Today I tapped into the techno-geek knowledge of my colleague, Amanda Zaleski, M.S., who wrote this guest post on the latest and greatest in physical activity monitors.
Yesterday, as I stood there with my clipboard and heart rate monitor supervising a patient on the elliptical, I pondered how funny this scenario would look to a caveman. The human body was designed to hunt and gather and through that peak physical fitness was inherently achieved. We did not require equipment, trainers, or gym memberships. We just… did it! The use of technology to motivate and measure planned physical activity today is thus somewhat ironic as one might argue that technology is the antithesis of exercise. In any event, we live in a digital world and our dependence on fitness tracking apps and social media feedback is unavoidable, so how do we know which product is the best? Well, I’ve done the work for you. A recent article in the New York Times comparing various physical activity monitors piqued my interest enough to do a mini-review on the top three wrist accelerometer products used for physical activity determinations.
Fitbit Flex. The Fitbit Flex is a three dimensional accelerometer worn on the wrist that can track steps, distance, calories burned, stairs climbed and sleep.
Pros: Relatively small. Waterproof. Can be worn 24-7. Mobile tools allow food, goals and trends to be logged and tracked. Syncs wirelessly (no plugging in). Able to interact and share with friends. Positive Feedback. Syncs with other fitness/health apps. Has an altimeter (tracks heights/stairs). Good online community support.
Cons: The screen isn’t readable so the user has to log in several times a day if they want an exact quantification of their expenditure. Does not track any movement that doesn’t involve the wrist (ie, stationary bike, yoga, etc)
Validity: In a recent study conducted at the University of Colorado, researchers found that energy expenditure was underestimated by as much as 28%. When activities were labeled, this variance was reduced to 12%; however, this requires a significant investment of time.
Mobile Compatibility: iPhone or Android
Price: $99.95 (with an optional $49 to download the data off the website)
Nike+ Fuel Band. Similar to the Fitbit, the Nike+ Fuel Band is also a three dimensional accelerometer bracelet that tracks steps, distance, calories burned and goals. The Nike+ Fuel Band also has a social media component, in that it allows you to share your activity and connect with friends.
Pros: Fashionable. Nice graphic display. Wirelessly syncs (to phone) or USB to computer. Doubles as watch (time display). “Fuel points” are assigned to each activity based on intensity of accelerometer data and oxygen kinetics. Mass online community and support.
Cons: Water resistant, but not water proof. Cannot be worn 24/7. Only syncs with iOS5+. Also, does not track any movement that doesn’t involve the wrist. Does not include altimeter.
Validity: To the best of my knowledge, there are no studies that have examined energy expenditure data, however, anecdotally our lab has found that accelerometers have a hard time distinguishing between vigorous and moderate activity and moderate and light activity, therefore, I would be interested to see the algorithms that compute intensity and assign respective fuel points. It seems plausible that the use of fuel points introduce a whole different (and unnecessary) source of potential variability.
Mobile Compatibility: iPhone or iPad
Jawbone Up. The Jawbone Up is also a three dimensional accelerometer bracelet that tracks steps, distance, calories burned, sleep, and mood.
Pros: Fashionable. Lots of colors available. Small. Wirelessly syncs (to phone) or USB to computer. Long battery life (10 days). Tracks mood, caloric intake and sleep. Contains a motor that vibrates if sedentary for too long (haptic feedback). Syncs with other health and fitness apps.
Cons: Water resistant, but not water proof. No visual display or feedback (unless you log in). Also, does not track any movement that doesn’t involve the wrist. There is no online community to share results, however, you may post results with shared or invited friends. No wireless sync.
Validity: To the best of my knowledge, there are no studies.
Mobile Compatibility: iPhone or Android
In summary, the science to back up the validity and accuracy of these three products is lacking. A Pubmed search only yielded one study performed on these outcome variables (Fitbit Flex) and found that energy expenditure was underestimated by almost 30%. Anecdotally, there are various online forums and product reviews that consistently site all three products to have classification inaccuracies (i.e., poor discrimination between walking and running). Furthermore, because the accelerometer is worn on the wrist, any excessive wrist movement (jostling, driving, waving, etc.) is misidentified as whole body activity and results in overestimation energy expenditure. Conversely, any activity that does not involve arm motion is under-reported. If I had to weigh all of the information and recommend one of these products to a family member, it would be the Fitbit Flex. It simply has the most personal metrics, including an altimeter and sleep detection/analysis. It is able to track calories and goals and share them with friends and an online community. The visual display provides graphical feedback (a flower wilting with low activity, which blossoms with increases in activity) as well as quantitative analysis. Although you have to log in to a computer or phone to see your data, I don’t see this as a huge issue because I use my phone constantly anyway. Also, this is the only product of the three that is waterproof allowing all water sports to be tracked instead of having to manually enter the type, time and intensity (leaving a lot of room for error). It also works well with other apps, syncs wirelessly AND is the least expensive!