For most athletes getting sick raises the question of if they should work out or not. The answer isn't always simple, but the first step is to sit down and evaluate what exactly you are feeling to decide on the right course of action. Feel free to skip to the bottom if you are already feeling sick and just want to know if you should work out or not, but trying to prevent seasonal cold & flu might be your best bet.
An ounce of prevention is worth a pound of cure
Let's start by talking about prevention. Although the average adult gets two to three upper respiratory infections a year it doesn't mean you have to.
Avoid over training.
While studies suggest being active will help reduce the chances of catching and the duration of a cold, the average triathlete flirts with over training which can hinder your immune response. Over training is a major contributing factor for many triathletes and one of the best ways to measure this is with your morning heart rate. Make a habit of taking your pulse first thing in the morning before getting out of bed, make it a part of your training journal with notes about how you are feeling in a general sense. After establishing a good baseline on well days, you can assess mornings that you wake up fatigued and or sore. With a heart rate that is 5% higher than your base you will want to scale back your workout that day and lower the intensity. If your heart rate is 10% higher than the base, just take the day or two off completely to rest. Also know the other symptoms of over training