科学美国人60秒 健身手环计算的卡路里不准（在线收听）

Fitness bands like the Apple Watch and the Fitbit aim to track your vitals, like heart rate. But early models weren't all that accurate."We thought of them a little bit like random number generators. They really didn't seem to be providing anything that bore any relationship to heart rate." Euan Ashley, a cardiologist who studies wearables at Stanford University.

像苹果手表和Fitbit这样的健身手环其设计初衷是追踪人的重要生命指数，比如心率。但是它们的早期版本却并没有那么精确。“我们认为它们有点像随机数生成器。它们似乎并未提供任何与心率有关的数据信息。”斯坦福大学研究可穿戴设备的心脏病专家尤安·阿什利说道。

He and his colleagues have now tested seven newer fitness bands—from brands like Apple, Fitbit and others—and he says those heart rate stats have gotten way better. "Yeah we were pleasantly surprised actually by how good the accuracy of the heart rate monitoring was."

目前他和同事们已测试过7种分别来自苹果、Fitbit和其他品牌的较新型的健身手环。他表示，那些心率数据统计已经变得好多了。“是的，我们惊喜地发现心率监测的准确性确实已经很好了。”

For most of the devices, the error rate was less than five percent—good enough for your doctor. But where all the devices failed to measure up was estimating calories burned. Even the most accurate devices were off by 27 percent, compared to lab measurements of energy expenditure. One device was off by more than 90 percent.

大多数设备的错误率小于5%——这对您的医生来说已经足够好了。但是，所有设备对卡路里的消耗评估都未合格。就连最准确的设备与实验室测量的能量消耗率相比也差了27%。其中一个设备甚至相差了90%多。

"If you think about going to the gym and working out for an hour and maybe that's around 400 calories, in reality that could be anything from 200 to 800. And that's a big difference if you're thinking about somebody who's incorporating those estimates into their lifestyle and thinking about what to eat that evening based on the workout they did that afternoon." The results are in the Journal of Personalized Medicine.

“如果你考虑去健身房锻炼一个小时，或许能消耗大约400卡路里，然而实际的消耗指数有可能是200到800之间的任何值。如果你把这一数据用于那些将其融入生活方式当中，并以当天下午的锻炼为基准来衡量当晚进食哪些晚餐的人，那意义就大有区别了。“该研究结果发表在《个性化医学》杂志上。”

The reason for the discrepancy, Ashley says, could be that we all burn energy at different rates—and that's hard to reckon from simple input stats like weight and height. "Some people are incredibly efficient and look incredibly elegant when they run. And others really clearly look like they're burning a lot more calories to cover the same amount of ground." So if you own a wearable, it's probably safe to trust the heart data. What it can't tell you is whether your time on the treadmill really justifies that chocolate shake.

阿什利表示，造成这种差异的原因可能是我们消耗能量的速率不同，而且这很难从简单的体重和身高等输入数据中估算出来。“有些人跑步时非常高效，而且看起来非常优雅。而另一些人跑同样的路程，则看起来明显需要燃烧更多的卡路里。”因此，如果你拥有一个可穿戴设备，相信它的心率数据可能比较安全。但它无法告诉你的是——你在跑步机上跑步的时间是否真的能消耗掉那杯巧克力奶昔。