Ah, that's right! Sonic R has hands down the best areas for irl runs! I didn't even consider them.
They are all very safe, have many routes, and would be a lot of fun! Because they aren't so dangerous they are the most practical for competition. (heh) And they are also good for spectating, as well as swimming, a skate park or just a place to sit and eat ice cream.
Well Mad Matrix takes place in cyberspace. Your body is weightless during the circuit ride things right?... and you would probably be able to go through them even as a human.
That'd look a little funny, wouldn't it? I mean, Shadow's like half our height, not to mention that he curls up a lot tighter. And aren't some of those tunnels a little narrow? Plus, the big thing is spinning (which ieatatsonic mentioned). You'd need a 3rd-person view to get anywhere while spinning.
I figure you don't have to curl up or roll to do that part.
But as for dash plates and springs - I figured they are removed and you have to navigate the stage without them. Or, springs may be replaced with ladders wherever they may be needed to make the stage physically passable for a human.
Just like enemies... but actually you
can keep enemies. Because it's only springs and dash plates that would instantly kill you or are physically unviable. Whereas enemies are just extremely dangerous. But really, in many cases, a human should be able to avoid them. Especially in classic stages because you are never forced to defeat enemies to proceed. Shadow the Hedgehog stages are death traps and Sonic06 crabs would be a slaughter.
But still, no enemies... besides making too many levels impossible, they not really in the intended spirit of the topic if you ask me. A "how fast can you run through Green Hill" topic not a "oh my god, those robot bees are shooting at me everywhere I go and more robots are coming out from inside the walls, i'm bleeding and if I survive I'm scarred for life"
But now that I mention it, we can do a seperate idea for doing levels with enemies. However you will be armed with weapons instead of just yourself. (otherwise you can't kill them) You can have like a pistol or something. We can have infinite ammo.. but better yet, ammo management can be another factor. You may have to carry your own ammo which can slow you down in the non-combat sections of the stage. A common strategy may be to drop all your gear at the final stretch. That just cracks me up.
