One of the most common questions I get from my athletes is, “Should I come in to train when I’m sick?” The easy answer is usually no, and with some illnesses, it’s pretty clear whether you should be taking it easy. But when that illness is a cold or an upper respiratory tract infection, the answer is actually a little more complicated. After all, a runny nose isn’t the same thing as a fever and vomiting.
 
So that’s when the bargaining begins. “But I feel like I’m over the worst of it...” “I can at least squat…” It’s instances like these where science is a coach’s best friend. For those in the TL; DR crowd, here’s the bottom-line up front: Science says you probably shouldn’t do high-intensity workouts like weightlifting or CrossFit when you’re feeling any sort of symptom of a cold. Instead, wait until you feel 100 percent better before you dive back into your typical programming.
 
The common-sense reasoning behind this is that when you perform vigorous exercise, you are breaking your body down in order for it to repair itself stronger. When you have a cold, your body is already working hard to eradicate the virus, so when you work out, you’re now asking it to pull double-duty, which usually ends up in you getting sicker. Weightlifting is especially taxing on the body given the load and intensity at which it is performed. After all, it isn’t twenty minutes on an elliptical while sipping a latte and reading on your iPad.
 
But really, without some actual studies to back that up, a lot of that can just come off as a mere generalization mixed with anecdotal evidence and a whole lot of assumptions. Gross. So, here’s what peer-reviewed articles had to say about this. A review of many studies explains that “prolonged bouts of strenuous exercise cause a temporary depression of various aspects of immune function that usually lasts ~3-24 hours after exercise, depending on the intensity and duration of the exercise bout.” The review added that “postexercise immune function dysfunction is most pronounced when the exercise is continuous, prolonged (>1.5 hr), of moderate to high intensity (55-75% maximum O2 uptake), and performed without food intake” and this dysfunction “may compromise resistance to common minor illnesses such as URTI.”  
 
Here’s the simplified version of that: if you work out hard, it may make you more likely to catch a cold. If you already have a cold, you’re weakening your immune system, which puts you at risk of getting even sicker than you already are.
 
What’s stated above, however, focuses on high-intensity exercise. Another study suggests that low-to-moderate exercise training during a rhinovirus-caused upper respiratory tract infection doesn’t appear to affect either the severity or the duration of symptoms of illness. In this study, subjects were injected with a virus (there are some researchers not too thrilled about that, I’m sure), and one group exercised while the other group did not. The exercise consisted of moderate cycling on an Airdyne bike, walking or jogging on a treadmill, or stair-climbing. The subjects who exercised seem to share very similar durations and severities of the cold as those who didn’t exercise, suggesting that anything up to moderate exercise won’t actually hurt you.
 
Weightlifting and CrossFit aren’t walking on a treadmill for 20 minutes, though. While I wish there were studies about the effects higher intensity exercise with a cold, I have felt the existing studies provide sufficient data for me to tell my athletes to take it easy. If they complain about that, I offer for them to hop on the assault bike at a moderate pace for twenty minutes. Most opt for the rest day.
 
The rule I have for my athletes is to wait until they feel better and then wait at least one more day before coming back to training. It’s also a rule I follow myself. The reason for that extra day is that athletes will often convince themselves that they’re okay when they’re actually still recovering. I’ve done it before, too—thought I was all better, went in to train, and then found myself laid up in bed for the next three days.
 
If you’re sitting around sick, and you feel as though missing out on training sessions will somehow make you lose your edge, just know that taking care of yourself is part of your training. Rest up, recuperate, and when you’re better, get back to work.