Montana State University

Hip-riding pedometers are popular, but how accurate are they?

May 2, 2005 -- by Carol Flaherty


Dan Heil in his office at MSU. Photo by Carol Flaherty   High-Res Available

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Pedometers -- those hip-hugging calculators of footsteps and miles -- have become the boomer generation's symbol of striding toward healthy maturity.

Walking is recommended for everything from mild depression and high blood pressure to osteoporosis and diabetes. It is also one of the most-often-recommended forms of exercise for healthy adults, says Dan Heil, Montana State University exercise physiologist. And for walkers, pedometers are a way of keeping score.

"Pedometers are simple and contagious," Heil says. "Once you start watching how much you walk, it becomes interesting. You want to know how many steps you've taken."

For scientists, pedometers have an added dimension.

"Pedometers have bridged the gap between being useful in exercise studies and being reasonably cheap, so they've become very popular with clinicians," he says.

However, the accuracy and longevity of pedometers has been largely unknown, so Heil designed a study to see how long three different pedometers would remain accurate under normal walking conditions.

"It's a logical first question," Heil says. "If we assume pedometer accuracy when they are new, how long do they last?"

He decided to first test three brands: one given away free by a fast-food chain and two others that each cost about $30. That study has been completed, and another test, this time of 15 brands or models, will be completed later this year.

Heil says that before he could do the study, he had to design a way to simulate walking so all of the pedometers faced the same test. He came up with a rack, a sort-of two-winged shaker, with pedometers lining each wing. Hooked up to a motor, the pedometer-laden wings gently shake and shake through hundreds of thousands of "steps" at the equivalent of about three miles per hour.

"We shake the pedometers 100,000 to 200,000 steps, then take each off and wear it on a treadmill to see if it is counting accurately," Heil said.

A common goal for walkers is 10,000 steps, or about four miles, a day. With that used as a baseline, the free brand would last about six months. A Sportline Electronic would last for 710,000 steps or 1.4 years. A Lifestyles Digi-walker was still accurate after 2.4 million steps or about 4.5 years of walking.

"We stopped the test at that point, so we don't really know how much longer the Digi-walker would go," Heil says. He adds that there are two take-home messages from the study, one for the walker and one for the scientist.

For the walker, it's important to realize that pedometers wear out. With the models tested so far, the wearing out occurs "with a whimper, not a bang." Aging pedometers counted fewer and fewer of steps rather than not registering at all.

"That's important if you are seriously trying to meet walking goals. After a time, if you are no longer reaching your goals, it would be frustrating," Heil says. "That's important to know, so that after six months to a few years, you know that you may need to compare your pedometer to a newer one."

For researchers, it's even more important. It means they must verify the accuracy of the pedometers used in tests.

An additional pedometer variable is how much impact is required to get a step to register.

"Walkers will want to consider the sensitivity of several pedometers," Heil says. "Some people are 'soft walkers.' A person with a very soft step will need a pedometer that is quite sensitive. However, that same pedometer may register simple rocking back and forth and may not be as useful to researchers trying to measure "meaningful walking."

The way a pedometer is made also influences its longevity, he adds.

"Virtually all pedometers that cost less than $15, are given away free or are included with books and flyers on walking for exercise, are designed with a hair spring mechanism," he says. "The hair spring is what controls the movement of an internal pendulum for counting steps. It seems that this hair spring mechanism is really cheap to include in a pedometer and is why so many inexpensive and free pedometers "die" within six to 12 months. Higher quality pedometers use either a coil spring mechanism or a piezo-electric device that eliminates internal moving parts altogether."

Whether you are in search of health, or just like to keep score, checking your pedometer accuracy after a year or two of use may help you keep motivated as you walk for a healthier future.

Contact: Dan Heil (406) 994-6324