Fitness Trackers: Wrong Calorie Counts
The good news about your fitness tracker is that it probably gets your heart rate right. However, new research reveals that most are way off when counting calories. Researchers at Stanford University tested seven trackers to see whether or not you can trust the information they provide. The team recruited 31 women and 29 men to wear the devices while walking or running on treadmills or riding stationary bikes. The volunteers’ heart rate was measured with a medical grade electrocardiogram (EKG) and the calories expended were “counted” with an instrument used in physiology research to estimate metabolic rate. The researchers reported that six of the devices were less than five percent off in their measurements of heart rate when compared to the EKG results. But none of the devices came close to accurately counting calories burned. The most accurate device was off by an average of 27 percent while the least accurate was off by 93 percent. The study also revealed that tracker errors were higher for study participants with darker skin, higher BMIs and men than for white women with a more healthy weight. The researchers noted that tracker accuracy should ideally be within 10 percent of results from medical-grade devices.
My take? In my view, the key question raised by the use of fitness trackers is whether they actually motivate you to be more active. The accuracy of the information they provide becomes more important for those who rely on it for making adjustments to their exercise routines or diet. The results of the Stanford study suggest that you shouldn’t rely on today’s trackers for an accurate accounting of the calories you expend while wearing one. I think these devices are worthwhile if they actually inspire you to become more active, and I assume they’ll become more sophisticated and accurate over time. However, for many people, teaming up with one or more human beings, rather than an electronic device, remains the most reliable way to boost motivation to exercise.
Euan Ashley et al, “Accuracy in Wrist-Worn, Sensor-Based Measurements of Heart Rate and Energy Expenditure in a Diverse Cohort.” Journal of Personalized Medicine, May 24, 2017, doi: 10.3390/jpm7020003
Also in this week’s bulletin:
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