This paper describes the Ambulatory Monitoring System (AMS) for measuring and scoring heart rate, heart rate variability, and the amount of body movement during normal daily activities. After a technical description of the system, results from a validation study are presented in which heart rate and heart rate variability measured with the AMS showed predictable variation with time of day, posture, physical activity and the type of activity that the subjects were engaged in. It is con-cluded that the Ambulatory Monitoring System is a valid system for non-invasive real-life monitoring of heart rate and heart rate variability.

We examined the effect of training state on cardiac autonomic control in a naturalistic setting. Twenty-four vigorous exercisers were compared to age-and sex-matched sedentary controls. The regular exercisers were subjected to a 6-week training program after which they were randomized to 2 weeks of continued training or 2 weeks of detraining. Cardiac autonomic control was measured over a 24-h period by ambulatory recording, using the preejection period (PEP) and respiratory sinus arrhythmia (RSA). Nonexercising controls had a significantly higher ambulatory heart rate (HR) compared to the regular exercisers but comparable 24-h levels of PEP and RSA. In regular exercisers, 2 weeks of detraining did not significantly change the 24-h levels of HR, PEP, or RSA. We conclude that the bradycardia in healthy regular exercisers is the result of a lower intrinsic heart rate rather than a shift in cardiac autonomic balance from sympathetic to vagal control.