Glossary of abbreviations.

<div><p>Introduction</p><p>The ActiGraph (AG) accelerometer is widely used to assess physical activity (PA) in heart failure (HF) patients. However, the validity of the AG in this population remains unexplored.</p><p>Objective</p><p>Therefore, this study examined the criterion validity of the AG-GT9X for measuring step counts (SC) and energy expenditure (EE) among HF patients.</p><p>Methods</p><p>16 patients with HF with preserved ejection fraction (mean age = 60.3±12.1yrs) completed a total of 41 symptom-limited cardiopulmonary exercise tests on a treadmill across multiple time points (median (IQR) = 2.5 (1.5–3.5)). All participants wore the AG (model: GT9X) on both the right ankle and waist locations during the test. Manually counted steps and indirect calorimetry-derived EE served as criterion measures. AG-derived EE was estimated using six different prediction equations previously developed for waist-worn AG. AG-derived measurements were compared with criterion measurements by calculating correlation coefficients, equivalence tests with two one-sided tests, mean absolute percentage error (MAPE), percentage bias, and Bland-Altman plots using mixed models to account for the nested nature of repeated measures within subjects.</p><p>Results</p><p>Ankle-worn AG-SC was significantly equivalent to the criterion (<i>p</i> < .05) and had lower MAPE (<10%) compared to the waist location, regardless of PA intensity level. Sasaki-EE was significantly equivalent to the criterion (<i>p</i> < .05), with the lowest percentage bias overall (0.7%).</p><p>Conclusions</p><p>The ankle-worn AG-SC and Sasaki-EE showed better accuracy among HF patients in laboratory settings. Further research is warranted to cross-validate the results in different settings.</p></div>