NEW YORK (CBSNewYork) — Children with asthma have a tough time staying active and in shape, because exercise can sometimes trigger an attack.

But, as CBS2’s Dr. Max Gomez reports, there is one activity kids can do that’s both safe and can also improve their symptoms.

Kristian Jackson, 11, suffers with severe asthma, so exercise hasn’t always been easy. In fact, at times it’s even led to serious attacks.

“When it starts to flare up, like my shoulders go up. It feels tight like everything’s kind of blacking out, because it feels like I’m going to faint or something,” he says.

Kristian relies on daily medication to control his asthma and in the past, he struggled to find ways to safely stay active. Until he was introduced to the pool.

“If you want a specific recommendation as to an activity that won’t trigger an asthma attack, swimming tends to be a great one,” Dr. Tod Olin, of National Jewish Health, says.

But for Kristian, swimming isn’t just a pastime, it’s part of his school curriculum. He goes to Morgridge Academy on the campus of National Jewish Health in Denver.

“When you get them into the pool with that warm air and teach them how to regulate their breathing, they can do a lot more with physical activity than they would be able to do otherwise,” Jennifer McCullough, with the academy, says.

The key is the humid air in the indoor pool, which keeps airways open. It’s something for all parents to consider if they have children with asthma, because excising outdoors, especially in the cold, can cause problems.

“The airways dry out a little bit, and then that sets off a cascade of reactions that ultimately squeezes down the airway,” Olin says. “So if we can prevent that initial airway-drying step by staying in a humid environment, we prevent the asthma attack all together.”

Kristian’s time in the pool has led to vast improvements in his lungs.

“It feels like it strengthens them. It really strengthens my muscles, and it’s also really fun,” he said.

Swimming helps kids control their breathing, because they’re forced to take long, deep breaths before going under water. Swimming also helps kids with asthma strengthen their lung function, so they can eventually transition into playing other sports, Gomez reports.