So the question is what should you do.
- define sick? under the weather, tired, hacking up a lung, fever, minor sniffles ...the degree of illness does matter.
I like the "neck rule" for starters. Symptoms below the neck (chest cold, bronchial stuff, body ache) require time off vs above the neck (runny nose, stuffiness, sneezing don't pose much of a risk if you keep training. That being said even if above the neck, it maybe wise to dial it back, go aerobic for the day and see how you are tomorrow. The risk is that the "above" the neck cold escalates into a lower respiratory infection and than you are looking at days off.
I also like the really scientific approach of a "gut check". If you are 100% honest with yourself (not thinking about an upcoming race/your competition/your sub par workout last week) how do you feel? Do you want to go out and crush it training or are your worried about missing a day so feeling like you SHOULD train? Any triathlete most are very fine tuned to their body and knows when something is OFF. so think about how you really feel.
Many times we (athletes and I) agree to 1 or 2 day's off and then they are back crushing it later in the week- maybe it was just necessary recovery. Being able to back off or skip a workout occasionally when something is not right will allow you to keep training.
We all have little voices in our heads. Come admit it. ( I have many)
And then there is that other voice when you are feeling crappy or something hurts- LISTEN to that voice too! I WISH I had listened to that little voice when I did my last run (6 weeks ago) But I digress..
Think about it this way, a day for 2 off will NOT affect your upcoming race or season. But training through sickness, logging 2-3 days of sub par workouts, and than falling really sick can by 10-14 days - now depending on where you are in the season and your training this can mess you up. Knowing how hard my athletes train, a day or 2 off, will not affect much. We readjust the week and go forward when you are feeling well.