Plenty of things can play havoc on your exercise regimen this time of year. Cold weather, shorter daylight hours and holidays can all affect your training. And this is also the cold and flu season. So what happens when you come down with a cold? Should you exercise while you're sick or rest until the cold passes?

     Thanks to a recent study by Ball State University, this decision is now a little easier. It confirms a rule of thumb we've been following for a while: the "neck check."

     Simply put, if your symptoms are above the neck--runny nose, sneezing and scratchy throat--you're OK to exercise, but keep it at a moderate intensity. If you have below-the-neck symptoms--chills, fever of 100 degrees or higher, diarrhea, hacking cough, muscle aches or vomiting--take time off to let your body recover. Exercising with below-the-neck symptoms will only weaken your immune system and possibly raise your body temperature even higher.

     In the Ball State study 50 healthy students were given an upper-respiratory virus. Half were instructed to be as sedentary as possible, while the other half exercised at a moderate pace for 40 minutes a day. After 10 days, no differences were found between the groups. The conclusion: while exercise didn't speed recovery, it didn't slow it down either.

     Though exercising with a head cold can be safe, the decision ultimately comes down to how you feel. If you're up for it and have the strength, then maintain your exercise routine, but decrease the duration by half and keep the intensity at a moderate level. It's also a good idea to stick with indoor activities. If you do need to cut your workout short, the locker room is right around the corner. Plus, the intensity and duration are much easier to manage indoors.

     On the other hand, if you're weak, lethargic and just feel awful, taking a day or two off is the best medicine.