[avip]

Seconded. It takes serious mileage and time to regain full fluency. I am sure this is measurable - I actually fell once after a few years break, as I was not used to manoeuvring between cars. It's like saying "you don't forget how to play the piano". Well you don't, and you do, depends on how you define the "knowing" discussed - something the article did not do for obvious reasons.

[coldtea]

"Forgetting to ride a bike" is not about fluency. Of course you'll lose the fluency if you were advanced biker at some point.

It's about forgetting HOW TO RIDE, the very basic trick of balancing the bike.

[stinos]

the very basic trick of balancing the bike

Which is exactly the point the OP makes to that sentence as if we never stopped biking I think. At the least I'd say it's worded incorrectly. Sure your brain remembers the key part of how to do it, but the finer motor skills, balancing in hard situations etc don't just come back from one instance to the next and take extra practice.

[coldtea]

I don't think anyone seriously says that e.g. a biker doing hard mountain bike rides or bicycle stunts etc will be as good after a 10 year hiatus in which he never touched a bike.

[jplayer01]

Bike riding isn't special. Like every skill you learn, your proficiency will suffer if you don't practice it. That doesn't mean you will entirely forget how to apply that skill, even if lack of practice means you've lost proficiency.