Should You Run When You’re Sick?

When you're feeling sick but really don't want to miss out on valuable training, it can be challenging to know whether to curl up in a little ball on the couch or suck it up and head out on your regularly scheduled run. What to do? When you feel like you're fighting off a bug, is it better to choose complete rest, or to “sweat it out”?

Your immune system is responsible for fighting off diseases and keeping you healthy, and its function is greatly influenced by stress. Short bursts of stress (lasting from just a few minutes to a couple hours) can actually help boost overall immune health, but chronic stress (lasting days or even years) can have very detrimental effects. By “stress,” we’re not just talking about those busy days when you want to pull out your hair and scream at your boss (although that certainly counts too), but anything that places an extra burden on the body, such as:

• Physical stress, like exercise or physical labor
• Psychological stress, such as those from finances, school, career, or relationships
• Lifestyle stress, like poor nutrition, drugs, or bad hygiene
• Environmental stress, such as extreme heat or cold, pollution, or high altitude

Exercise is a type of physical stress, and that stress influences immune function. When you’re healthy, your body can easily adapt to the stress that exercise places on the body. In fact, this adaptation is what makes us stronger and healthier.

When you’re sick, however, your immune system is already stressed. The added stress from a hard workout — like a long run or a tempo workout — can be more than the immune system can handle. One single high-intensity workout or long run can depress immune function. This means you’re not letting the immune system do its job, and this can prolong illness or even make you more sick.

So does this mean you’re doomed to lay on the couch like a slug every time a case of the sniffles comes on?

Not necessarily.

Think of exercise as a spectrum, ranging from non-strenuous movement to tough, purpose-driven workouts. On one end, you are moving your body without much physical exertion — in other words, you’re not placing a great load of stress on your body. At the other end of the spectrum are strenuous workouts — their whole purpose is to stress the body in order to make gains.

If you’re feeling under the weather but don’t show signs of fever or body aches, easy movements are probably fine. They may even be helpful. Remember, this means limiting yourself only to activities that aren’t intense enough to create immune-compromising stress. This will vary from person to person depending on fitness level, but non-strenuous movement could include:

• Stretching or foam rolling
• Easy yoga
• Walking
• For those with high levels of restraint and fitness, a very easy jog may be tolerated

If you’re feeling downright crummy, or have a fever, elevated heart rate, fatigue, vomiting, diarrhea, muscle and joint pain, or a deep cough, then for goodness sake, take some time off and just rest. It takes about 10 days before you’ll lose significant running fitness, so as long as you don’t make a habit of it, there’s no need to panic if you need to take a few days off.

• Assess your symptoms. If you have a fever, elevated heart rate, extreme fatigue, vomiting, diarrhea, muscle and joint pain, or a deep cough, opt for complete rest. Consult a healthcare professional for further guidance and treatment.
• If your symptoms are minor, opt for non-strenuous movements.
• If you’re feeling lousy and just don’t feel like doing anything, don't force it.
• Be patient and err on the side of caution.
• If you do run while you’re under the weather, it should be about maintaining fitness, not advancing it. Keep things easy, skip the intervals, and put an extra emphasis on getting plenty of sleep and high-quality nutrition.
• If you head out for a run and feel like garbage, abort the mission and go home. You’re not doing yourself any favors by pushing through and running your immune system into the ground.
• Stay out of the gym. No one wants your cooties.

Once you finally start feeling healthy and human again, you’ll probably be itching to get out for a good run. It may be tempting to try to “make up for lost time” and stack in several solid workouts, but it's very important to resist this urge!

As frustrating as it may be, you need to respect the health of your immune system. It’s best to wait a full 24 hours after you start feeling normal again before you resume training. Once you do begin running again, ease your way back into it. Your immune system probably isn’t quite back up to speed yet, and the last thing you want is to relapse into illness again. Spend your first few days back doing easy, short mileage runs. After two or three days of easy running, you can try a more structured workout or longer run. Continue to listen to your body, and back off if you feel the return of any symptoms.