Here are just some of the reasons why exercise is good for you:
- It helps prevent excess weight gain
- It reduces your risk of developing health problems such as a stroke, type 2 diabetes, depression, cancer and arthritis
- It stimulates various brain chemicals, which can make you feel happier and more relaxed
- It gives you a boost of energy, delivering oxygen and nutrients to your tissues that help your heart and lungs work more efficiently
- It helps you sleep better at night
But do the same rules apply when you're feeling under the weather?
Can you exercise when you're sick?
This is a surprisingly common question.
"Doctors are frequently asked 'Can I exercise?' by patients nursing a cold," says Dr Chng. "There are conflicting opinions on whether a person who is unwell should exercise. The answer really depends on two things: How sick are you? And what exercise do you want to do?"
Some experts suggest it is fine to exercise if your symptoms are 'above the neck', eg. if you have a minor sore throat, runny nose, blocked nose or can’t stop sneezing. If these symptoms diminish during the first few minutes of exercise, the intensity of exercise can be increased gradually.
On the other hand, if your symptoms are 'below the neck', eg. if you have a chesty cough, muscle or joint pain, fever, fatigue, diarrhoea or vomiting, then you may want to rest up instead.
Some experts also say that you should decide to exercise or rest based on whether you have a fever. As exercise raises your body temperature, it's possible that this could make a fever worse. In more serious cases, your fever could even cause an inflammation of the heart muscle – a potentially life-threatening condition.
Don't panic about this. In general, let your symptoms be your guide! If you feel miserable, you should take a break and rest. You should only start exercising gradually when you begin to feel better. When you do return to exercise, allow two days of below-normal exercise intensity for each day you were sick before resuming your normal training routine. If you're not sure, check with your doctor.
What types of exercise can you do?
Moderate exercise seems to help protect the immune system. During exercise, there is an increase in the production of cells that attack bad bacteria, like the ones that cause lung infections. The temporary rise in body temperature, which occurs during exercise, may actually help to stop bacteria from growing in your system.
In addition, if you have a blocked nose, exercise may also help to open your nasal passages and clear out some of the mucus trapped in there.
Conversely, repeated bouts of strenuous exercise can mess with your immune system. This is because your body produces 2 hormones, cortisol and adrenaline, during exercise. These raise blood pressure, elevate cholesterol levels and temporarily weaken the immune system. Studies have found that running a marathon, for example, can temporarily depress the immune system for up to 72 hours, during which you’d be more susceptible to infection.
So, stick to non-strenuous exercises that don't get you too hot and bothered such as:
- Outdoor walking
- Low-intensity bike riding
- Tai chi, qi gong or yoga
And avoid these activities:
- Heavy strength training
- Endurance training
- High-intensity interval training
- Sprinting or power activities
- Team sports
- Exercise in extreme temperatures
In short, do what you can do – and if you can't do it, then don't!