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A Utah transplant who came to the state to run competitively for the University of Utah, BJ Christenson still remembers the first time he ran in inversion-induced pollution.

"I just remember feeling like it was coating my teeth," he said. "But we ran through it."

"Just run through it" is a way of life for most hard-core runners, said Christenson, now a manager at Salt Lake Running Company. But lately, he said, local runners and other athletes have begun to voice concerns about the effect that polluted air might have on their health.

And they might be on to something, according to Robert Paine, a pulmonary physician at University of Utah Hospital.

When people exercise, Paine said, they breathe faster to bring more air into their bodies. Anything in the air small enough to bypass the respiratory system's natural defenses also comes in with each breath, so those who exercise outdoors when the air quality is poor get a much bigger dose of pollutants — making 3 miles feel like 6, lengthening recovery time and increasing one's risk of having a heart attack that day. And exercising repeatedly in bad air could possibly lead an athlete to develop asthma.

So if pushing oneself to run during an inversion won't build endurance — and might actually do the opposite — is it better to skip the workout when air quality is bad?

On the Wasatch Front, levels of particulate pollution — PM 2.5 — are low throughout most of the year, but spike on certain days — so the issue is acute (short-term) exposure, not chronic exposure. If an athlete is exposed to high concentrations of PM 2.5 once, their body will repair that damage within a few days and life will continue as usual.

But Kenneth Rundell, a retired research professor who dedicated his career to studying air pollution and athletic performance, said that if another exposure — and then another, and another — occurs before the body has a chance to repair itself, the incomplete repairs build upon each other, eventually becoming chronic inflammatory conditions.

PM 2.5 refers not to a particular chemical or gas, but to a whole class of airborne particles characterized as similar because of their size — ranging from 25 to 100 times thinner than a human hair. This fine particulate matter is considered more harmful than PM 10, the classification for larger particles, because smaller particles can travel deeper into the lungs.

Researchers haven't pinned down the frequency at which acute exposures to PM 2.5 become a chronic issue, but Rundell estimated that regular exposures would have to occur in the range of five days per week for a considerable length of time. Last January, downtown Salt Lake City exceeded the Environmental Protection Agency's health standard for PM 2.5 on four days; in January 2014, it exceeded the standard on 13 days.

And it is clear, Rundell said, that chronic exposure to PM 2.5 does cause permanent damage to the lungs.

When we inhale PM 2.5, Paine said, the particles get deposited inside the lungs, causing irritation, inflammation, and decreased lung function that can last for 24 hours. That's especially problematic for people with chronic respiratory conditions like asthma, whose symptoms can be easily triggered by particulate pollution.

Healthy individuals' bodies will also respond to particulates, but the inflammation and decreased lung function won't be as severe, so they may not notice, said Rundell, who was an adviser to the United States Olympic Committee during the 2008 Olympics in Beijing and is now an independent lecturer based in Pennsylvania.

Rundell said research has found elevated rates of asthma among skiers and among Californian children who played outside more than once per day.

The skiers, he said, likely developed asthma because of their habit of practicing for very long periods of time, which prevented their respiratory systems from self-repairing. The children were probably student-athletes who played more than one sport, causing them to exercise in a polluted urban environment more frequently.

Even athletes who practice indoors aren't immune to air pollution. He said his research has also demonstrated that figure skaters, swimmers, and hockey players are at risk because chemicals in the ice and in the water form PM 2.5, which builds up in inadequately ventilated indoor spaces. Over time, chronic exposure to these polluted environments causes predisposed individuals who frequent them to develop asthma.

In one of Rundell's studies, almost half of the children who came to a figure skating clinic tested positive for asthma.

A question yet to be answered is whether the damage sustained during just one acute exposure to pollution could have long-term, life-altering effects like asthma or even cancer.

Rundell's inclination is to say no. But Paine points out that people picking up an exercise routine for the first time, or for the first time in many years, face a less dire but possibly more certain long-term consequence of running outdoors during an inversion.

If the air they're breathing is polluted, those first workouts are going to feel more difficult than they would otherwise, Paine said. And if working out feels too hard, people are less likely to stick with it, he said, robbing themselves of the long-term benefits of an otherwise healthy lifestyle change.

"Those new shoes would do very well on a treadmill" during an inversion, Paine said.

Damage caused by particulate pollution goes beyond the respiratory system. It's possible for these tiny particles to enter the bloodstream and travel to other parts of the body, including the heart and brain.

Rundell conducted research that demonstrated that the cardiovascular system does not function properly in the presence of small particle pollution — and the smaller the particles, the more severe the impact.

During exercise, a person's vessels dilate and their heart pumps faster to serve more oxygen to their muscles. But exposure to particulate pollution lessens the ability of blood vessels and arteries to dilate, making the cardiovascular system less able to adapt to stress.

In susceptible persons, Rundell said, this can cause a heart attack.

Though individual risk varies, Paine said, the general rule is that an individual's odds of having a heart attack on any given day increases by 4 percent for every 10 micrograms of PM 2.5 per cubic meter of air that a person is exposed to on that day. The EPA has set the health standard for short-term exposure to PM 2.5 at 35 micrograms/cubic meter; the Air Quality Index will report an "orange" air quality day at this level of concentration. Based on Paine's rule, the risk of having a heart attack on an orange air quality day is increased by about 14 percent.

