ABSTRACT
BACKGROUND: Assessment of percent body fat (%BF) is typically measured with bioelectrical impedance (BIA) as a proxy for dual-energy X-ray absorptiometry (DXA). Notably, poorer agreement between BIA and DXA among persons who are overweight or obese has been reported. The use of electrical impedance myography (EIM) as a proxy for DXA has not been validated. The objective was to evaluate an EIM device and two multi-frequency BIA devices with the reference standard (DXA) stratified by weight status and gender. METHODS: In a convenience sample of 82 adults, %BF assessed by EIM and two BIA devices was compared to DXA. Agreement between devices was tested with intra-class correlation coefficients (ICC) and Bland-Altman plots. RESULTS: Agreement between DXA and EIM (ICC=0.77) was poorer than the agreement between either BIA device with DXA (ICC>0.87). Stratified by sex, agreement between EIM and DXA was greater for men than women (ICC=0.81 and ICC=0.61, respectively). Stratified by BMI, agreement between EIM and DXA was best for normal-weight individuals (ICC=0.89) and progressively poorer for overweight (ICC=0.80) and obese (ICC=0.67) individuals. Bland-Altman plots revealed wide limits of agreement and an increase in EIM mean difference as average %BF increased. Similar trends were seen in BIA assessments. CONCLUSIONS: EIM and BIA substantially underestimate %BF in overweight and obese individuals. Wide limits of agreement coupled with variable ICC limit device interchangeability with one another and limit clinical utility.
Subject(s)
Adiposity , Electric Impedance , Myography/methods , Absorptiometry, Photon , Adipose Tissue , Adolescent , Adult , Aged , Aged, 80 and over , Body Mass Index , Female , Humans , Male , Middle Aged , Obesity , Overweight , Young AdultABSTRACT
OBJECTIVES: Inexpensive activity monitors have recently gained popularity with the general public. Researchers have evaluated these consumer-based monitors in laboratory-conditions. Given the current wide-spread consumer use of these devices, it is important to ensure users are attaining accurate information compared to previously validated measures. This study investigates the accuracy of Fitbit One and Flex activity monitors in measuring steps, sedentary time, and time spent in light, moderate, and vigorous intensity activities with ActiGraph GT3X+ with female adults in free-living conditions. DESIGN: Cross-sectional study. METHODS: Twenty-two women, 21.23±1.63 years, BMI: 22.35±2.34kg/m2 wore two Fitbit Ones (bra and waist), one Fitbit Flex on the wrist, and one ActiGraph GT3X+ on the waist for seven-consecutive days. Repeated measures ANOVA was used to explore differences in steps, sedentary time, and time spent in light, moderate and vigorous intensity activities among the four devices. RESULTS: No differences were found in number of steps recorded across the four devices. Fitbit One, waist and bra, overestimated time spent in light intensity activities. Fitbit One (waist) and Fitbit Flex overestimated time spent in moderate intensity activities. Fitbit One, waist and bra, and Fitbit Flex overestimated time spent in vigorous intensity activities. All Fitbit activity monitors overestimated MVPA and underestimated sedentary time compared to the ActiGraph. CONCLUSIONS: Regardless of wear-location all Fitbit devices provide similar activity monitoring and users can wear the devices wherever best accommodates their lifestyle or needs. Users should not rely solely on these monitors when tracking vigorous and MVPA activities.
