Should you exercise when you have a cold or the flu?
Most doctors allow their patients to exercise when they have a cold, as long as they don’t have a fever and their muscles don’t hurt when they exercise. However, it’s probably better to stop exercising altogether when you have an infection. You risk injury if you exercise when your muscles hurt at rest or when you start to exercise. When muscles are damaged, they release enzymes from their cells into the bloodstream and they fill with blood from broken blood vessels. One study reported markedly increased muscle damage during relatively minor exercise during an infection, with blood tests demonstrating increases in muscle enzymes and ultrasound tests demonstrating hemorrhage into the muscles.
You also should not exercise when you have a high fever. When you exercise, your heart has to pump blood to your muscles to supply them with oxygen. It also has to pump blood from your muscles to your skin where the heat is dissipated. When you have a fever, your heart has to work extra hard to get rid of extra heat. Furthermore, some viruses that infect your nose and throat can also infect your heart muscle. The combination of the extra work and an infected heart muscle could cause irregular heart beats. You won’t lose much conditioning unless you take off for more than a week.