It seems as if everyone I meet has been the victim of some nasty virus this winter. Colds, the flu, sinus infections - you name it, someone's had it.
But when you feel a bit better, you like to get back to your exercise routines right away - after all, you've wasted enough time lying in bed, right? But how much should you do? Should you push yourself to your pre-sick activity level, or take it really easy for a couple of weeks?
First, determine if you are still a bit sick. There's that grey area when you definitely feel a lot better that you did, but you tire easily, you're still hacking and coughing, still running a bit of a fever. This is not the time start working out again. Sure, go for a walk, do stretches, even a bit of core work, but don't drive yourself to grey-faced exhaustion and into a relapse! Your immune system is already busy healing you - don't task it with intense workouts. Take it easy until you are really totally healthy.
At that point, you will have lost some of your exercise capacity - up to 30% or so. The strategy here is to start at about 2/3 of your exercise intensity and volume. In other words, work out regularly, but dial it down. The most important thing to do is listen to your body, not your buddy! S/he might want to score a new personal best this week, but your job is to stop when you have reached your limit.
Gradually increase your intensity and volume of exercise, monitoring your body's message to you, keep up good nutrition and hydration, and get 8 hours of good sleep each night. That's the best prescription for regaining your fitness after an illness.