For the physically active, outdoor exercise in Atlanta during the summer presents a conundrum: When the smog is high, do you recreate or hibernate?

That question vexes runners and cyclists, among others, who can't help but wonder if they're doing more harm than good when they exert on particularly polluted days.

The specter of more smog alerts arose when the Environmental Protection Agency last week imposed stricter limits on ozone. Last summer there were 29 days in metro Atlanta that merited a smog alert; now there could be one every other day.

On the worst days, people, especially children and those with respiratory woes, are urged to stay inside. Sporty types who stand to suck in all that awful air seem bent but unbroken by the news.

"It's like smoking: Today it felt great," said cyclist Mike Harris, drawing an interesting analogy.

Harris, who often bikes the 29 miles to his job in Ansley Park from Marietta, added, "The smog is worse in the heat of the day and the evening. Hopefully, I'm getting enough good from the morning ride to offset the bad at night."

Greg Masterson, president of the Metro Atlanta Cycling Club, said he's "aware" of smog alert days, "but I go ride anyway, and I will continue to do that."

In the summer, Masterson said, he rides 150 to 200 miles a week, mostly at night.

Masterson said poor air quality, "makes you want to drive to Dahlonega." Still, he's comfortable riding even on smog alert days.

"Some people have asthma," he noted. "I don't."

Steven Nagata said he's "not as sensitive to smog as maybe some people are." But the Roswell running store owner said he sometimes adjusts his training schedule according to the conditions.

"Obviously, as runners, our biggest concern is respiratory," said Nagata, "so, to some extent we alter the time of day or the days of the week that we run."

That might mean running in the morning instead of the early evening, or pushing a session back a day.

As much a factor as the smog, he said, is the Georgia heat and humidity. The heat index is as likely to keep runners home as pollution.

Harris said the level of concern over smog alerts varies widely.

"The informed are going to pay attention," he said. "Ignorance is bliss, particularly if you're 30 years old and don't have asthma. But the more informed you are, the more frightened you become.

"Should it matter? Probably."