You work out. Your weekly gym line-up includes running for cardio, amped up with high intensity interval training (HIIT), yoga for flexibility, and a couple of days off. "You've got this," you think, that is, until a cold or flu hits you.
Then, a dose of listening to your body coupled with common sense really should prevail. Trainers and physicians generally agree: Don't exercise if you have a fever, you're extremely tired, or achy all over.
We asked experts to offer their insights about working out while under the weather.
Tim DiFrancesco is a physical therapist, doctor of physical therapy, athletic training certified, certified strength and conditioning specialist, and the former head strength and conditioning coach for the Los Angeles Lakers and founder of TD Athletes Edge. He spoke to HealthCentral in a phone interview.
"To move or not to move is the question," he says, when you feel like: "Uh-oh, I feel a cold coming on." That may mean your nose runs, you sneeze or your throat hurts. Ugh.
Don't sweat yet
"If you're attached to a tissue box, maybe just take a walk that day," says DiFrancesco. "Stepping back is OK. You won't set yourself back in the short run, and you'll regain your overall progress when you push through the illness. There are times when life just gets in the way."
Don't plan on the most intense, heaviest workouts of your normal routine, he says.
"You want to move within comfortable and tolerable levels, mild to moderate. Do any sort of activity or movement that allows you to hold a conversation, but not necessary break a sweat."
Moving can be a good thing, especially if it's sunny and you can snag some vitamin D to bolster your immune system, he says. If you're pretty well conditioned, meaning you've done your workout consistently for years, you're probably safer exercising than someone who isn't in your fitter shoes. That's because exercise is a form of bodily stress, albeit positive stress.
If you work out inconsistently, trying to achieve a new, higher level when you're sick could add more stress — and it's not recommended.
"The goal should be to live healthy another day," says DiFrancesco.
Why we love exercise
"In general, exercise is good for you," said Ian Tong, M.D., chief medical officer of Doctor on Demand, the next-generation healthcare service providing video visits with board-certified physicians and mental health professionals. He's also Clinical Assistant Professor at Stanford University Medical School. HealthCentral reached him by phone.
A number of studies have shown that moderate exercise decreases inflammation in the body.
"The more active you are, the less C-reactive protein you make," Dr. Tong says.
"Elevated levels of this protein have been linked to increased risk of poor outcomes in patients hospitalized with heart attacks."
Other research has found that moderate exercise is associated with a 30 percent lower incidence of upper respiratory infections.
"However, if you do high levels of intensive exercise, there's some evidence that might increase risk of upper respiratory infection," says Dr. Tong.
Studies have shown that it's safe to recommend exercise for almost everyone, he says.
"Exceptions include those with certain conditions such as unstable angina, a condition in which the heart doesn't get enough blood flow and oxygen."
A rare disorder called exercise-induced anaphylaxis may cause life-threatening symptoms or hypersensitivity to skin, the respiratory or gastrointestinal tract, or cardiovascular system.
Not just about you
You're a virus carrier and when you have a cold, then sneeze, cough or touch a surface, you're spreading the illness. You can have a cold for up to 10 days, and you're contagious during that entire time, especially when you start having symptoms.
Flu symptoms can also last 10 days. The virus sheds and spreads, with the majority of shedding happening during the first two to three days after the illness begins, says a study in The Journal of Infectious Diseases.
"Don't put your hands on things like gym equipment, if you can remember," says DiFrancesco.
"Use a towel during your workout, as well as disinfecting wipes," recommends Dr. Tong. "Any part of the body with respiratory droplets on it can spread cold and flu viruses. When you touch affected equipment and rub your nose or eyes, the virus can travel from cell to cell through the entire body."
Indeed, if you have the flu, don't be around people period, he warns, and with good reason. The Centers for Disease Control and Prevention (CDC) estimates that influenza has resulted in between 9.2 million and 35.6 million illnesses, between 140,000 and 710,000 hospitalizations and between 12,000 and 56,000 deaths annually since 2010.
Easy does it
"Wait 48 hours after the fever of a cold or flu before returning to the gym, for your health and others'," says Dr. Tong. "We have bacteria on our bodies at all times, and the immune system does a good job of keeping them in check. However, cold temperatures suppress the immune system and its ability to protect us."
People with suppressed immune systems are more likely to get sick during cold and flu season. That includes people with cancer, diabetes, or HIV, he says.
On the subject of immunity, Medline Plus cites a few theories that exist around the relationship between exercise and immunity to illnesses:
Physical activity may help flush bacteria out of the lungs and airways and that may protect against a cold, flu, or other illness.
Exercise causes changes in antibodies, or white blood cells (WBCs), that fight disease. These antibodies or WBCs circulate more rapidly, so they could detect illnesses sooner. Researchers don't know if they prevent infections.
Your body temperature rises briefly during and right after exercise, and may hamper the growth of bacteria and fight infection better. This happens when you have a fever.
Exercise prevents stress hormones from being released as quickly. Stress can increase the chance of illness. Lower stress hormones may offer protection against illness.
Take care of you
Treat your whole sick body gently, and try to get to bed earlier in a sleep environment that allows you to optimize your time in bed, DiFrancesco says. That includes reducing noise and light, and monitoring temperature.
"This is an ideal time to eat healthier, with colorful fruits and vegetables, maybe prebiotics and probiotics added to your vitamin and supplement routine," he says.
In fact, a 2013 review in the Korean Journal of Family Medicine reported that probiotics may have a modest effect in common cold reduction. An earlier study in Pediatrics found probiotic supplementation could reduce cold and flu-like symptoms in children by 50 percent.
Your illness will be short. You've got a lifetime to work out smarter and stronger once you're well.