The answer is always NO if what you have is contagious! While it’s generally ok to exercise with a mild illness, keep in mind that you might spread germs to others and cause them to become ill.
Below is some good advice from our friends at WebMd if you are thinking about hitting the gym when you are under the weather.
You have been so great about your new exercise routine, rarely missing a day since you started up again. Then all of a sudden you are waylaid by a cold or flu.
What should you do? Should you skip the treadmill or forsake that Zumba class for a late afternoon nap? Will it be hard to get started again if you skip a day or two? The answer depends on what ails you, experts tell WebMD. For example, exercising with a cold may be OK, but if you've got a fever, hitting the gym is a definite no-no. Fever is the limiting factor, says Lewis G. Maharam, MD, a New York City-based sports medicine expert. "The danger is exercising and raising your body temperature internally if you already have a fever, because that can make you even sicker," he tells WebMD.
Maharam's rule of thumb for exercising when sick? "Do what you can do, and if you can't do it, then don't," he says. "Most people who are fit tend to feel worse if they stop their exercise, but if you have got a bad case of the flu and can't lift your head off the pillow, then chances are you won't want to go run around the block."
Personal trainer and exercise physiotherapist Geralyn Coopersmith, senior manager of the Equinox Fitness Training Institute in New York, has this to add: "The general rule is that if it is just a little sniffle and you take some medications and don't feel so sick, it's OK to work out. But if you have any bronchial tightness, it's not advisable to be working out."
You really need to know your limits, she says. "If you are feeling kind of bad, you may want to consider a walk instead of a run. Take the intensity down or do a regenerative activity like yoga because if you don't feel great, it may not be the best day to do your sprints," says Coopersmith, the author of Fit and Female: The Perfect Fitness and Nutrition Game Plan for Your Unique Body Type.
"A neck check is a way to determine your level of activity during a respiratory illness," adds Neil Schachter, MD, medical director of respiratory care at Mount Sinai Medical Center in New York. "If your symptoms are above the neck, including a sore throat, nasal congestion, sneezing, and tearing eyes, then it's OK to exercise," he says. "If your symptoms are below the neck, such as coughing, body aches, fever, and fatigue, then it's time to hang up the running shoes until these symptoms subside."