When Zumba Fitness first released last November, it sold so few copies it didn't get close to breaking into the UK top 40, let alone a sweat.
Fast forward seven months and it's celebrating a remarkable fourth week in a row at number one. Last week it outsold the rest of the top five put together, leaving the likes of Lego Jack Sparrow and Cole Phelps trailing behind, gasping for breath.
With over 34 million Balance Boards shifted by the end of last year, the lure and long tail of fitness games, particularly on Wii, was already well understood. When coupled with current real-world fitness fad of Zumba - endorsed by the likes of man-armed pop pensioner Madonna - it's little wonder this branded tie-in is flying off shelves with the force of a million middle-aged pelvic thrusts.
In truth, as a 32-year-old male video games journalist, there's more chance of me getting dressed before midday than turning up at a real Zumba class.
But that, broadly, is why I've long been a vigorous advocate of the potential of interactive fitness: the First World is getting fatter, child obesity is a ticking time bomb, and a gym full of preening, bicep-kissing meatheads will never be a comfortable environment for someone uncomfortable with their physical appearance.
Philosophically, the creators of the Latin dance craze seem to be on the same page as Nintendo. "Are you ready to party yourself into shape?" is Zumba's motto: like Wii Fit, it's focused on fitness through fun, not joyless toil.
The problem with Zumba Fitness, though, is that the implementation of this philosophy is so lazy you'd probably do as well to parade in front of a YouTube video than invest in a game with questionable interactivity and, in the case of the Xbox 360 version I tested, the most spectacularly awful Kinect interface yet.
Let's get this out of the way first. Developers have been experimenting with Kinect controls since it launched late last year. Dance Central got it right with a swipe, while Microsoft's first-party line-up settled on an inferior point-and-hold solution.
Zumba Fitness - an early title for the hardware, so one that does not enjoy the benefit of hindsight - offers the worst of both worlds. Hold the cursor over an icon to lock on, then swipe horizontally to move between options: what sounds sensible in principle is demented in practice.
Swipe too far, too fast (very easily done) and you'll whizz past the option you want, frequently resulting in a patience-fraying back-and-forth.
How this idiotic system made it from idea, to prototype, through testing and into a box on a store shelf is beyond me. Being amongst the first wave of titles is no excuse: never has Kinect seemed a worse substitute for a real controller. Which, though you'll be reaching for it in seconds, cannot be used as an alternative. You Are The Controller (Whether You Like It Or Not).
Now that's off my chest, onto the game. Zumba Fitness offers 30 individual, officially-approved Zumba routines, filtered by difficulty (beginner, intermediate and expert), which can be tackled individually or as part of more elaborate workouts - the longest being the aptly-named, 60-minute Zumba Marathon.
Move-by-move tutorials are an essential port of call for Zumba n00bs and those, such as myself, with the rhythmic grace of a dead-legged drunk. But there's a problem: whilst the often complex steps are sensibly broken down into their constituent parts, the game rattles through them far too quickly, seemingly arbitrarily deciding you've mastered the previous steps, irrespective of your own performance.