Parachutist’s landing best reduces hip impact whether you jumped from an airplane or tripped on a curb
July 7, 2008 – Senior citizens could reduce their risk of hip fracture by nearly 70 percent if they learn to fall like skydivers, new research from the University of Michigan suggests.
In the first study to examine the effectiveness of different sideways fall strategies, computer simulations showed that the parachutist’s landing method best reduces hip impact whether you jumped from an airplane or tripped on a curb.
The parachutist’s strategy involves crouching, leaning so that the outside of your lower leg hits first and then rolling onto your backside. In the simulations, landing in this position subjected the hip to just 25 percent of the force necessary to break it.
“A hip fracture can mark the beginning of a downward spiral. If you fall and break a hip and you’re over 65, you have a 20 percent chance of not surviving another year and another 20 percent chance of not regaining your mobility,” said James Ashton-Miller, a professor in the departments of Biomedical Engineering and Mechanical Engineering. Ashton-Miller is an author of a paper on the research published in the Journal of Biomechanics.
“In this study, we asked whether it matters what you do in the air after you start to fall. We found that a parachutist’s landing style reduces your risk of injury, and you can land a fall safely with or without your hands,” he said.
A hip fracture often occurs when a person trips and lands on his or her side, Ashton-Miller said. The study showed that the typical reduction in muscle strength that occurs with age does not impair an individual’s ability to accomplish the safest strategy.
The study also found that reaction time is as important as the body’s position during a fall. A delay of more than two-tenths of a second in deploying the parachutist’s strategy increased the impact force of the fall by at least 70 percent.
Falling on a non-slippery surface, you have seven-tenths of a second from stumble to impact, Ashton-Miller said. Typical reaction time is two-tenths of a second. That leaves five-tenths of a second to put the fall strategy into practice. So it’s best to know how to fall in advance.
“When you start to fall, you need to know what to do. You can’t hang around trying to decide what to do. What people tend to think is that there’s no time to do anything, and that’s absolutely not true,” said Ashton-Miller, who says he learned this firsthand as an avid skier.
The researchers tested four fall strategies. The “broomstick” strategy involved keeping the body stiff. This was the control. The “hip lateral flexion” strategy allowed the hips to swivel by 30 degrees but the other joints remained stiff. The “spine and hip” strategy confined the knees to a maximum bend of 20 degrees, but other joints could operate normally. And the “free” strategy allowed all joints to move freely.
When a computer simulation of a man falling was given these constraints, it identified the free strategy as the least likely to break a hip. And it pinpointed the parachutist’s style as the best way to allow the joints to move so the muscles dissipate energy and thereby lower the impact force. Ashton-Miller said future experiments and simulations will study women falling as well, and he expects the results to be similar.
Strategies were tested with and without the use of an arm to help break the fall. And time delays of one-, two- and three-tenths of a second were simulated, along with the effects of age on muscle strength.
Source: This research was funded by the U.S. Department of Health and Human Services. The paper is called “Effect of pre-impact movement strategies on the impact forces resulting from a lateral fall.” Ashton-Miller is a research professor in the Institute of Gerontology and in Internal Medicine at the U-M Health System.