Introduction: Accelerometers are used to quantify energy expenditure in field research. The ActiGraph™ GT1M (ActiGraph™) is a commonly used accelerometer for research. The FitBit ® Ultra (FitBit ®) is a low-cost alternative to the ActiGraph™; however, there is limited research on the validity of this device. Purpose: The pilot study compares the FitBit ® against the ActiGraph™ and metabolic cart for measurement of energy expenditure and step counts during treadmill walking. Methods: Thirty-two (25 female) adults, mean age 22±2 years, performed two thirty-minute phases of walking (slow and brisk) on a treadmill while concurrently wearing the FitBit ® and the ActiGraph™. Energy expenditure estimates were compared against energy expenditure measured by a metabolic cart. The Pearson's correlation and t-tests determine the linear association and similarity between the accelerometers. Results: Energy expenditure estimate is moderately correlated between the two accelerometers during slow walking (r=0.584, p=0.011) and strongly correlated during brisk walking (r=0.910, p<0.001). Step count is strongly correlated between the accelerometers during slow (r=0.974, p<0.001) and brisk (r=0.996, p<0.001) walking. The FitBit ® significantly underestimated energy expenditure during brisk walking compared to metabolic cart data. There is no difference between the slow and brisk phases' step counts using either accelerometer. Conclusion: The results of this pilot study suggest that the FitBit ® and the ActiGraph™ can be used interchangeably to measure steps, but not to measure kilocalories. Furthermore, the FitBit ® underestimates energy expenditure, compared to a metabolic cart, as exercise intensity increases. This limits its ability to accurately measure energy expenditure in active populations.

Purpose Immediately following reactive hyperemia, the arteries in some individuals constrict before they begin to dilate. We have defined this physiological response high flow-mediated constriction (H-FMC). The aim of this study was to describe the frequency of the H-FMC during reactive hyperemia in children and adolescents throughout a range of body mass index (BMI) values and investigate differences in flow-mediated dilation (FMD), cardiovascular, and anthropometric measures between those subjects who experience this phenomenon and those who do not. Methods FMD was assessed in 136 children and adolescents (61 male, 75 female; 13±3 years) by ultrasound imaging the brachial artery. H-FMC was characterized as the lowest point from the baseline brachial artery diameter immediately following reactive hyperemia cuff release. Independent t-tests were used to compare differences between subjects who demonstrated an H-FMC vs. Non-H-FMC. Results H-FMC was observed in 91 of the 136 participants (66.9%). No significant difference was found between H-FMC vs. Non-H-FMC subjects for age (P=0.602), gender (P=0.767), height (P=0.227) or weight (P=0.171). BMI percentile was trending toward significance in H-FMC vs. Non-H-FMC individuals (91.8th±14.9thvs.84.6th±22.8th percentile, P=0.057). FMD was significantly lower in H-FMC vs. Non-H-FMC subjects (5.43±3.41vs.8.05±3.97%, P<0.001). If the H-FMC was added to the FMD there was no significant difference in dilation between H-FMC and Non-H-FMC individuals (8.03±3.27%vs.8.05±3.97%, P=0.977). Conclusion Approximately 67% of participants demonstrated the high flow-mediated constriction during reactive hyperemia with BMI percentile being higher and FMD lower in children and adolescents who displayed this phenomenon.

The accuracy of an infrared three-dimensional (3D) body scanner in determining body composition was compared against hydrostatic weighing (HW), bioelectrical impedance analysis (BIA), and anthropometry. A total of 265 adults (119 males; age = 22.1 ± 2.5 years; body mass index = 24.5 ± 3.9 kg/m) had their body fat percent (BF%) estimated from 3D scanning, HW, BIA, skinfolds, and girths. A repeated measures analysis of variance (ANOVA) indicated significant differences among methods (p < 0.001). Multivariate ANOVA indicated a significant main effect of sex and method (p < 0.001), with a non-significant interaction (p = 0.101). Bonferroni post-hoc comparisons identified that BF% from 3D scanning (18.1 ± 7.8%) was significantly less than HW (22.8 ± 8.5%, p < 0.001), BIA (20.1 ± 9.1%, p < 0.001), skinfolds (19.7 ± 9.7%, p < 0.001), and girths (21.2 ± 10.4%, p < 0.001). The 3D scanner decreased in precision with increasing adiposity, potentially resulting from inconsistences in the 3D scanner's analysis algorithm. A correction factor within the algorithm is required before infrared 3D scanning can be considered valid in measuring BF%.

We found no difference in FMD regardless of the baseline brachial artery diameter used in children and adults. Therefore, compilation of data and comparison of results from studies utilizing different measures of baseline brachial diameter may be able to be conducted.

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