Watching the gymnastics in the Olympics, I am reminded of the good old days when I was peripherally involved in the sport. My event was trampoline, and I wasn't very good at it at fourteen -- the little girls are doing things on the floor I couldn't do on the trampoline in my wildest dreams ...
But back then, circa 1960-61, there was a brief phenomenon that I recall as the Jump-Jump Trampoline Center, on Plank Road, not far from Prescott Junior High. Part of a nationwide chain of such places, Jump-Jump consisted of a series of in-ground trampolines -- that is, big pits were dug in the Earth and covered with rectangular nylon decks, probably eight feet by ten or twelve. You paid for these by the hour -- cost a dollar, as I recall -- and you were then allowed to bounce to your heart's content.
As I recall, there were sixteen of these, four across by four long.
There was a bit of padding over the springs, but no nets, spotters, or other safety gear.
I had a buddy who was a fairly good gymnast -- first guy in the country in the junior division to do eight bounding backs on his mat tumbling run -- and he and I used to go to the Jump-Jump. On a good day, after it had rained and the pits were half full of water they hadn't pumped out yet, a big bounce would put the deck into the fresh pond under it, which we thought was hilarious.
On a really good day, we'd have the place to ourselves, and although you weren't supposed to do it, we could bounce from one trampoline to the next, trying to see who could do the best tricks along the way. Bored guy running the place would say, "Hey, you aren't supposed to do that." To which we'd say, "It's okay, we're gymnasts." And he'd shrug and look the other way.
I cannot imagine what the liability issues of such a place would be today, and I doubt you could buy insurance from anybody at any price to cover patrons.
Jump-Jump eventually got sued out of existence, even back then, what with broken this and sprained that, as people who had no clue what a trampoline was paid their fees and then promptly bounced off onto their heads on the hard ground. (First thing we learned in class was, never, ever, jump without spotters, and if you were a spotter, your job was to keep whoever was bouncing from hitting anything but the deck.)
"Assumed risk" back then had a much different meaning than it does today, I expect. Nowadays, everything from hair dryers to handguns come with warnings stenciled on them ...