Should you exercise when you're sick?

The winter cold and flu season may try to knock out your new year's plans to get or stay healthy, but the good news is you can fight back.

Dr. Jayson Loeffert, a sports medicine physician at Penn State Health, said it's typically okay to continue your regular exercise routine when you have a cold.

Exercising when sick increases your heart rate, gets your heart pumping and promotes healthy blood flow. It also opens up your lungs and releases endorphins. All of that can help you feel better.

If you feel tired sooner than you normally do, it's also okay to scale things back to what you can tolerate.

"If you are really congested or wheezing, you might be short of breath, so you'll want to decrease the intensity," he said. Severe fatigue or uncontrolled coughing are signs that it's time for rest.

Two environments can cause trouble for exercising when you're not feeling well.

Loeffert said some people have trouble breathing when exercising outdoors in the cold, dry air and may want to move their workout indoors until they feel better.

Swimmers who are congested may have more difficulty with their breathing, and the chlorine in a pool can make the congestion worse.

He said those who have gastrointestinal trouble may find running or other activities problematic or uncomfortable and want to skip them until they feel better.

Loeffert does not recommend beginning an exercise routine when sick because you don't have a baseline to which you can compare your body's response.

The one time he always advises against exercising is if you have a fever.

"Exercise naturally causes an increase in body temperature. When you have a fever, your temperature is already higher than normal. If you have a fever, exercise can then cause your body temperature to be further increased to an unsafe level," he said.

For people who exercise in a gym or other shared space—or who share equipment—he reminds them to always cover their mouth with their arm when they cough so they aren't spraying germs into their hands.

He also recommends wiping down any equipment with sanitizing gel or wipes when you finish using it and added: "I have also seen people wearing masks in group exercise classes to be considerate."