One of my Favorite Clients(They all are really!) just called me to inform me that she won't be able to make tomorrow morning's session because she feels like she got hit by a truck!!! A big one too.
So should one workout when they have the flu? No!!!! It is always better to skip a workout when your not feeling well , then it is to tough it out and risk getting worse than you already are. It's not only good to this , but also very considerate to others around you. You don't want to spread your flu to others. Especially your trainer!
Now if your symptoms are above the neck , stuffy nose(clear discharge) or a scratchy throat. Then go ahead and workout. But make it light. Real light. A light workout when feeling this way may help clear your sinuses but always make sure to drink plenty of water during your workout and after as well. If you begin your workout and things start taking a dive for the worse. Call it a day.
If your symptoms are worse than the common cold factors-such as chest congestion , fever , chills , muscle aches , etc..... Most definitely do not workout. Complete rest should be the only thing your body and mind should be exercising till you are fully recovered.
Once you feel normal , than start light again. Sure , you may have to start from a few steps back. But it won't be long till your back to where you once were.
Always remember that exercising with an infection or flu does nothing for you but put you at risk for more serious illness. Always listen to your body. It knows you better than you might think!