Cold or Fever: Should You Exercise?

Exercise may actually be beneficial when you have a cold. However, it's probably better to stop exercising altogether if you have a fever with aching muscles. When you exercise, your heart has to pump blood to your muscles to supply them with oxygen. It also must pump blood from your muscles to your skin where the heat is dissipated. When you have a fever, your heart has to work harder to get rid of extra heat.

You risk injury if you exercise when your muscles hurt at rest. 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 showing increases in muscle enzymes and ultrasound tests demonstrating hemorrhage into the muscles. You will not lose much conditioning if you take off a few days.

How Exercise Preserves Brain Function

Dr. Yu-Min Kuo, of the National Cheng Kung University Medical College in Taiwan, has shown how exercise helps to preserve brain function as you age (The Journal of Applied Physiology, November 2008). Dr Kuo trained mice to run daily for five weeks on wheels at 70 percent of their capacity. They started to exercise at 8, 12 and 24 months of age. These ages are equivalent in humans to ages of 40, 60 and 90 years.

The mice that exercised every day grew 2.5 times more new brain cells than those who did not exercise, and these new nerves helped them to learn and memorize new tasks. The increase in brain cells came from increased production of signaling molecules that promote brain cell growth.

However, the mice that started exercise in early middle age (equivalent to age 40) did much better than mice that did not start exercising until later middle age (equivalent to age 60). This would indicate that the capacity of exercise to help you maintain intelligence decreases after middle age.

When you are young, your body continuously creates new brain cells. As you age, your brain loses its ability to regenerate new nerve cells. This is why you gradually lose some of your ability to remember and learn. We don’t know if Dr. Kuo’s results would be found in humans, but his study should encourage people to start exercising while young and continue throughout their lives.