Too much exercise can weaken rather than strengthen the body, experts say.
Henry Ford, the Model-T tycoon who put America on wheels and thus shares some of the blame for the fact that far too many of us are lazy and fat, took a dim view of the pursuit of fitness.
“Exercise is bunk,” he once declared. “If you are healthy, you don’t need it. If you are sick, you shouldn’t take it.”
Ford was a manufacturing genius, not an exercise physiologist. Nevertheless, in this season of colds and the flu, his words are worth pondering. When it comes to fending off viruses and infections, the scoop on exercise is this: While some may be better than none, too much can be worse than none.
The U.S. Centers for Disease Control and Prevention estimate that each year Americans are afflicted by more than 425 million colds and flus.
Ken Cooper is the guy who coined the term “aerobics” and can be rightly regarded as one of the fathers of the Fitness Revolution. His current creed: Excessive exercise actually can be toxic.
Overtraining can overwhelm the immune system with free radicals, he asserts. These noxious renegades make the body not only more vulnerable to run-of-the-mill viruses and infections but also major-league killers such as heart disease and cancer.
Over the years, he has been struck by how many elite athletes have been visited prematurely by such life-threatening scourges: cyclist Lance Armstrong, skater Scott Hamilton and runners Marty Liquori, Steve Scott and Mark Conover.
“Excessive exercise can backfire on you,” says Cooper, a physician who heads the Cooper Institute for Aerobic Research in Dallas. “There appears to be a point of diminishing returns where your immunity is adversely affected and you break down your resistance to infection and disease.”
Where that point is, of course, is the $64,000 question. “How much is too much?” asks Cooper. “It varies according to the fitness level of the individual. What might be too much for me is not too much for Frank Shorter.”
Nevertheless, a growing body of evidence–some anecdotal, some gathered in the lab–suggests that heavy exertion and overtraining can impair immune function, thus increasing the risk of illness. In one study, more than 2,300 runners who participated in the 1987 Los Angeles Marathon were surveyed. During the week after the race, one out of seven got sick, a rate nearly six times that of runners who trained but did not run the marathon.
Moreover, during the two-month period before the event, runners who trained more than 60 miles a week doubled their odds for illness compared with those who logged less than 20 miles a week.
Uta Pippig, winner of the 1994 Boston Marathon, caught a cold the week before the race after running 140 miles a week for 10 weeks at high altitude. While training for the 1984 Olympic Marathon, Alberto Salazar was hit by 12 colds in 12 months. “My immune system was totally shot,” he recalled. “I caught everything. I felt like I should have been living in a bubble.”
The immune systems of marathoners have been studied in the lab before running and after running for two to three hours. After such exertion, immune function dropped sharply, reports David Nieman, a professor of health and exercise science at Appalachian State University in his book, “The Exercise-Health Connection” (Human Kinetics, $14.95).
The apparent reason? Extreme exercise releases a flood of stress hormones, which allow germs and other nasties to gain a foothold during an “open window” of vulnerability that can last from 3 to 72 hours.
Heavy training day-in and day-out also has been linked to a chronic suppression of neutrophil function. This is a critical finding, says Nieman, because the white blood cells called neutrophils are an important part of the immune system’s “first line of defense.”
That’s the bad news. The good news? “Moderate” exercise seems to strengthen the body’s resistance. In surveys, runners and master athletes report fewer colds and sick days than their sedentary peers. And studies show that people who engage in daily walks of 40 to 45 minutes at a crisp pace cut colds and sore throats by half.
During moderate exercise, several positive changes occur in the immune system, says the American College of Sports Medicine. Various immune cells circulate through the body more rapidly and are better able to kill invading bacteria and viruses. Furthermore, stress hormones, which can suppress immunity, remain unelevated. Although the immune system returns to pre-exercise levels within hours after the workout, each session represents a boost that appears to reduce the risk of infection over the long term.
“When moderate exercise is repeated on a near-daily basis,” says Nieman, “there is a cumulative effect that results in an improvement in protection of the exerciser.”
Nieman likens it to “having a housekeeper come to the house every day for 35 to 45 minutes to tidy things up. By the end of the month, the house will be relatively clean and organized. In other words, every time an individual goes for a walk, the immune system receives a boost that should increase his or her chances of fighting off cold viruses over the long term.”
Steve Gluckman, an infectious disease authority at the Hospital of the University of Pennsylvania, is not convinced that the link between heavy-duty exercise and susceptibility to illness has been proved. But he is sure that some exercise will not only do you no harm but probably plenty of good.
Lab studies show, he says, that “many aspects of the immune system are improved even after modest amounts of aerobic exercise.” Exercise gets the body moving, the glands and organs pumping, the blood flowing. It stirs white blood cells and rallies other disease-fighters such as immunoglobulin. It also releases adrenaline and natural steroids and opiates, all of which ease discomfort and mitigate the symptoms of sickness.
