How about a workout at an airport gym during long layovers?

Work out while waiting for your flight? That's an option now at Baltimore Washington International Airport, where the only gym at a US airport past security opened this week with plans to open 20 more at airports by 2020.

It's the latest example of how fitness and health trends have started showing up at airports. Yoga rooms and walking tracks have opened at airports around North America over the past few years, and healthier food options are also easier to find in airports now. You can even get a kombucha to wash down a salad made with locally sourced produce.

The ROAM Fitness gym at BWI includes an attendant who monitors guests' flights and will alert them if there's a delay. There's even free luggage storage, options for renting workout clothes and shoes, and showers. Fees range from $40 a day to $175 a month.

The concept was initially envisioned for international travelers and others with long layovers, but research revealed that many other travelers wanted to squeeze in a workout before or after landing.

"A lot of people coming from the West Coast taking red-eye flights are going straight to their business meeting but they land at 6:30 in the morning. They can't check into their hotel yet ... so it just gives them the opportunity to clean up before they head to that meeting," said ROAM Fitness CEO Cynthia Sandall.

Roughly 4,000 travelers a month use GoodLife Fitness' gym at Toronto airport, a 33 percent increase from when it opened in 2014, the company said.

But the concept may not work everywhere. The airport at Las Vegas had a gym that closed. Christopher Berger, who chairs the American College of Sports Medicine task force on healthy air travel, says the gyms' success may depend on the destination. He thinks they may be best suited for hubs with long layovers.

"You take someplace like (Chicago) O'Hare, Minneapolis, Portland, Seattle ... I think you've got a real chance of selling it," he said.

San Francisco airport's yoga room has been so successful that a second one opened in 2014. Airport officials say it's used daily. After a few downward dogs, yogis can also order a green juice or curry bowl at The Plant Cafe where everything is made with local and organic ingredients. There's also Napa Farms Market, Joe & the Juice and new vending machines offering organic, gluten-free and sugar-free snacks.

Other amenities in the pipeline as major airports look to become destinations in their own right include movie theaters, more fine dining and better shopping, says Lorraine Sileo, a senior vice president with the travel market research firm Phocuswright.

But fitness and wellness offerings may be especially appealing to travelers getting on or off cramped planes.

At Dallas-Fort Worth International Airport, there's a yoga studio with free mats, a walking path and two 55-foot staircases for an extra cardio challenge. Minneapolis-St. Paul International Airport has a 1.4 mile walking path. Philadelphia's airport had a temporary program where passengers could cycle on stationary bikes while waiting for their flights. Baltimore Washington International also offers bike rentals and a 12.5-mile trail just outside the airport.

While airports still sell plenty of greasy fast food, many airport eateries also now feature local, organic ingredients and vegan and gluten-free options. Icebox Cafe at Miami International Airport, which uses locally sourced food, reported above-average sales of $3.1 million last fiscal year. Other examples of vendors bringing healthier fare to airports include Nature's Table in Atlanta and Orlando, Elephants Delicatessen at Portland International Airport in Oregon, and French Meadow Bakery, in four airports including Minneapolis and Salt Lake City.

Ann Gentry, founder of the popular vegan eatery Real Food Daily, has an airport location in addition to two others in the Los Angeles area.

"I knew it was going to be a hit because in our (two other restaurants) people were coming in getting bags of food for the plane, so we were very accustomed to packing up food for the plane," she said.

But not everyone who patronizes Real Food Daily at the airport location realizes it's vegan. Some order a spicy lentil burger and bring it back complaining they didn't know it wouldn't have meat. On the flip side, some travelers say they enjoyed her airport grub so much they sought out the restaurant while in town.