How Accurate Are Today's Pocket Pedometers?

Pocket Pedometers Put to the Test

Omron HJ-320 Pedometer
Omron HJ-320 Pedometer. Courtesy of Amazon.com

Pedometers are getting better and smarter, but are they really counting all of your steps? The old spring-lever or coil mechanisms had to be positioned perfectly on the waistband in order to count steps accurately. But many pedometer companies switched to tri-axial piezoelectric pedometer mechanisms that aren't so fussy and can be worn in many positions or carried as a pocket pedometer. Meanwhile, wrist-based fitness bands using accelerometer chips became popular.

See a study of how accurate fitness bands and apps are in counting steps and in counting calories.

Pocket Pedometer Accuracy Study

Researchers at the University of Texas at Austin put five pocket pedometers to the test. Would they count steps accurately no matter where they were positioned? Would walking speed or terrain matter?

They used forty test subjects who were of different ages and weights. They tested each pedometer whether it was placed on the waist, the chest (many women like to clip their pedometer to their bra or wear it on a lanyard), on an armband or in a pocket. They also counted each step using a hand-tally counter, so they knew how many steps were actually taken.

Pedometers Tested:

They selected the pedometers to represent mid-level pedometers used by corporate fitness programs.The study was supported by a grant from Omron Healthcare Inc.

Does Speed Affect Pedometer Accuracy?

They tested the pedometers at speeds from very slow (2 mph), moderate to brisk (3 and 4 mph) up to a jogging speed on a treadmill (6 mph) and outdoors at a self-selected speed on pavement.

The bottom line was that all of the pedometers were accurate within 5% at moderate walking speeds and when worn on the waistband, a lanyard around the neck, or on an armband.

But they all counted slightly fewer steps than were actually taken at any speed, about 5%. This is likely the result of the error-correcting programming built in to eliminate random movement or "junk steps." That's a difference of 500 steps if you walk 10,000 steps, or a quarter of a mile in 5 miles.
How Many Steps are in a Mile?

This error got slightly worse at slow walking speeds. If you usually walk very slow, at over 30 minutes per mile (2 mph), then these pedometers are probably under-counting your steps by almost 8% instead of 5%, or 800 steps in a 10,000 step day, 400 steps in a 5000 step day.

They also under-counted more at very high walking/jogging speeds, about 6%

Do Pedometers Count Accurately in a Pocket?

The pedometers counted fewer steps when carried in a pocket or purse. While these pedometers are often marketed as pocket pedometers, you are probably walking more steps than they count if you aren't wearing them on your body. The difference is still small, between 7-8% If you carry your pedometer in a pocket the difference would be only about 750 steps in a 10,000 step day.

Are Pedometers Missing Lifestyle Steps?

The researchers also noted that the two Omron models tested have a built-in filter that only adds steps to the total if you have been walking for more than four seconds. It is common for pedometers to have these junk step filters. But they say in our everyday life we often take only four to six steps in a row as we move around the house, etc. These pedometers wouldn't count those steps into the total. The Virgin GoZone pedometer doesn't have a filter and it was the least-accurate pedometer, usually over-counting steps.

Bottom Line

For the best accuracy, wear a pedometer attached to your body rather than in a pocket. Know that your pocket pedometer may be counting slightly fewer steps. But the difference matters less if your intent is simply to motivate yourself to move more and increase your total step count.

Source:

Wonil Park, Victor J. Lee, Byungmo Ku, and Hirofumi Tanaka. "Walking Speed and Placement Position Interactions in the Accuracy of Various Newer Pedometers." Journal of Exercise Science and Fitness, online April 3, 2014

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