In the US$28-billion (S$38.4- billion) sneaker industry, Athletic Propulsion Labs (APL) is an unlikely success story.

The seven-year-old brand was started by basketball-playing twin brothers, Ryan and Adam Goldston, who were looking for a way to jump higher than their friends.

The twins, who turn 29 next month, spent five years designing a basketball shoe with compression springs that enables its wearer to jump up to 9cm higher.

The fledgling brand received a big lift when the US National Basketball Association (NBA) banned the shoe in October 2010 because it said the sneakers give wearers an "unfair competitive advantage".

The rest is retail history: The ban made headlines and the sneakers started flying off the shelves.

Nine months worth of inventory was sold within three days and celebrities such as reality television stars the Kardashians and professional boxer Floyd Mayweather were spotted wearing APL shoes.

Today, APL shoes are sold by high-end retailers such as Saks Fifth Avenue and Barney's New York in the United States and Lane Crawford in China and Hong Kong as well as by online luxury fashion retailers Mr Porter and Net-a- porter and at APL's own website, www.athleticpropulsionlabs.com.

The APL line also includes running shoes and the brothers will be launching a line of made-in-Italy "lifestyle" shoes made of leather and suede later this year. A clothing range for men and women was introduced last year in response to demand for a "head-to-toe APL look". Female customers account for up to 65 per cent of APL's sales.

The siblings were in town two weeks ago to promote the launch of APL at luxury shoe and accessories retailer Pedder On Scotts in Scotts Square.

Although the identical twins were dressed in similar T-shirt- and-jeans outfits for the interview, they were easy to tell apart: Adam sported a full beard and trendy undercut hairstyle while Ryan was clean-shaven. And, of course, they were wearing APL shoes.

The 1.8m-tall twins, who played competitive basketball at the University of Southern California (USC), came up with the shoe design in their freshman year in 2005. Ryan majored in business and Adam studied sociology.

"We always did everything we could from a training perspective to increase our athletic performance, but there was never anything that could give us an instant increase," explained Ryan.

"When we're playing against guys that are six feet 10 inches, or seven feet tall, every inch matters."

Six feet 10 inches is about 2m tall.

The brothers developed a shoe prototype based on the idea of a sandwich-like compression spring at the front of the shoe under the ball of the foot. At one point, their dormitory room was littered with "over 1,000 springs".

Once they were happy with the prototype, they sent it to manufacturing companies in China and Taiwan to make the product.

The bachelors founded APL in 2009 and launched the Concept 1 basketball shoes with their patented Load N' Launch springs shortly after graduation in 2010.

Originally starting with four employees, the company now boasts 15 employees at its Los Angeles office. The designs of the shoes and apparel are done in-house, with logistics and manufacturing outsourced to countries such as China and Portugal.

The brothers decline to reveal sales figures, but said that business has more than tripled from 2014 to last year. Prices start at $250 for a pair of running shoes to $360 for a pair of basketball shoes.

A pair of Nike Flyknit Racer shoes cost about $250, while adidas basketball shoes cost between $170 and $250.

While APL has built a reputation for producing shoes that marry form and function, the twins said the technical performance of the shoes has always been their first priority.

Ask them about the design of their footwear and they can go into details such as using "3D stretch knitting" in their shoes so that customers can feel comfortable wearing the sneakers without socks.

Ryan said of "3-D stretch knitting": "Basically, it moves dynamically with your foot, so if you flex your big toe, the knitting stretches with that, but stays tight everywhere else."

It is clear that the twins place a lot of emphasis on innovation and technology and enthusiastically cite laboratory tests which back the performance claims of their shoes. They have six patents on the technology used in their shoes and come up with different iterations of the shoes to suit different wearers.

Adam said: "A lot of people buy our shoes because they think they look good. But technologically, we're second to none so we get a ton of competitive athletes purchasing our products and wearing them."

One could say that the twins had a foot in the sneaker industry when they were young.

Their 61-year-old father Mark Goldston helped create the famous Reebok Pump sneaker in 1989, which had an adjustable inflatable cushion around the ankle for a custom-fit.

He was also president and chief operating officer of American lifestyle brand LA Gear in the early 1990s and helped develop the wildly popular LA Gear Lights shoes.

Their mother worked in the advertising and design industry and founded fashion website www.theblondeandthebrunette.com.

Mr Goldston, now a venture capitalist, roped his sons into testing the shoes he worked on, including getting them to try out the L.A. Lights which had flashing lights.

The twins said their father has been an invaluable source of help when they were starting out.

Adam said: "Having access to someone who's as smart as he is business- wise has helped us in terms of scaling the brand on a global scale."

Their dad's entrepreneurial spirit has rubbed off on them. Ryan said of the early days: "We were starting out so we had nothing to lose because we didn't have an established career. And if we failed, we would not have fallen from very high."

Being inexperienced also had its advantages, he added. "It allows you to look at something from a fresh perspective and not be really clouded by what's been done before. So we felt like, 'Someone's got to create it, why can't it be us?'"

Being brothers has helped in their working relationship. Disagreements are smoothened over a game of ping pong.

Adam said: "We're brothers first, so it helps to know that you can't get rid of each other. It's definitely a lot easier and it's to our advantage that we're twins."

However, they do have their differences. "I'm more detailed and focused," volunteered Ryan.

"Ryan will tell you every single detail of something," Adam said with a laugh. "It's my nightmare."