ECG-based Indices of Physical Activity

George B. Moody
Harvard-M.I.T. Division of Health Sciences and Technology, Cambridge, MA, USA

This article originally appeared in Computers in Cardiology 1992, vol. 19, pp. 403-406 (IEEE Computer Society Press). Please cite this publication when referencing this material. A sample implementation of the algorithm described in this paper is available in source form here.

Abstract:

Inter-subject comparisons of heart rate variability (HRV) require that physical activity levels be matched between subjects, to minimize the confounding effects of intra-subject variability in HRV measurements. HRV studies based on standard ECG recordings are hindered by these effects. The current study investigated methods for finding periods of minimum physical activity based on the ECG alone. This paper describes an ``activity index'' (based on mean heart rate, total power of the observed heart rate signal, and a heart rate ``stationarity 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.