University of Delaware, Department of Behavioral Health and Nutrition, Newark, DE, United States.
JMIR Mhealth Uhealth. 2016 Sep 19;4(3):e110. doi: 10.2196/mhealth.6281.
Wearable activity monitors such as Fitbit enable users to track various attributes of their physical activity (PA) over time and have the potential to be used in research to promote and measure PA behavior. However, the measurement accuracy of Fitbit in absolute free-living conditions is largely unknown.
To examine the measurement congruence between Fitbit Flex and ActiGraph GT3X for quantifying steps, metabolic equivalent tasks (METs), and proportion of time in sedentary activity and light-, moderate-, and vigorous-intensity PA in healthy adults in free-living conditions.
A convenience sample of 19 participants (4 men and 15 women), aged 18-37 years, concurrently wore the Fitbit Flex (wrist) and ActiGraph GT3X (waist) for 1- or 2-week observation periods (n=3 and n=16, respectively) that included self-reported bouts of daily exercise. Data were examined for daily activity, averaged over 14 days and for minutes of reported exercise. Average day-level data included steps, METs, and proportion of time in different intensity levels. Minute-level data included steps, METs, and mean intensity score (0 = sedentary, 3 = vigorous) for overall reported exercise bouts (N=120) and by exercise type (walking, n=16; run or sports, n=44; cardio machine, n=20).
Measures of steps were similar between devices for average day- and minute-level observations (all P values > .05). Fitbit significantly overestimated METs for average daily activity, for overall minutes of reported exercise bouts, and for walking and run or sports exercises (mean difference 0.70, 1.80, 3.16, and 2.00 METs, respectively; all P values < .001). For average daily activity, Fitbit significantly underestimated the proportion of time in sedentary and light intensity by 20% and 34%, respectively, and overestimated time by 3% in both moderate and vigorous intensity (all P values < .001). Mean intensity scores were not different for overall minutes of exercise or for run or sports and cardio-machine exercises (all P values > .05).
Fitbit Flex provides accurate measures of steps for daily activity and minutes of reported exercise, regardless of exercise type. Although the proportion of time in different intensity levels varied between devices, examining the mean intensity score for minute-level bouts across different exercise types enabled interdevice comparisons that revealed similar measures of exercise intensity. Fitbit Flex is shown to have measurement limitations that may affect its potential utility and validity for measuring PA attributes in free-living conditions.
可穿戴活动监测器（如 Fitbit）使使用者能够随时间跟踪其身体活动（PA）的各种属性，并且有可能在研究中用于促进和衡量 PA 行为。然而，Fitbit 在绝对自由生活条件下的测量精度在很大程度上是未知的。
在自由生活条件下，检查 Fitbit Flex 和 ActiGraph GT3X 对量化步数、代谢当量任务（MET）以及久坐活动和轻、中、高强度 PA 的时间比例的测量一致性，在健康成年人中。
一个方便的样本由 19 名参与者（4 名男性和 15 名女性）组成，年龄在 18-37 岁之间，分别佩戴 Fitbit Flex（手腕）和 ActiGraph GT3X（腰部）1 或 2 周的观察期（分别为 n=3 和 n=16），其中包括自我报告的每日运动。检查日常活动数据，平均 14 天，报告运动的分钟数。平均每日数据包括步数、MET 和不同强度水平的时间比例。分钟级数据包括用于整个报告运动的步数、MET 和平均强度分数（0=久坐，3=剧烈）（N=120）和按运动类型（步行，n=16；跑步或运动，n=44；有氧运动机，n=20）。
在平均日常和分钟观察中，设备之间的步数测量值相似（所有 P 值>.05）。Fitbit 显著高估了平均日常活动的 MET，报告的运动总分钟数，以及步行和跑步或运动（平均差异 0.70、1.80、3.16 和 2.00 MET，分别；所有 P 值<.001）。对于平均日常活动，Fitbit 分别低估了久坐和低强度的时间比例 20%和 34%，并高估了中高强度的时间比例 3%（所有 P 值<.001）。不同运动类型的总运动分钟数或跑步或运动和有氧运动机的平均强度分数无差异（所有 P 值>.05）。
Fitbit Flex 为日常活动和报告的运动分钟数提供了准确的测量值，无论运动类型如何。尽管不同设备之间的不同强度水平的时间比例不同，但检查不同运动类型的分钟级运动的平均强度分数可以进行设备间比较，揭示出类似的运动强度测量值。Fitbit Flex 显示出测量限制，这可能会影响其在自由生活条件下测量 PA 属性的潜在实用性和有效性。
