By Rob Boffard, Wired UK

Get Corli Du Toit talking about her sport and you’ll start hearing about axles, bearings, silicon, metal alloys, rims and hubstacks. But she isn’t a cyclist or a skateboarder. She’s a professional yo-yo thrower, and comparing her collection of yo-yos to the traditional toys is like pitting a Formula 1 car against a wood go-kart.

Competitive yo-yoing has seen huge growth worldwide in recent years, and the science of building a better yo-yo has become incredibly complex. That Duncan you threw a kid? Pfft. Child’s play.

“Most yo-yos these days are metal, or a heavy plastic called Derlin,” South African-born Du Toit says, gesturing to the yo-yos laid out on the table in front of her. She picks up a small green, metal number and turns it around in her hands. “It’s all about reducing friction, and making sure that the yo-yo spins for as long as possible.”

Abruptly, she stands up, and begins “throwing”. Walking the dog has no place here: This all about chaining together complex, flashy, high-speed tricks. The yo-yo spins, doubles back on itself, and then Du Toit turns the string into an impossible cat’s cradle before dropping the yo-yo into it and yanking it back out again.

Weight is key to a maneuverable yo-yo, says Du Toit.

“Extra weight on the outside rims will give a longer spin time, but push it out too far and the yo-yo may wobble,” she says. “The balance between weight and design is a closely guarded secret which each company seems to have to figure out for themselves.”

She’s not kidding. Several companies we contacted politely declined to discuss their design processes.

A fully-built professional yo-yo can cost more than £100 ($156). And these aren’t the yo-yos you’re used to. Old-school yo-yos — and those you see in toy stores — are looping models designed to return to your hand after a throw. Current designs let the yo-yo “sleep” at the bottom of the string, spinning in place, which allows the execution of tricks.

To keep spinning, yo-yos rely on reducing friction. To do this, they feature an axle wrapped in a machined concave bearing. If a thrower wants to bring the yo-yo back up, he or she must jump the string onto the yo-yo’s response system: a pair of rough silicon bands at the edge of the bearing that catch the string and start looping it around the bearing.

Modern high-tech yo-yos have a cross-section shaped like a butterfly, unlike the original curved “imperial” shape of old-school yos. Aluminium alloy is a favored material. And then there are the accessories, like hubstacks, which are grips you can attach to the ends of an axle, allowing you to hold the yo-yo as it spins. Even strings — often made of high-grade polyester — offer a wealth of choices. And once you’ve bought a yo-yo, you’ve got to maintain it and lubricate it.

“Yo-yos are now made as precision tools rather than mass-market toys,” says Simon Welch, head of the British Yo-Yo Association, which regularly holds events throughout the UK. “They spin a lot truer and a lot longer, and feel like professional tools.”

In contests, competitors do a set routine to music, competing in categories which use different yo-yo models. While there’s not a lot of money in competitive yo-yoing, there are regular events worldwide, and an active network of companies prepared to sponsor both them and the thrower themselves.

Surprisingly, the sport is young, having only really come into being in 2003. Du Toit started yo-yoing in 2008, and although she’s had to put in a huge amount of practice, she laughs when asked how much time she spent untangling strings: “You don’t get tangled strings. Not when you use one yo-yo. But when you use two…”

And she’s off again, grabbing two yo-yos off the table and flipping them into a high-speed trick routine. Yo-yoing might still be finding its way as a sport in 2011, but the pros certainly now have the tools to make it happen.

Photos and videos: C3 Yoyo Design