It's a well-worn cliché that doctors make the worst patients; it would be an easy leap in logic to add that so do runners. I'm usually fortunate in that I rarely get sick, thanks to a combination of genes, a solid fitness regime and a high nutrient diet which wards off the worst evils.
It's inevitable though that even the fittest of us fall ill occasionally, and when I do I'm not a happy camper. Cue dramatic back slap of hand to forehead and assumption of long-suffering expression as I took to the couch with a post-Christmas cold and a big box of hankies.
There is a fine tightrope to be walked in fending off winter colds and viruses. People who are fit and exercise aerobically several times a week are less likely to catch a cold, and their colds tend to be milder than for those who don't exercise. Great, I hear you say!
On the other hand, this benefit tapers off over a certain number of hours of exercise a week, and partaking in high volumes of endurance training (for example, Ironman or marathon training) increases levels of the stress hormone, cortisol, which in turn will weaken the immune system and tend to lead to more illness.
If you are putting in long hours of training but are constantly picking up colds or viruses, it may be a warning shot that your body is struggling to manage this load.
Sometimes of course, with all the fitness, kale and organic blueberries in the world, picking up a winter cold or bug is inevitable - so the question is: to exercise through it or not?
The general wisdom is that if a cold is 'above the neck' (runny nose, sneezing etc), then you can train at an easy level, but if you have a temperature, a sinus infection or 'below the neck' symptoms (coughing or sore throat), then it's advisable to rest until the symptoms go away.
My personal experience is that once a cold settles in, exercise usually makes me feel great temporarily, and then exacerbates all my symptoms until I grind to a halt.
While it varies from person to person, the best remedy is to firmly apply a little common sense (something that mid-season runners and triathletes are often severely lacking in).
If you're wiped out with fatigue or running a high temperature, take time off until your symptoms improve and then start back training at an easy level until your immune system is fully recovered.
And if you're contagious - stay at home; the rest of us will thank you for containing your germs so we can keep running!
Tissues, cough syrup and a whole phalanx of other cold remedies in hand, it was a sorry start to a new year of running personal bests.
Switching from the tempestuous Irish winter weather to a sunny northern California to return to work didn't help to clear my clogged up head and lungs, and I spent the weekend with my face longingly pressed against the window, wishing between trumpeting nose blows that I was outside at play.
With an annoying cough, there was no point in trying to improve my fitness until it lifted.
On Sunday, feeling a bit better, I cautiously headed out for an easy hour on my bike, but was repaid later with sinuses full of cement.
As if by magic, on Tuesday the cold and cough lifted and I was ready to get back in action. I joined the weekly Silicon Valley Triathlon Club track session at Foothill College, dialling back the effort level substantially so that I didn't overload my lungs.
Despite a cold-husky voice to rival Barry White, I cruised around a decreasing pyramid interval set at 75pc of my usual track effort, and boy, did it feel good to be back!