Whether that increased risk is a real concern for a given individual depends largely on that person's standing heart attack risk — the Mayo Clinic provides a quick estimate at For a healthy 20-year-old with a low probability of having a heart attack, 14 percent may not be much of an increase. But for someone who is in general much more likely to have a heart attack on any given day — due to age, weight or family history — 14 percent might be a big problem.

Heart attack isn't the only risk that comes with acute exposure to PM 2.5, Paine said. High concentrations of PM 2.5 have also been associated with an increased likelihood of stroke, and, for pregnant women, pre-term birth.

Given all those combined risks, Paine said, he tends to advise all people to avoid exercising when the air quality is deemed unhealthy in their area.

"My conservative approach," he said, "is that even if you're healthy, that's a kind of stress that is to be avoided if possible."

Whether to run on a marginal or yellow day is a trickier question.

It all comes down to how sensitive you are to particulate pollution, Paine said. For some people, such as those with chronic conditions like asthma or chronic obstructive pulmonary disease, the sensitivity is obvious. But even those who don't have an obvious health risk can be sensitive, Paine said.

The telltale sign, he said, is whether vigorous activity on a yellow or orange day leaves you wheezing. In the winter, this could be confused with another common running malady called lung burn — a burning sensation in the chest and throat that some runners get on cold days when the cells lining the upper respiratory system become dehydrated by the dry air.

But lung burn should not restrict your breathing, Paine said. Runners who experience coughing, wheezing or a tightness in their chest that lingers after a run may actually be sensitive to particulate pollution.

Rundell also emphasized the importance of personal sensitivity. The majority of the population never develops chronic symptoms, even in the riskiest environments, Rundell said, and those who do develop asthma probably had a predisposition for it.

Both agreed that people new to exercise should talk to a doctor to determine whether they have underlying risks that could make it unsafe to work out when the air is bad.

"Those people need to listen to their doctor," Rundell said. He also cautioned against exposing children to air pollution during physical activity because, he said, children are more susceptible to respiratory damage and therefore to developing asthma down the road.

Rundell said that if he were a runner or cyclist in Utah, he'd hit the trail during inversions. Concentrations of particulates are highest near the source, so he would avoid busy roads and take his workout someplace a little less urban.

Runners can also seek refuge in the same mountains that contribute to the valley's pollution-trapping inversions. Heading to 6,000 feet or higher will bring you above the harmful smog, Paine said.

Wearing a mask could help with avoiding pollution, but not all masks are able to filter out PM 2.5, and those that are might not be comfortable to wear while exercising, Paine said.

Christenson said he now regularly discusses those options with his customers during inversion season. If someone is determined enough, he said, it's entirely possible to avoid the bad air and remain physically active. He carries filtration devices, he said, and he often points runners to the indoor track at the Olympic Oval or to local canyons.

If there's no other option, Christenson said he believes running outdoors in polluted air is still better than sitting inside watching TV. But he doesn't advocate making it a regular habit — rather, he said, runners should pay attention to how they're feeling while they run.

"I'm always one to listen to my body," he said. "If my body says no, I don't do it."

Twitter: @EmaPen —

What running on a red-air day does to the body

Lungs: Harmful particles are deposited deep inside the lungs, triggering inflammation and irritation, and resulting in decreased lung capacity that may persist for 24 hours.

*Those with asthma, chronic obstructive pulmonary disease or a similar condition will experience worse symptoms.

Vascular system: Particles deposited in the lungs may be absorbed into the blood stream, allowing them to move throughout the body. Blood vessels are less able to dilate, restricting blood flow and suppressing the body's natural response to stress.

Heart: Particulates in the bloodstream make their way to the heart, and for the next few days after the exposure, the individual has an increased probability of having a heart attack.

Brain: Some studies suggest there is a correlation between particulate exposure and stroke, but the exact relationship is unclear.

Muscles: Even in highly trained athletes, peak exercise capacity is decreased. One trial found hockey players' capacity for exercise decreased by about 5 percent after being exposed to particulates in an artificial environment.

Womb (for women): A study from Utah County suggests that pregnant women who were exposed to PM 2.5 were more likely to enter labor prematurely. Is that lung burn or pollution in your lungs?

Lung burn:

Caused by: cold, dry winter air dehydrating tissues in the upper respiratory system

Symptoms: painful, burning sensation in your throat and chest

Solutions: proper hydration, focus on taking long, deep breaths instead of quick, short breaths


Caused by: Tiny particles becoming lodged deep within the lungs, triggering inflammation

Symptoms: coughing, extreme shortness of breath, tightness in the chest, wheezing

Solution: exercise indoors, recreate above 6,000 feet in elevation, or wear a properly fitting mask What level of exposure is safe?

Yellow/orange air quality: Sensitive populations, including those with respiratory or cardiovascular conditions, the children and the elderly, should limit outdoor activity.

Red air quality: Outdoor cardiovascular exercise is not advised for all populations. Casual exposure (such as walking down the street) is OK for healthy individuals.