Sickness! What about training?

You're following your <insert race distance> training program and everything is going great!  Distance is increasing and workouts are getting easier.  Then along comes a sniffle.  At what point do you slow down?  How will it impact your training?

This happened to me back in August during my Philadelphia Marathon training.  I was three months out from the race and had a 14 mile run planned.  Leading up to the run I had a fairly nasty head cold.  I had to choose, run with the cold or skip the run?  Even though I felt bad I decided to complete my the run.  This was one of my most miserable runs ever.  The run ended up turning sinus congestion into chest congestion and making me sicker.  I had to take a week off from training just to recover.

Flash forward to last week.  Again, I had a head cold and something going on with my eyes.  Since it was fairly cold in New York City last weekend, I decided to skip the long run.  I completed my shorter in-week runs on a treadmill.  (I was travelling for work so indoor track was out of the question).  This was much better for me.  Instead of worsening the cold, I missed one 10 mile run and one 3 mile run.   My training wasn't severely disrupted and I'm ready to tackle this week's long run.

Its not easy to make up missed runs without inflicting injury.  So I generally just pick up with the next week in my training plan.  If I'm not quite ready for the length of the suggested long run, I'll cut a mile or two off.  Its important to do what feels right for you in training while being comfortable that you can meet your goals.