"The purpose of warming is that it gradually increases the heart rate and circulation, which will then loosen joints and blood flow, through different ranges of motion," Koshaba says. "Stretching the muscles prepares them for physical activity and prevents injuries."
Skipping this step can increase your odds of strains and tears, ligament damage, and restrict your range of motion. "You are not performing at complete muscle and cardiovascular output," he adds.
"It's better to sweat it out when you're sick"
Working out with a cold is generally thought to be OK -- helpful, even -- assuming you feel well enough to power through a workout. "Low to moderate activity in the very early stages of a cold and/or flu can help the body fight off sickness, but high-intensity training is not advised," Koshaba says. You don't want to spread your germs around at a crowded gym, so either work out solo or wait until you're well enough to exercise.