Last week I exercised myself sick.

I was feeling pretty good; then I went to the gym, pounded out a tough, full-body workout, jumped on the treadmill and sprinted for about 10 minutes, stretched, went home, and got sick.

It wasn't the first time:  last summer, when prepping for a triathlon, I panicked last minute about my prep and did the bike-run portion of the race at 100% capacity two days before the race.  My time that day was great.  My health, on race day, was awful. 

What happened in both cases is that I pushed hard though an all-out endurance-style workout and felt a feverish feeling afterwards that never really went away till a couple of days later.  In one case, it probably cost me a medal. 

I was starting to think that my brushes with exercise-induced illness were unique to my physiology till a client of mine pointed me to this article in the Times, which suggests that if you're verging on sick, hard exercise is a bad idea:

The bulk of the new research...reinforce a theory that physiologists advanced some years ago, about what they call "a J-shaped curve" involving exercise and immunity. In this model, the risk both of catching a cold or the flu and of having a particularly severe form of the infection "drop if you exercise moderately," says Mary P. Miles, PhD, an associate professor of exercise sciences at Montana State University and the author of an editorial about exercise and immunity published in the most recent edition of the journal Exercise and Sport Sciences Review. But the risk both of catching an illness and of becoming especially sick when you do "jump right back up" if you exercise intensely or for a prolonged period of time, surpassing the risks among the sedentary.

So, apparently, is no exercise.  Moderate exercise?  Right in the pocket. 

These data underscore some facts that many of us already know:  exercise is a stressor, like injury.  Indeed, the body's immune response to a hard workout is pretty much indistinguishable from its response to mild injury.  Perhaps--though I'm armchair immunologisting right now--if your immune system is already overtaxed, then a hard workout may be enough of a distraction to allow flu germs to take hold.  A mild workout, however, "gets the blood flowing," and enhances immunity, so that you might nip flu in the bud before it takes hold.

Either way, the data seem clear enough:  if you're feeling like you're coming down with something, back off, there, Steamboat.  Do something easy and enjoyable and you're less likely to be down for the count in a few days.

Have a gooooooood weekend!

Andrew