Study questions accuracy of activity trackers

Misfit Shine was the most inaccurate at 30.4 per cent error rate while BodyMedia Core was the top performer with a rate of error of 15.3 percent.

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A new study by Iowa State University researchers has questioned the accuracy of activity trackers based on experiments conducted on four different trackers currently available in the market.

Researchers say that though activity trackers are good at providing an overall estimate of the calories burned, they are less accurate when certain activities are measured – like strength training.

Researchers conducted tests on four consumer fitness trackers – Fitbit Flex, Nike+ FuelBand SE, Jawbone UP 24 and Misfit Shine. Their performance were measured for sedentary, aerobic and resistance activity. Though the test was aimed at accuracy of activity trackers, researchers also included two research monitors – the BodyMedia Core and Actigraph GT3X+.

The results were startling. Misfit Shine was the most inaccurate at 30.4 per cent error rate while BodyMedia Core was the top performer with a rate of error of 15.3 percent.

The research was designed to mimic real daily living activities. For the study 56 participants were asked to complete 20 minutes of sedentary activity, such as reading a book, working at the computer or watching a video. That was followed by 25 minutes of their choice of aerobic activity and 25 minutes of resistance exercise, with 5 minutes of rest between each activity.

“By looking at the most commonly performed activities in exercise and daily living settings, we can examine where the errors occur,” said Yang Bai, lead author and a graduate research assistant in kinesiology. “As expected, some monitors overestimate or underestimate all three activities, but some monitors overestimate one type and underestimate the other two categories, which can cancel out if we don’t measure them separately.”

As with the previous activity monitor study, researchers say accuracy is important, but it is only part of the equation in terms of improving physical activity levels.

“I think the key to a consumer is not so much if the activity monitor is accurate in terms of calories, but whether it’s motivational for them and keeps them accountable for activity in a day,” said Greg Welk, professor of kinesiology.

The results are published in Medicine & Science in Sports & Exercise.