BEWARE: Some fitness devices miscalculate progress


runner using armband fitness device

Jan. 21, 2016

SLIPPERY ROCK, Pa. - Now that the holidays are over, many people are looking to shed a few pounds by dieting and kick starting a fitness regimen. Lots of folks begin with daily walks and the purchase of a physical activity-tracking device such as a pedometer or accelerometer to track steps and calories expended.

Research by academics, including Kim Smith, SRU associate professor of exercise and rehabilitative sciences, show that most wearable fitness-tracking devices provide an accurate step count. But many commercially available pedometers do not accurately estimate calorie burning as measured by the kilocalorie (kcal) method.

kim smith


"If the pedometer falsely overestimated kcal expenditure, clients would likely get frustrated with a lack of weight loss," Smith said.

Smith is not the only expert to discover kcal inaccuracies. Gregory Welk, a professor of kinesiology at Iowa State University, carried out research showing return information from portable fitness devices is inaccurate by up to 40 percent. Welk's 2014 study assessed the accuracy of seven popular fitness-tracking devices.

All seven trackers were determined to be off in measuring calories by at least 15 percent. Measurement collected on one device was 40 percent inaccurate, according to a story in Workforce about Welk's research.

Smith assembled a team of undergraduates to help gauge the effectiveness of the devices. Smith and Lauren Murberger, an exercise science major from New Middletown, Ohio, Ashley Sieczkowski, an exercise science major from Lower Burrell, and Jacob Secich, an exercise science major from Hermitage, called their student-faculty research "Accuracy of Three Commercially Available Pedometers in Measuring Step Count, Distance Traveled and Kilocalorie Expenditure."

Smith said kcal is a measurement of the amount of energy in the foods you eat. Low-energy foods have a relatively small amount of kilocalories, while high-energy foods have a lot of kilocalories. In common usage, non-specialists and consumers refer to kilocalories as calories, although these two terms have different technical definitions.

For example, according to the U.S. National Library of Medicine's Medline Plus, a single calorie contains enough energy to increase the temperature of a gram of water by 1 degree on the Celsius scale. A kilocalorie, on the other hand, contains enough energy to increase the temperature of a kilogram of water by 1 degree Celsius. A kilogram contains 1,000 grams, and a kilocalorie contains 1,000 real calories.

"When you eat or drink, your body breaks down the food and beverages in your diet and uses their energy content, or calories, to maintain all of your systems and internal functions," Smith said. "This breakdown and conversion process, called your metabolism, continues 24 hours a day whether you're physically active or inactive.

However, physically active people generally burn through more calories than physically inactive people. A variety of additional factors can influence your body's rate of calorie usage, including your body size, muscle content, gender and age."

The SRU researchers tested three commercially available pedometers: The Omron HJ-720 ITC, the BCF Pedometer and the Yamax Digi-Walker CW-70.

To conduct their research, the team recruited 19 college students. Students wore pedometers on various locations on their bodies and walked one mile on a treadmill. To determine accuracy, walkers wore a portable metabolic analyzer, Smith said.

The first session examined the Omron HJ-720 ITC pedometer. Smith said there were no significant differences between actual steps taken (2,016) and the steps recorded by the pedometer located at the hip (2,131) chest (2,126), back (2,120) or pocket (2,110). She said there were no significant differences in distance walked.

"However, there was a significant difference between actual kcal expenditure (82kcal) and kcal expenditure recorded by the pedometer at the hip (69kcal), chest (69kcal), back (70kcal) and pocket (69kcal)," she said.

"Although the Omron pedometer produced very reliable results regardless of placement on the body, it did not accurately estimate kcal expenditure," Smith said.

The results were similar with the Yamax and BCF, although the BCF pedometer significantly underestimated distance too.

"None of the commercially available pedometers accurately estimated kcal expenditure," Smith said. "As such, significant advancements need to be made in order to develop proprietary algorithms which improve pedometer accuracy. While the development of the algorithms is still a necessity, health care providers may argue that it is better to underestimate kcal expenditure rather than overestimate."

Smith said physical activity monitors have become increasingly popular due to the increase in the number of physical activity recommendations. Pedometers are inexpensive, lightweight and unobtrusive tools that measure physical activity by responding to vertical accelerations of the hip during gait cycles.

She said there are two common types of pedometers: spring-levered and piezoelectric. Spring-levered pedometers typically include a horizontal, spring suspended lever arm that moves up and down with normal ambulation, such as walking or running. An electrical circuit closes with each movement detected and an accumulated step count is displayed digitally on a feedback screen.

beth larouere


Beth Larouere, assistant professor of exercise and rehabilitative sciences, said consumers could best protect themselves by scheduling a consultation with a health fitness professional before buying a wearable fitness-tracking device. The key to making the right purchase, she said, is to determine your individual needs.

It's not a question of buying a "good" or "bad" product, but knowing which product you need.

"A health fitness professional will help guide a purchaser to a the device that will be most helpful to them, based on an indication of what features a person might need for physical activity," Larouere said.

Regardless, the main purpose of any portable fitness device is to promote commitment to lifestyle change and accountability, similar to counting points with Weight Watchers.

She said those on a fitness/weight loss plan should keep a food log and search online for ways to calculate calorie intake versus calorie expenditure.

She said most of the portable devices are excellent and offer upgraded functions such as GPS and heart rate monitoring. Even if not 100 percent accurate in all measures, they help people improve their health.

"For the consumer-based user, they just really want a product to use as a self-motivator for behavioral change," she said.

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