I've noticed the exact opposite myself, and I've actually managed to take advantage of it sometimes.

I climb rocks, and a few times I've had days where, for no reason I could explain, I have performed far above my normal abilities (1). Big days, where I've sent routes that were way above my head. Routes that I couldn't pull individual moves on when I came back to them a week later.

Then the next day I would be clobbered by a cold so violent that I'd be bedridden for an entire day.

I chalk it up to the body knowing that a cold is on the way and storing up all the immunities, defences, and reserve energy that it will need to fight it. If you time it right, you can steal all that stuff and channel it into one day of hard climbing. Of course then when the cold does come, the body has nothing to fight it with so you get crushed.

Considering how good it feels to be that on form, even just for a single session, I think it's actually worth it.

(1) If you climb, you'll know that it's a very measurable sport. If you can boulder a certain grade, you can get on a given problem and have a reasonable expectation of being able to work it out. Or alternatively, you can know for a fact that you could train on this one particular problem for an entire year and never top out. So when you're having a day like the one I describe above, it's the equivalent of showing up at the gym one day and finding you can suddenly bench press 50 pounds more than yesterday.

Important caveats: 1/ Too much exercise increases the chances of catching a cold as well as increasing the severity (there is research on this) 2/ Gyms are full of people and you touch a lot of the surfaces - so that may offset the effect (this I'm guessing)

People who exercise are more likely to eat healthy and take care of their body in other ways.

Did they people who made the study correlate for that?

I would personally vouch for it. Not just cold, I have got rid of nagging headaches and other ailments too after starting on a regular exercise regime

> Lead researcher Dr David Nieman and his team, from Appalachian State University in North Carolina, say bouts of exercise spark a temporary rise in immune system cells circulating around the body that can attack foreign invaders.

This makes an interesting contrast with other recent reporting on colds and the immune system, such as http://www.nytimes.com/2010/10/05/opinion/05ackerman.html?_r... which says (correctly, AIUI) that the immediate cause of cold symptoms isn't the infection itself but the body's immune response to it.

Resolution: http://blogs.plos.org/bodypolitic/2010/10/06/how-not-to-figh... -- a more active immune system at the moment of possible infection may help you not get infected, but a more active immune system while you've got the infection may make things worse. (And: "the immune system" is a complicated thing, and the bits of it that make a cold worse may not be the same as the bits that make you less likely to get one.)

This is actually a little paradoxical, because numerous reports have shown that strenuous exercise depresses the immune system by increasing glucocorticoid levels. The odd thing is that glucocorticoids cause an increase in circulating neutrophils, but some think that they are actually less available to fight infection, because usable neutrophils are found lining the postcapillary venules. All told, studies of the cold paint a complicated picture.

Interestingly, the immediate aftermath of a workout is suppressed immune function. (http://jap.physiology.org/cgi/content/full/82/5/1385)

But it does seem reasonable that someone living the broadly healthy lifestyle of a person who gets a good amount of exercise would also find themselves less susceptible to colds etc...

Seems kind of obvious, exercise strengthens the body and promotes general health. What next? wrapping up warm can prevent a cold? Slow news day?

I can verify this as I was the super sickly kid at high school. When winter arrived, so did the illness period for me. Then I started practising some martial arts in university and my immune system got pretty strong. Hardly had any critical illnesses since then.

When I have a cold (sneezing, coughing), I go running anyway (like I do almost every day) and I feel much better for the rest of the day; most of the symptoms disappear, even when running in winter :)

Being healthy requires the combination of a good diet, adequate clothing that suits the weather and exercise.

To add my own anecdotal evidence: I have experienced the same relationship.

Cleaning your hands when you get back home after having been outdoors - a very basic hygiene measure - does a WHOLE LOT more, I would say. Interestingly, in contrast to the article, the direct effect of a session of physical activity is a short suppression of the immuno system that leaves you temporarily more sensitive to the rhinovirus, should you be carrying it at the time.