Objective: To validate and compare the accuracy of energy expenditure (EE) and step counts measured by ActiGraph accelerometers (ACT) at dominant and nondominant wrist and hip sites. Methods: Thirty young adults (15 females, age 22.93 ± 3.30 years) wore four ActiGraph wGT3X accelerometers while walking and running on a treadmill for 7 min at seven different speeds (1.7, 2.5, 3.4, 4.2, 5.0, 5.5, and 6.0 mph). The EE from each ACT was calculated using the Freedson Adult equation, and the “worn on the wrist” option was selected for the wrist data. Indirect calorimetry and manually counted steps were used as criterion measures. Mean absolute percentage error and two one-sided test procedures for equivalence were used for the analyses. Results: All ACTs underestimated the EE with mean absolute percentage errors over 30% for wrist placement and over 20% for hip placement. The wrist-worn ACTs underestimated the step count with mean absolute percentage errors above 30% for both dominant and nondominant placements. The hip-worn ACTs accurately assessed steps for the whole sample and for women and men (p < .001 to .05 for two one-sided tests procedures), but not at speeds slower than 2.0 mph. Conclusion: Neither hip nor wrist placements assess EE accurately. More algorithms and methods to derive EE estimates from wrist-worn ACTs must be developed and validated. For step counts, both dominant and nondominant hip placements, but not wrist placements, lead to accurate results for both men and women.

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Background: The purpose of this study was to examine the accuracy of heart rate (HR) and energy expenditure (EE) estimated by the Apple Watch Series 1 worn both on the wrist and the upper arm. Methods: Thirty healthy, young adults (15 females) wore the two monitors while participating in a maximal exercise test. Criterion measures were obtained from the Parvo Medics TrueOne 2400 Metabolic Cart and an electrocardiograph. Results: The HR estimations of the arm-worn (AW) Apple Watch had the highest agreement with the electrocardiogram, with mean absolute percent error (MAPE) of <2.5% for the entire sample, for males, and for females, at all exercise intensities. The HR estimations of the wrist-worn Apple Watch had MAPEs ranging from 3.61% (females at very light intensity) to 14.97% (males at very vigorous intensity). When estimating EE for total exercise bout in the entire sample, the arm-worn Apple Watch overestimated EE, with a MAPE of 39.63%, whereas the wrist-worn underestimated EE, with a MAPE of 32.28%. Both the arm- and wrist-worn overestimated EE for females and underestimated EE for males. Conclusion: Wearing the Apple Watch Series 1 on the upper arm versus the wrist improves the MAPE for HR estimations, but does not improve MAPE for the EE calculations when compared to a criterion measure.