What it was: The vibrating exercise belt. If there's anything that sums up our condescension for fitness fads of the past, it's these contraptions. Go to YouTube and search for "Mueller Exerciser Belt," and you'll find a herd of stout men looking humiliated and uncomfortable as wide leather straps jiggle their avoirdupois up and down. Set the clip to "Yakety Sax"? Comedy gold.

How it worked: Surely people wouldn't have subjected themselves to the indignities of looking like Jell-O in an earthquake if it didn't take off some weight, right? Surely it wouldn't have lasted from the 1930s to the '60s if there weren't breathless testimonials from people who went from stout to lean. So why did we stop using them?

Because they didn't work.

What the idea was: If you vibrate the fat, it will break down, and your body will magically flush it away. As if there's some special type of cell in your bloodstream that says, "Oh, here's a fat particle. Better get that down to shipping ASAP."

It made sense to the credulous, but I'm guessing most of the people who used it for decades did so because it was regarded as exercise, required nothing but standing, and left you feeling tired — like exercise should.

What happened to them?: Nowadays the idea of high-speed belly jostling seems as quaint as a gym where men in handlebar mustaches throw medicine balls at one another. But, in case you haven't noticed, handlebar mustaches are back. As are medicine balls.

That might explain the wide range of vibrating fitness products on the market now, from belts to stand-on machines. They range in price from $30 to more than $2,000.

Recommended for: People who like to look like Jell-O and make funny sounds.