Illustration by Jim Cooke.

A team of researchers rode a roller coaster more times than they probably care to remember, just to figure out why roller coasters trigger the passage of small kidney stones. With the further help of a 3D-printed model of a kidney filled with urine, they think they’ve solved the puzzle.


In the new study, published in the Journal of the American Osteopathic Association, urologist David D. Wartinger and his colleagues at Michigan State University College present evidence to support widespread claims that riding a moderate-intensity roller coaster can help people pass small kidney stones. The results, though still preliminary, could assist in the development of a rather unconventional therapy for patients.

Kidney stones: The bigger they are, they harder—and more excruciatingly painful—they are to pass. (Image: G.L. Kohuth, Michigan State University)


Kidney stones are a mass of chemicals and salts found in urine. Passing kidney stones can be an excruciating experience, particularly when the stones are large. Getting them out early before they get too large is key to reducing much of the discomfort and risk.

Prior to the new study, virtually no one took the time to figure out what prompts a kidney stone to pass through the urinary canal, though urologists are familiar with some common triggers.

Pregnant women often pass kidney stones, the result of increased vitamin intake. Physical labor will sometimes loosen it, as will bungee jumping, bouncing on a trampoline, dirt bike riding, and even a violent sneeze. The fact is, scientists haven’t been able to isolate a single trigger—but roller coasters seem to play an important, and even reproducible, role.

“When a series of patients returned from spring break with stories of passing a kidney stone after riding the Big Thunder Mountain Railroad at Disney World in Orlando, I started to wonder if we had a unique opportunity to help patients,” Wartinger told Gizmodo. “The moment one of my students and I realized we had to move forward was hearing from a patient who rode the ride three times and after each consecutive ride he passed a stone.”


A silicon cast of a kidney. (Image: G.L. Kohuth, Michigan State University)

Wartinger and study co-author Marc Mitchell used 3D printing to create a clear silicone anatomical model of this particular male patient’s kidney. They filled the model with the patient’s urine, and placed three kidney stones of various sizes in the upper, middle, and lower passageways of the simulated kidney. After sealing the model, the researchers set off for Disney World.




With the permission of park officials,the researchers placed the model of the kidney in a backpack. Then they hopped on the Big Thunder Mountain Railroad ride, holding the kidney model between themselves at approximately the position of a real kidney to stimulate the forces that would be felt by a real person. They repeated this 20 times, collecting important data with each run. Then they repeated the experiment on Space Mountain and the Walt Disney World railroad, for a total of 60 rides.

“As far as having to ride the coaster repeatedly, honestly, the first five to six times were great. By the end we were just gritting our teeth and wishing to be done.”


“As far as having to ride the coaster repeatedly, honestly, the first five to six times were great,” said Wartinger.”By the end we were just gritting our teeth and wishing to be done.”



At least for this patient’s simulated kidney, the data showed that sitting in the back of Big Thunder Mountain Railroad resulted in a stone passage rate of nearly 64 percent. Front seat rides produced a passage rate of nearly 17 percent. The researchers say that powerful and random forces jarred the stone lose, guiding it through the passageway.


“A kidney looks like a tree with branches,” said Wartinger. “The forces move the stone from being positioned where a leaf is located, down through the branches and out through the trunk—and onward to the bladder. It’s not surprising that the model we used passed kidney stones on this coaster because it’s based on a gentleman that passed three stones on this exact roller coaster.”

Big Thunder Mountain Railroad at Disneyland in Orlando. (Image: CC-BY 2.0


Wartinger believes this can be replicated, but not everyone will respond to the same ride. Like a fingerprint, each person has a unique kidney passage pattern, so everyone is going to have their own “ideal” kidney stone-jostling roller coaster ride. And for some, other activities may prove to be more effective.



The researchers believe that these findings can translate to preventive care, and be of help to three distinct groups.


“If you have a stone smaller than four millimeters it can help you pass it before it becomes obstructive or large enough to become stuck in the tube,” said Wartinger. “When stuck it may require emergency surgery and will cause extreme pain.”

Indeed, many have compared the pain of passing a large stone to natural childbirth. He says it could also help people who have a procedure that smashes a big stone into smaller stones, who can then pass the smaller fragments with the help of a thrill ride. Finally, it can help young women clear small stones before they become pregnant (it’s not advised that pregnant women ride roller coasters).


Looking ahead, the researchers would like to test more models on a range of other coasters, assuming they can get access to additional theme parks. And to make these findings truly helpful for patients, the researchers would need to conduct ultrasounds of individuals before and after each ride.

The study is also pertinent to space exploration. The effect of gravity normally helps with the passage of kidney stones, which is why so many astronauts suffer on the International Space Station. “Kidney stones will truly be a challenge for people on Mars 1,” said Wartinger.


[Journal of the American Osteopathic Association]