Exercise in the Time of Flu
This fall I am particularly keen on exercise. My 15-daughter joined the track team, and in a few short weeks I can see the transformation—in her energy, in her strength, and in her carriage. As for me, exercise has not only eased an irksome hip, but it also has helped keep me sane. Awake before dawn and can’t get back to sleep? Go to a 6:15 Bikram yoga class.
But last week a post in The New York Times’ Well blog gave me pause. It reported on two recent experiments that measured how different exercise levels affected mice’s resistance to the flu virus. The blog said “the bulk of the new research, including the mouse studies mentioned, reinforce a theory that physiologists advanced some years ago, about what they call ‘a J-shaped curve’ involving exercise and immunity.” It quoted Mary P. Miles, an associate professor of exercise sciences at Montana State University, as saying that in this model, the risk both of catching a cold or the flu and of having a particularly severe form of the infection “drop if you exercise moderately.” But the risk both of catching an illness and of becoming especially sick when you do “jumps right back up,” she says, if you exercise intensely or for a prolonged period, surpassing the risks even among the sedentary.
And what constitutes intense exercise? Inquiring moms and dads with kids in school sports want to know, especially in this season of swine flu. Most researchers “define it as a workout or race of an hour or more during which your heart rate and respiration soar and you feel as though you’re working hard,” the post said.
That seems to cover a broad range of activities and levels of exertion—from preparing for a marathon to sweating 1 ½ hours in a room heated to 105 F doing a regimen of 26 postures (in other words, a Bikram yoga class). As I forwarded the blog to a friend who plans to run the New York Marathon in two weeks, I wondered whether my daughter—who runs more than an hour after school most days—and I are also in danger of sabotaging our immune systems with too much exercise.
When I posed the question to Professor Miles, she said most studies have focused on adults. Not much research has been done on adolescent athletes—or on Bikram yoga practitioners, for that matter—and she’s not comfortable extrapolating. “The one thing that I would say is that if a person seems to be getting sick frequently, then exercise volume might be a factor to consider,” she said. That’s one way to tell whether just doing it can be doing too much.