Two American entrepreneurs have chalked up a big publicity win for their clothing company with an internet ad.

The Instagram spot centres on two key words — hockey butt — and features the shapely rear end of an NHL star.

It debuted with the start of hockey season earlier this week and has gone viral, having been noticed by thousands of people and covered by sports reporters and social media outlets.

"This is the type of stuff you really can't predict," said Lee Moffie, co-founder of State and Liberty, the Michigan based fashion brand behind the ad. "You're just hoping that it resonates with people."

If you've never heard of hockey butt, many online who think you're missing out. They're raving about the 60-second commercial starring Detroit Red Wing Dylan Larkin.

It opens with Larkin confessing he has a "hockey butt" and quickly progresses to a series of strategic slow motion shots showing off the company's close-fitting, stretchy dress pants.

Larkin laments that he can't find off the rack pants to fit him because hockey players "have relatively small waists, and big quads, and big thighs, and a big butt."

That big butt now dominates the imaginations of many Twitter and Instagram users.

I keep singing HOCKEY BUTT HOCKEY BUTT to the tune of Smelly Cat 😕 —@benyahr THAT HOCKEY BUTT AD <a href="https://t.co/tRTvJuofjM">pic.twitter.com/tRTvJuofjM</a> —@megsokay It’s literally all I’ve been thinking about today <a href="https://twitter.com/hashtag/hockeybutt?src=hash&ref_src=twsrc%5Etfw">#hockeybutt</a> —@trizZzden I have a hockey butt and buying pants IS hard! :( —@adammc123 what is elizabeth warren's plan to solve the hockey butt problem —@dannynett

Moffie feels a little guilty about all the attention that his friend and customer Larkin is getting since talking him into doing the ad. He says the crew didn't realize that it would have such sex appeal.

"He's been a really great sport about it," Moffie says.

While only a fraction of those commenting on social media may actually be State and Liberty's target audience, Moffie says a large number of athletes are looking for clothes to suit their bodies.

When a problem becomes an opportunity

Before turning hockey butt into a hashtag, Moffie and his friend Steve Fischer turned an idea into a company.

The two athletes met while attending the University of Michigan. Moffie was on the school hockey team and was actually drafted by the San Jose Sharks in 2010.

The pair found they had a common problem finding dress clothes that fit them properly. In 2015 they began making dress shirts for more muscular bodies and selling them online.

Lee Moffie, left, and Steve Fischer founded State and Liberty Clothing Company in 2015. Moffie says they couldn't have predicted their 'hockey butt' ad would go viral on social media. (State and Liberty Clothing Company)

Recognizing there was a market for more than shirts, the business evolved into "dress clothes made for athletes." State and Liberty makes formal-style garments made from a blend of polyester and spandex that feels and flexes like workout wear.

The formula seems to be working.

State and Liberty's Instagram feed features a number athletes sporting the brand's threads, including NHLers sporting the brand's threads including Mitch Marner, T.J. Oshie and Brad Richardson. Even super fit Hollywood hunk Chris Pratt is a customer, Moffie says.

The athletic body business

It's widely known that the athletic apparel industry is massive. Just look at Lululemon's nearly $25 billion market value.

A lesser known fact is that athletes and people with larger body parts want more fashion options than sweat pants or leggings and a hoodie.

Beyond '"hockey butt," thick arms, legs, and chests can pose a problem for some athletes and non-athletic body types to buy clothes off the rack.

That's beginning to change.

Now Lululemon itself offers dressy athletic fit pants for men. RW & CO. and is offering athletic fit shirts, pants and suits, while Le Château features athletic fit men's shirts. An American startup called Barbell Apparel is offering athletic build casual clothes for men and women.

Americans were not the first to grab the 'hockey butt' business. Gongshow, a Canadian company, claims to have invented hockey jeans in 2012. (Gongshow)

ESPN focused on the problem earlier this year in an article headlined "the struggle is real." It documented hockey butt in detail and quoted NHLers describing just how hard it is for them to find a pair of jeans at any price.

The struggle for properly fitting denim is something U.S. hockey equipment maker Bauer has taken a shot at solving with its hockey jean line, "designed to fit the more robust thigh and butt of a hockey player."

Gongshow, a Canadian company which makes "lifestyle hockey apparel" claims to have invented hockey jeans in 2012, closely covering our posteriors in patriotism.

Will hockey butt be a winner?

Experts say that an ad going viral doesn't automatically boost company sales, even when it delivers a good laugh or a smile.

"You certainly don't want the brand name to get overshadowed," says June Cotte, a marketing professor with Western University's Ivey Business School in London, Ont.

June Cotte, a marketing professor with Western University’s Ivey Business School, says sometimes a brand can be overshadowed by its own successful viral ad. (Shawn Simpson, SWS Photography)

"I think that the placement of the brand name was pretty clever, in that it is on one of the butt shots," she says. "People will watch that ad all the way to the end, I'm sure. And the brand will be reinforced."

Simon Creet, chief creative officer of Toronto ad agency The Hive, described the spot as "terrible and amazing all in one."

That kind of work actually cuts through these days. I think most consumers are kind of tired of having super slick, polished messages put in front of them. - Simon Creet, Chief Creative Officer, The Hive

Creet found Larkin's performance stiff and the slow-motion shots too obvious.

A men's league player himself, he believes the ad will connect with all kinds of athletes because it has an authenticity that's in keeping with the small company that made it.

"That kind of work actually cuts through these days. I think most consumers are kind of tired of having super slick, polished messages put in front of them."

Moffie says the whole ad was shot in less than an hour. He's not sure if they'll do a hockey butt sequel next year.

There are bigger sports to think about for the U.S. market. He and his partner Fischer are planning new designs.

When the pair were looking for capital to fund their fledging business, some potential investors told them athlete fit market wasn't big enough, Moffie says.

Now that their line includes pants, jackets and suits and stores in six U.S. cities, as well as Toronto, Moffie believes they've scored.

"We're definitely proving that the market's big enough."