Most doctors think it is OK to exercise when you have a cold, as long as you don't have a fever and your muscles don't hurt. However, it may be better to stop exercising altogether. A recent study from Munich reported severe muscle injury from relatively minor exercise during an infection. When muscles are damaged, they release enzymes from their cells into the bloodstream and they fill with blood from broken blood vessels. This study reported that blood tests showed increases in muscle enzymes and that ultrasound tests demonstrated hemorrhaging into the muscles.
You also should not exercise when you have a 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 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 can cause irregular heartbeats.
To be on the safe side, it's better not to exercise when you have an infection or a fever.
Q: Is it a good idea to eat a candy bar just before working out? -- J.L., Duluth, Minn.
A: Scientists used to recommend avoiding sugar prior to exercise or competition because they thought that it would make you tired. But recent research shows that it can actually increase your endurance.
The old theory was that when you take in sugary food, the sugar caused your blood sugar levels to rise. When your blood sugar level got high enough, your pancreas would release insulin, and that would cause a rapid drop in blood sugar levels, making you feel tired.
The latest research shows that eating sugar before exercising does indeed cause your blood sugar level to rise and then fall, but that the drop in blood sugar level does not affect your performance. The most fit individuals can tolerate the lowest blood sugar levels. As long as you have a lot of sugar inside your muscles, a low blood sugar will not prevent you from exercising.
Furthermore, the extra calories taken before exercise can help you to have greater endurance. You feel tired when your muscles run out of their stored sugar. Taking extra food just before you exercise supplies extra calories to be burned in place of your stored muscle sugar, and that can help you to exercise longer.
Q: What's the story on growth hormones and testosterone patches for older men? -- E.W., Knoxville, Tenn.
Two years ago, a study from the University of Wisconsin was widely reported to show that growth hormones make older men more muscular, less fat and more sexual. The bad news is the results aren't that impressive, and unfortunately, taking growth hormone injections is associated with side effects such as arthritis, fluid retention and carpal tunnel syndrome.
Testosterone patches are much more promising, and they have been approved by the Food and Drug Administration. When testosterone is taken by mouth it goes to the liver, which can increase your chances of developing a heart attack by lowering the good HDL cholesterol and raising the bad LDL cholesterol. When it is absorbed by patch, it passes through the skin into the bloodstream and does not go to the liver. It raises blood levels of the good HDL cholesterol, lowers the bad LDL cholesterol, increases a man's sexuality and muscularity and lowers his body fat. A major question is whether they also increase chances of having prostate cancer spread.
Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.