We're heading into cold and flu season now, so other than encouraging folks to keep their vaccinations up to date I thought to broach the subject of training when you are sick. This is a question that comes up with a good deal of frequency especially heading into the fall. There are a LOT of opinions on this subject and most research focuses on cold and flu. I'll do my best to summarize the research-backed verdicts here.
Before going any further, let me say this: never disregard the advice of your doctor. A trained medical professional who has examined you and prescribed your treatment will know the most about what ails you and how to best recover.
If you DO train when sick, do not do so at the gym or in a group setting as you will likely infect others. Viruses and bacteria travel through your breath, so you don't even need to cough in order to infect those around you. Do your training at home and/or on your own, where you will not share your illness.
Finally, eating a nutritious diet and engaging in regular physical exercise has a protective effect and boosts immunity.
HOW SICK ARE YOU?
The first thing you need to suss out is how sick you actually are. Understand that there are different levels of sickness just as there are different levels of hunger, tiredness and any other physical ailment or discomfort. Whether or not pushing through is the wisest choice depends on a number of factors.
An easy way to gauge whether or not you can participate in physical exercise is to use an above the neck/below the neck principle:
Above the neck means exactly what it sounds like: you have a stuffy (or runny) nose or sore throat. Mild cold or sinus/allergy symptoms fall into this category unless severe.
Below the neck means anything from fever and extreme tiredness to muscle aches, dizziness, shortness of breath, chest congestion, light-headedness, diarrhea, vomiting, swollen lymph glands etc.
Above all else, listen to your body before you decide to train.
HOW SHOULD YOU TRAIN?
Light physical activity such as walking, gardening, Tai Chi, gentle yoga, low-intensity outdoor bike riding etc (also employed during active recovery) should not cause a worsening of symptoms.
Moderate exercise such as lower-intensity (non-panting) outdoor cardio actually boosts the immune system provided that symptoms are not severe. Moderate exercise does not affect the duration or severity of the common cold.
Prolonged vigorous exercise has an immunosuppressive effect and should be avoided when sick. There have been instances of chronic fatigue syndrome developing and lingering for months or even years when athletes have continued training when ill without adjusting intensity.
If your illness is classified as above the neck and symptoms are mild, you may train as normal and still see the session as wholly productive.
If your illness is above the neck but has also moved into the throat, most of the time you can still train BUT you will have to dial your workout intensity and duration back especially if your nutrition is lacking, you are under a lot of stress or your immune system is compromised. Ways to adjust would be to do 1-2 sets of lifting instead of your normal 5, or walking or light jogging (or walk/jog intervals) for 20 minutes instead of the 40 minutes you were going to run.
If your illness is below the neck, rest, recover and sleep. If your nutrition hasn't been the best, get some healthy food into your system and let your body heal itself.
The below handy infographic was made by the folks at Precision Nutrition:
If you are using a decongestant, your heart rate will increase more rapidly than it would based on the intensity of the workout alone. This may cause shortness of breath and/or difficulty breathing. Dial back your training if taking a decongestant, or avoid all together.
If you have asthma and exercise while you have a cold your asthma symptoms may worsen.
Diabetics may have an issue as well because being sick causes an increase in blood sugar at rest as well as a decrease in blood sugar during activity. Diabetics need to monitor their blood sugar more closely when sick.
Other factors which affect how the body responds to exercise when sick include:
Age: our immune response can break down as we get older. The good news is that staying active and eating a nutritious diet can offset much of this effect.
Gender: Menstrual phase and oral contraceptive use may affect how the immune system responds. Estrogen usually enhances immunity while androgens suppress it.
Sleep: Poor quality sleep and/or prolonged sleep deprivation decreases immune function.
Training Age: The more often you exercise, the better your body will handle exercise when sick. As stated above, higher levels of fitness have a protective effect and may limit stress response to exercise.
GETTING BACK TO THE GRIND AFTER ILLNESS
Any significant lapse in training will cause a little fall back in your performance. After being sick, give yourself 2-4 weeks to build back up to the level you were training at prior to your illness. Be sure to give yourself extra rest, as even after symptoms abate your body is cleaning up the remnants of the virus or bacteria which knocked you out in the first place. Jumping back in too soon may cause the illness to relapse, and/or you may injure yourself because you've taken on too much too soon. As stated previously, listen to your body as you get back to your grind and be kind to yourself.