The latest fad for escaping the summer doldrums at ski resorts is not for the timid.

It involves racing down steep grassy slopes on something that looks like a long skateboard — or a short snowboard — equipped with shock absorbers and overgrown wheels jutting from the sides. “Mountainboarding” is the new thing for thrill-seeking extreme sports enthusiasts.

“It’s sort of the monster truck of skateboarding,” said Ryan Triffit, spokesman for the Sunday River ski resort in Newry. “People are lined up to try it out, and I think part of it is just because it’s so unique.”

For resorts, it is the latest way to try to make some money in the summer when the ski lifts are typically idle. Resorts like Sunday River have been letting mountain bikers use their lifts for years.

“A lot of people are looking to do more than just sit on the beach all summer,” said Stacy Gardner, spokeswoman for the National Ski Area Association.

The trend took shape seven years ago when a pair of snowboarding enthusiasts from San Francisco began looking for a board that people could use on the mountains during the warmer months.

“We thought somebody else was making it. It seemed so obvious,” said Patrick McConnell.

Nobody was, so McConnell and Jason Lee began experimenting in their garages and built their own. Their company, MountainBoard Sports, was born as orders from friends began pouring in.

The duo’s first distributor was in Japan, where the sport, mirroring snowboarding trends, caught on in 1995, long before it gained acceptance in the United States.

Lee, 31, and McConnell, 36, turned to U.S. distributors after sales in Japan fell off in 1998. U.S. investors took over in 1999, the staff increased from six people to 25, and growth has been exponential since, said Andrea Dowdy, MountainBoard Sports’ vice president of marketing.

The company, now based in Colorado Springs, Colo., has sold about 16,000 boards since 1996; McConnell expects to sell that many over the next year thanks to a network of more than 100 dealers and interest from ski resorts.

This summer, the boards are being featured at about 20 ski resorts, and McConnell expects the number to double next season.

In New England, Killington and Mount Snow in Vermont, Gunstock and Attitash Bear Peak in New Hampshire, and Sunday River in Maine began renting mountainboards and offering lessons this year. Races are scheduled this summer at resorts including Eaton Mountain in Maine, Laurel Mountain in Pennsylvania, Smuggler’s Notch in Vermont and Snowshoe in West Virginia.

There are different kinds of boards for terrain ranging from flat roads to grassy knolls to steep rocky cliffs. Most models used at ski resorts have hand brakes to help beginners as they learn to carve and powerslide to a stop, and for experts who prefer to beeline at high speeds straight downhill.

The boards, which cost between $250 and $400, are proving most popular with skateboarders, snowboarders, wakeboarders, surfers and BMX bikers, Dowdy said. The average speed is between 10 mph and 12 mph, though riders can go faster and can control their speed through tire pressure and turns.

While there are pros who can do 360s, flips and powerslides, hurtle down mountains and soar over jumps, one doesn’t have to be into extreme sports to ride an all-terrain board.

With a little instruction and the right safety gear, most people can figure it out on the first outing.

But there is a reason why safety equipment, including helmets, wrist guards, gloves and elbow and knee pads, is mandated.

On a recent afternoon, a New Hampshire teacher took a spill that resulted in a twisted wrist and a couple of cracked ribs at Sunday River. The bruised and battered novice vowed that he would do it again, however.

Evan Lipstein, whose company produces Mongoose and Hyline all-terrain boards, knows riders as young as 5 and as old as 65.

“It really boils down to what is the terrain that they’re going to be riding on,” Lipstein said. “It is a very good family sport, as is snowboarding and skiing.”

Sunday River mountainboarding instructor Braden Douglass, 16, believes mountainboarding will catch on at ski resorts, just like mountain biking did more than a decade ago.

Douglass is so confident in the sport that he took his mother up the mountain for a run.

“It will soon be more popular than mountain biking, and it hurts less when you fall,” he said.