The Stanford researchers examined measurements recorded when people were at rest and while they exercised.
"People are basing life decisions on the data provided by these devices," said Euan Ashley, one of the study investigators.
The study looked at seven fitness trackers worn on the wrist:
They were Apple Watch, Basis Peak (version 1), Fitbit Surge and Microsoft Band (version 1). The others three were Mio Alpha 2, PulseOn, and Samsung Gear S2.
其中包括Apple Watch，Basis Peak（version 1），Fitbit Surge和Microsoft Band (version 1)，另外还包括Mio Alpha 2，PulseOn和Samsung Gear S2。（51VOA注：以上为各公司出品的智能手表或手环）
Sixty participants of both sexes wore up to four trackers on their wrists as they sat, and as they exercised on a treadmill and a stationary bike. The participants were a mix of sizes and fitness levels.
The trackers measured the heart rates and energy used, or calorie burn, in activities from sitting to a slow walk to a run. They also tested people cycling at different speeds.
Professional medical instruments measured participants' heart and breathing rates as well as temperature and blood pressure. The researchers compared the fitness tracker measurements to those of the "gold standard medical instruments."
The final report on the study was published last week. It found that none of the trackers met what researchers considered an acceptable error rate for energy use measurement. The acceptable error rate is five percent or less.
The researchers wrote that the Fitbit Surge was the most accurate tracker of energy use. It had a 27.4 percent average error rate. The study found the PulseOn to be the least accurate tracker, with a 92.6 percent error rate.
The error rate was higher for males than for females with all fitness trackers tested. The average error rate for all the trackers studied under all forms of exercise was four percent higher for males than for females.
The good news is the tested fitness trackers were accurate at measuring heart rate. All but one of the trackers met the acceptable error rate limit in heart rate measurement.
Of the trackers studied, the Apple Watch was the most accurate at measuring heart rate, with an average error rate of two percent. The Samsung Gear S2 was the least accurate with an average error rate of close to seven percent.
在这些追踪器中，Apple Watch在测量心率方面是最准确的，平均误差率是2%。Samsung Gear S2在测量心率方面是最不准确的，平均误差率接近7%。
For both the measurement of energy used and heart rate, the researchers said "the Apple Watch had the most favorable error profile while the Samsung Gear S2 had the least."
研究人员表示，对能量消耗和心率两种测量来说，Apple Watch拥有最有利的误差文档，而Samsung Gear S2最不利。
The Stanford researchers are continuing their investigation of fitness trackers. Next, they will test participants wearing fitness trackers during their daily lives and while exercising outside a laboratory.
The full study is available online at The Journal of Personalized Medicine.
I'm Caty Weaver.