FORGET Fitbits, Fuelbands and other pedometers. Your smartphone and its built-in sensors can do a better job of measuring the energy you expend during the day.
Amit Pande of the University of California, Davis, designed an activity tracking algorithm for smartphones. It works by training a neural network, which functions like a simplified human brain, to recognise features in the data gathered by the phone's accelerometer and barometer. The system also takes account of variables like age, gender, height and weight to estimate energy expenditure.
The team compared their system to the Fitbit and Nike's Fuelband, the leading activity monitors on the market, as well as a professional, wearable calorimeter. It was more accurate than the commercial devices and closely matched the calorimeter.
Fitbit and Fuelband tested particularly badly on stairs. In trial runs up and down four flights of stairs, the commercial devices estimated that more energy was expended going down than up – clearly untrue. In contrast, the smartphone performed better thanks to its barometer, which measures the tiny changes in atmospheric pressure that tell the device when someone is going up and down stairs.
"This is a new market, so in the beginning people are not so worried about accuracy," Pande says. "But we want accurate data so that physicians can use it to improve their understanding of human beings."
Pande and colleagues will demonstrate the system at the Wireless Health conference in Baltimore this week.
Pande is not alone in taking the smartphone-only approach to monitoring human activity. Health data start-up Ginger.io also relies on activity traces from your smartphone's sensors, as well as your text and phone activity, to make predictive health insights and alerts.
Mike Brown of the National University of Singapore says he is impressed with Pande's work, but notes that there are some obvious downsides to phone-only activity sensing. "iPhones and Androids need to charge at least once a day. Fitbit and Nike Fuelband can work for seven to nine days on a single charge," he says." And ever try to run a marathon carrying a phone?"
This article appeared in print under the headline "Ditch the Fitbit – track fitness with your phone"
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