CHICAGO — Researchers are tripping seniors on purpose, and it's not some kind of warped practical joke.

The experiment is among techniques being studied to prevent falls, the leading cause of injury in older adults. Falls in the elderly cost $30 billion yearly to treat and can send them spiraling into poor health and disability.

Conventional efforts to prevent falls include exercises to boost strength and balance, but researchers at the University of Illinois in Chicago are trying a completely different approach. It's based on promising, preliminary results with a lab-built walkway that causes people to unexpectedly trip, as if stepping on a banana peel.

Now the same scientists are testing a similar approach with computerized treadmills. If it works, they envision specially designed treadmills in doctors' offices, clinics and physical therapy centers for training people how to avoid falling.

Clive Pai, a physical therapy professor leading the research, calls the method a potential “vaccine against falls.”

Standard fall prevention techniques aim to improve physical condition by strengthening certain muscles and improving range of motion. And they may require dozens of sessions to be effective, Pai said. His research is focusing on building subconscious learning, and evidence so far shows it can happen surprisingly fast.

“This is all implicit learning. We don't give any instruction. They don't have to be motivated — they're naturally motivated because they don't want to be on the floor,” he said.

Pai has a $1 million, five-year grant from the National Institute on Aging to study and develop the treadmill system, and plans to enroll 300 participants in the next five years.

The scientists demonstrated the technique recently in Pai's lab with 81-year-old Mary Kaye, who had participated in the preliminary walkway research. Graduate students taped little sensors to Kaye's arms and legs that allowed her movements to be tracked and analyzed. Then she was hooked up to a harness attached to an overhead cable to help her remain upright if needed.

First, she used the walkway, striding several paces before a student clicked the computer mouse to make a sliding walkway section move suddenly under Kaye's feet. Kaye stumbled slightly, but kept her balance.

Pai's preliminary research, published in June, found that 24 similar “trips” in just one walkway session taught older adults to learn to catch themselves and reduced their chances of falling outside the lab, during everyday living, by 50 percent up to a year later.

Back in the lab, Kaye next tried the treadmill, set at a steady walking pace that was occasionally interrupted by sudden brief skips. Kaye stumbled at each jolt but managed to stay afoot. Pai thinks Kaye's training in the previous study may have helped keep her steady.

Retired from the travel industry and public relations, Kaye is fit and healthy and looks a decade younger, but said she still occasionally falls — even after the training.

“I land on my face and it's usually quite disastrous — for my face. But I recover and I try to get through another season,” she said.

Older people are at risk for falls for many reasons, including age-related muscle weakness, vision problems and medication issues including side effects and improper doses.