August 06, 2013
Accelerometers are devices that record motion that are quickly gaining popularity in the world of health promotion and fitness. These small sensors can easily be attached to your wrist or hip and are being used to monitor the amount of physical activity you do throughout your day. A new device that fits in your shoe is being tested at Colorado State University.
How accurate are today's physical activity monitors? To put it simply: there is room for improvement.
Ray Browning, an assistant professor in the Department of Health and Exercise Science at Colorado State University, and his colleagues are currently involved in ongoing research to try to improve objective measures of physical activity using simple, unobtrusive monitoring devices. Browning, who runs the Physical Activity Lab, has helped evaluate current accelerometers on the market, as well as worked on a prototype for an accelerometer/pressure sensor worn in the shoe.
"We use accelerometry to measure physical activity, and right now we're spending a lot of time trying to better understand that tool as a measure," said Chrissy Schaefer, a third year human bioenergetics Ph.D. student in the Physical Activity Lab.
In a recently published research study, A Comparison of Energy Expenditure Estimation of Several Physical Activity Monitors, Browning and his team tested the accuracy of research and consumer monitoring devices that use accelerometers, as well as a footwear-based physical activity monitor of their own creation.
"We have several research projects that are going on around activity monitoring in general," Browning said. "Both developing new techniques to monitor activity as well as using existing commercially available accelerometers that researchers and/or consumers can buy to track activity and estimate energy expenditure."
Through collaboration with the Health Sciences Center at the University of Colorado Denver, Browning's research team had ten male and nine female healthy adults complete a four-hour stay in a room calorimeter. A room calorimeter is an air-tight room that measures how much oxygen a person is consuming and carbon dioxide they're producing while they're in the room. "Those two things can give us an estimate of how much energy you're expending, or how many calories you're burning," Browning said.
Each of the participants wore a shoe with multiple sensors that was developed by SmartMove, a local start-up company created to commercialize the shoe-based device. In addition, participants wore research and consumer monitors including the Actical, DirectLife, and Fitbit devices, while performing a series of postures and activities like sitting, standing, running on a treadmill, and riding a bike. While completing these every day activities with different devices on their wrists, waist, and shoes, they were then able to compare the estimation of energy expenditure from those monitoring devices against one key measure: how many calories participants actually burned in that room.
"For the most part," Browning said, "the device we're working on and one other device were accurate, but the rest of them are not. We also tried devices that you could buy as a consumer, but the FitBit device, for example, turned out to not provide a very accurate measure of energy expenditure."
Browning said this study confirms peoples' hypothesis that these relatively simple sensors and accelerometers that claim to be able to measure all of your physical activity with one sensor on one part of your body are generally not very accurate, though the area of physical activity monitoring in general is a rapidly evolving area, as is evidenced by Browning and his team's own invention.
The SmartMove device is an insole with two very thin pressure sensors built into it, combined with an accelerometer, so there are multiple sensors on the foot that all can communicate wirelessly with a smartphone.
"That device actually is quite accurate in estimating energy expenditure," Browning said. "Part of the reason why is that it can estimate what you're doing, such as walking, sitting, standing, riding a bicycle, or walking up stairs, and there is an associated energy expenditure with each of those tasks. By being able to classify the activity, we are better able to estimate the energy expenditure."
Browning's research found that single accelerometer based devices may underestimate the amount of energy you are expending, especially during some tasks. For example, when carrying a heavy backpack a wrist mounted accelerometer is unable to detect the additional load. Hip-mounted accelerometers also often don't accurately estimate energy expenditure when you're riding a bicycle; the device associates the detected motion as similar to sitting.
Browning said these devices probably aren't yet ready for you to rely on for accurate estimates of energy expenditure, and as a result should not be used to plan your diet, but they still can be a great way to measure significant changes in physical activity.
The constant challenge is that everybody is different and moves differently, and even if a measurement device looks really good in a lab, it doesn't necessarily mean it's going to be completely accurate in daily life. While difficult, every problem Browning and his team help get closer to solving will ideally benefit researchers and health professionals around the world.
"We're able to work on devices that hopefully will not only help consumers live healthier lives," Browning said, "but also help researchers design better interventions and programs to change physical activity based on objective measures of activity."
To view more photos of the Physical Activity Lab, visit our Flickr page.
Photo: Ray Browning, assistant professor, right, and Wayne Board, research associate in the Physical Activity Lab, demonstrate the shoe insole sensor which sends data to an iPhone.
The Department of Health and Exercise Science is part of the College of Health and Human Sciences at Colorado State University.
Contact: Gretchen Gerding