ECG-based indices of physical activity

Inter-subject comparisons of heart rate variability (HRV) require that physical activity levels be matched between subjects, to minimize the confounding effects of intrasubject variability in HRV measurements. The current study investigated methods for finding periods of minimum physical activity based on the electrocardiogram (ECG) alone. The author describes an activity index based on the heart rate, total power of the observed heart rate signal, and a heart rate stationary index, and presents an algorithm for locating periods of minimum activity by tracking this activity index. The algorithm was tested using a set of 35 ECG recordings for which an independent activity indicator was available. The algorithm consistently selected periods of minimum activity in agreement with the independent activity indicator. No discrepancies were noted in any of the 35 cases