Which Comes First, Cardio or Weights_ - Alex Hutchinson [9]
High-traffic areas are the most problematic. Australian researchers recently asked test subjects to jog back and forth alongside a four-lane highway and found elevated blood levels of volatile organic compounds, commonly found in gasoline, after just 20 minutes. But pollution levels drop exponentially as you move away from a roadway, according to a 2006 study in the journal Inhalation Toxicology. Even just 200 yards from the road, the level of combustion-related particulates is four times lower, and trees have a further protective effect—so riverside bike trails, for instance, have dramatically lower pollution levels than bike lanes along major arteries.
If you usually commute to work on foot or by bicycle, you might think that you’d be better off driving or taking the bus when pollution levels are high. But it’s not clear this is always a good choice (not to mention the fact that choosing to drive makes the pollution worse for everyone). A Danish study in 2001 measured pollution exposure while driving or biking along identical routes in Copenhagen. It turned out that the air inside the cars was bad enough that, even taking into account that cyclists were on the road longer and breathing more deeply, the drivers were worse off. On the other hand, an Irish study in 2007 found that cyclists were worse off than bus riders because of their heavy breathing, even though the air on buses was worse than the air outside.
This all sounds a bit confusing—fortunately, researchers at the University of Utrecht crunched a massive set of data to estimate the overall pros and cons of a large number of people switching from driving to biking. On average, sucking in pollution on a bike would shorten your lifespan by 0.8 to 40 days, and the increased risk of a traffic accident would knock another five to nine days off, they concluded. But the health benefits from improved physical fitness would extend lifespan by 3 to 14 months!
When you look at it that way, the trade-off seems worthwhile. But it doesn’t have to be an all-or-nothing proposition: changing your route to avoid high-traffic areas, changing your schedule to avoid the middle of the day, or simply going a little easier can all reduce the impact of bad air and still let you get a workout in.
How will exercise affect my immune system?
Although scientists aren’t sure exactly how it works, recent studies offer plenty of evidence that regular exercise really does strengthen immune function—a claim that can’t be made for most of the pills and potions whose sales spike each year when cold and flu season starts. But like any powerful medicine, exercise carries the risk of an overdose. “It’s what experts call the ‘J-curve’ hypothesis,” says Brian Timmons, a researcher at McMaster University’s Children’s Exercise and Nutrition Centre. “Moderate intensity is good, but too much exercise is not so good.”
This effect is illustrated in a 2005 study from researchers at the University of Illinois, in which three groups of mice were infected with a flu virus. One group was sedentary, another exercised for 20 to 30 minutes a day, and an extreme group exercised for 2.5 hours a day. The moderate group had an 82 percent survival rate, almost double the 43 percent rate of the mouse potato group that didn’t exercise at all—clear evidence that exercise boosted immune function. The heavy-exercise group, on the other hand, had a reduced survival rate of just 30 percent—lower than both the others. The researchers suggest that physical activity tinkers with the balance between two types of immune cell that either promote or inhibit inflammation. Moderate exercise tilts the balance to limit excess inflammation. But prolonged, intense exercise suppresses inflammation too much, preventing