Exercise Can Either Strengthen or Weaken You

Having been told by health authorities that prevention and a strong immune system are the best defense we have against SARS, people are taking to heart the advice to exercise regularly, get enough sleep, and eat healthy food.

A friend who was not eating fruits before because she was following the Atkins Diet said she's now eating two servings a day because she's scared of SARS.

Another friend whom I have been trying to convince to exercise sent me a text saying, "You win! I am now starting my anti-SARS workout." If this is the effect that fear of SARS has on people, then something good may come out of this bad situation the world is currently in.

How Exercise May Strengthen Immune System
While the field of exercise immunology is still young, researchers like David Neiman are finding evidence that moderate exercise strengthens the immune system.

In one of his experiments, Neiman found that overweight, sedentary women who walked briskly for 45 minutes five times a week had a 50 percent reduction in the duration of respiratory symptoms compared to those who remained sedentary. In other words, when they would have colds, the fitter women recovered faster.

In a study by Charles Matthews of the University of South Carolina, people who engaged in regular physical activity that included exercise, sports and chores like heavy gardening or scrubbing floors, had 25 percent fewer colds than people who were less active.

This does not conclusively prove that being physically active prevents colds, but Matthews says, "The most likely explanation for the finding is that higher levels of activity for the average person derive some benefits to their immune defenses against a cold."

At this point, scientists are still not sure exactly how exercise can enhance the immune system response. One theory is that since exercise increases circulation, immune system cells get around the body faster.

Neiman and other scientists have found an increase in various types of immune cells like natural killer cells after an exercise session. The boost lasts for a couple of hours.

Second, all the hard breathing you do during exercise rids lungs of different types of airborne viruses and bacteria. Third, the increase in body temperature can inhibit the growth of certain bacteria, making your body more effective at fighting off impending infections.

The last theory is that exercise makes your immune response stronger by relieving stress and anxiety. Stress is known to have a negative effect on the immune system.

Scientists at Arizona State University found alpha brain waves in exercisers during and after a 30-minute run similar to people in a meditative and relaxed state. So if yoga or tai chi doesn't interest you, don't worry. These esoteric forms of exercise are not the only ones that can relieve stress.

But exercise is a double-edged sword. Moderate to vigorous exercise may help you catch fewer colds and flu but extreme exercise may do the exact opposite.

Several studies have shown that prolonged endurance exercise like marathon running and long distance cycling can temporarily suppress the immune system and increase the risk of viral and bacterial infections, specifically upper respiratory tract infections.

Neiman believes this may be caused by an increase in stress hormones like cortisol that are released during and after a bout of heavy exertion.

Neiman calls the three to 72 hours of decreased immunity following prolonged heavy exercise "an open window" of vulnerability. His studies reveal that immune cells concentrate on repairing muscle damage during this period, leaving the rest of the body temporarily vulnerable to attack.

Neiman studied runners of the 1987 Los Angeles Marathon and found that those who completed the race were six times more likely to come down with a cold compared to those who dropped out of the race.

In a 1989 study of the same marathon, 13 percent of the runners came down with the flu two weeks after the event but only 2 percent of those who trained for the marathon but did not run in the race became sick. It seems that prolonged exhaustive exercise has the most negative effect on the immune system.

Neiman himself gave up running marathons (he has completed 58 marathons) because his own research convinced him it was not a healthy thing to do. Five to 21-km "fun runs" are not a problem for the immune system, according to research. It's the longer events like 32- and 56-km that can raise the risk for participants.

The terms "moderate exercise" and "extreme" can mean different things to different people. An hour of exercise a day may be moderate to a group exercise (aerobics) instructor used to teaching two to three classes daily while it may seem extreme to a couch potato who runs out of breath after climbing two flights of stairs.

While there are no hard and fast rules, Neiman says that 30-90 minutes a day of aerobic exercise is considered moderate.

For the average exerciser, Neiman recommends limiting aerobic exercise sessions to not more than 90 minutes per session because he discovered that after a three-hour run, cortisol levels stay high the whole day.

A lot has to do also with other factors like sleep, diet and psychological stress levels. It's possible for people to exercise for more than 90 minutes on a regular basis and not experience any health problems, while an hour a day may be too much for someone who is on a crash diet, smokes, and is not getting enough sleep.

Symptoms of Too much Exercise
The classic symptoms of "overtraining" or too much exercise are both physical and psychological. Physical symptoms include chronic fatigue, persistent muscle soreness, loss of appetite, unexplained weight loss, headaches, a feeling of "heavy legs," insomnia, gastrointestinal disturbances, menstrual irregularities, and frequent colds and flu.

Psychological symptoms are depression, mood changes, apathy, lethargy, low motivation, lack of concentration, anxiety, irritability/excitability, boredom, inability to relax, and anger/aggressiveness.

If you exercise a few hours a day but you don't have any of these symptoms and you are eating well and getting enough sleep, then you don't need to worry that you are getting too much exercise.

Next week: Immune system protection tips for athletes and heavy exercisers.

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