If you're sick

If you're feeling under the weather, don't hesitate to skip your workout for some extra sleep and rest.

"Exercise is incredibly taxing on your body, so if you're feeling under the weather, an intense workout will often make you feel worse," Fried said. He noted, however, that light exercise is probably OK if you have the sniffles or a minor cold.

Fried added that if you are feeling feverish, lethargic, or sick to your stomach, you should stay home and recover.

"The gym isn't going anywhere, and your fellow gym-goers will appreciate you leaving your germs at home instead of all over the squat rack," she said.

[Photo via Getty]

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