Before
So, when I was a kid we had one of those cheap, unpowered treadmills that was basically just a belt on rollers you ran on.
It also had zero safety measures in place aside from the arm rails, which meant you could hold your weight on the rails and just kick the belt like you were running on air.
It was possible for a 12 year old to get the belt moving over 30 MPH because it just didn't slow down for quite a while after you pushed it. This meant that as a kid who could barely make a 10 minute mile you could, for a brief moment, feel like Sonic the Hedgehog.
It also led several of my friends to brag about running 30 MPH.
After
So when I was a kid, we used to have one of those cheap, non-walking treadmills that were mostly just reel belts that I run on.
There were also no precautions, except for the bars, which means you can keep your weight on the bars and release the belt when you run through the air.
The 12-year-old was able to move the belt at a speed of more than 30 km / h, because he did not have fun long after he was pushed. This means that as a child who barely walks for 10 minutes, you can feel like a dream hedgehog for a short time.
It also made many of my friends brag that they ran 30 km / h.