When to Work Out Through Sickness: As the seasons change I will often come down with one type of sickness or another. Whether a pesky cold, or the full blown flu, it never fails. The worst part about being sick is the interruption of our exercise program. Now, if you exercise on a regular basis you understand this. It takes weeks to get acclimated to a routine and only one week to lose all the endurance you’ve gained. It is frustrating having to lay low and heal.