of sessions, due to a slightly suppressed immune system.

Unfortunately, this is why many athletes get sick on a regular basis. Those who exercise a couple of times a week at a low intensity have the advantage of their immune system being improved. But those who perform high intensity training on a regular basis can actually lower their immune system……being at your peak fitness can mean you get sick more often!


There is no strict rule which you should be following in regards to exercising while sick. Depending on who you speak to, you may receive slightly different advice……this is my  personal advice as a pharmacist and an athlete.

As a basic rule of thumb…if the symptoms you are suffering are limited to the sinuses and throat, its okay to head out and still do a little bit of exercise. However, you should keep your activities to a low intensity, as any higher intensity exercise can cause additional stress to your body, which will mean your immune system may suffer… your infection may last longer or turn into something worse!

Chest infections, body aches and/or a fever can mean something a bit more serious….its a good idea to rest up or a couple of days to allow your body recover. Let your immune system do its thing, and ease back into exercise gently over the course of a few days once you start feeling a bit better.

It is also worth remembering that any exercise can lead to dehydration if you don’t drink enough……so if you decide to continue being active while sick, be sure to keep your fluids up to help your body recover. If you have a fever, you will possibly be a little bit dehydrated already… the best idea is to put your feet up and rest!

As I have stated in previous articles, listen to your body! If you aren’t sure whether you should head out or not, its probably best to put the running shoes away or keep the bike in the spare room……head for the couch and give yourself a bit of time to feel better!

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