“…In 1991, we developed a new technique for simultaneous monitoring of the electrocardiogram (ECG) and walking stride rate in order to study the relationship between ECG changes (e.g., arrhythmias, ischemia, mean heart rate, and heart rate variability) and physical activity (e.g., supine, standing, walking, and walking rate) on a beat-by-beat and stride-by-stride basis (Hausdorff, Forman, Pilgrim, Rigney, & Wei 1992). Many investigations had shown that measures of heart rate dynamics and heart rate variability, an indicator of cardiovascular health, are sensitive to alterations in the autonomic nervous system's regulation of heart rate (Goldberger et al, 2002;Ho et al, 1997;Lipsitz, Mietus, Moody, & Goldberger, 1990;Peng et al, 1993). Indeed, one could suggest that the study of heart rate dynamics has turned into a discipline of its own, with literally thousands of research article s on this topic spanning those that have examined the basis for healthy heart rate dynamics to those that have examined clinical utility of measures based on heart rate dynamics.…”