head coldThe relationship between exercise and immune function is not as straight forward as many believe. Certainly, most scholars have concluded that a history of regular exercise is associated with increased life expectancy and decreased disease duration when compared to outcomes experienced by a sedentary population. Therefore, it is probably safe to conclude that among the many benefits of regular exercise is enhanced immunity over time, and that individuals who wish to strengthen their immune systems as a precaution against disease and infection should participate in a regular exercise program.

In the short term, however, the literature yields mixed conclusions about the relationship between exertion and immune function. Some studies seem to suggest that as a result of the physiological stress imposed on the body by strenuous exercise, a difficult workout actually opens a brief window (somewhere between 3 and 24 hours) where viral and bacterial infections may gain a foothold and manifest into illness. Other studies have failed to confirm this hypothesis. “Vulnerability window” or no, repeated anecdotal studies have found that perception of immune function does vary predictably by exercise intensity. In other words, among people who are already feeling ill, moderate exercise seems to lessen the symptoms of illness and infection while strenuous exercise appears to make symptoms worse. This pattern is particularly clear in the literature surrounding exercise and the common cold, and when viewed through the lens of “exercise as physiological stressor,” makes perfect sense. The more stress imposed, the worse an already ill body is apt to feel.

Based on this information then, what clues can we take to guide our exercise behavior during cold and flu season?

  1. If you feel a cold or flu coming on, rest is probably your best bet. If, however, you wish to exercise, attenuate the intensity to avoid the “vulnerability window,” should one in fact exist. Depending on your fitness level, this could take the form of a brisk walk, light jog, or low-intensity circuit workout.
  2. Once you are already ill, all signs point to avoiding strenuous exercise. Not only does strenuous exercise seem to be correlated with an increase in unpleasant symptoms, but common sense dictates that none of us are as coordinated or energetic  once we are under the weather. Steer clear of Crossfit, heavy  lifting, intense metabolic training, sprint intervals and the like, and for that matter, don’t stress about taking a day off. The gym will still be there once you are back on your feet.
  3. Finally, if you do choose to exercise while you are ill, please remember that your fellow group exercise classmates and gym-goers would prefer not to share in your plight. This goes for your trainer as well. If you are feeling under the weather, please stay home.  A body weight circuit workout in your living room will be just as effective as heading to the gym, where someone else may pick up whatever you’ve come down with. If you choose to walk or jog, please take your workout to the streets as opposed to the treadmill, and remember to cover your cough.