Revisiting the measurement of cardiovascular exercise: comparing AZMs and Cardio Load

Wearable heart rate monitors have transformed how we monitor exercise's impact on the
cardiovascular system, moving from coarse classification to precise measurement. Metrics
such as Google Fitbit’s Active Zone Minutes (AZMs) guide users in assessing their exercise

volume and intensity relative to global physical activity guidelines. These help optimize health
but are less sensitive to the small changes needed to optimize performance. To complement
AZMs, a new performance-oriented metric, Cardio Load, has been introduced to quantify
cardiovascular exertion across the full spectrum of activity intensity. By incorporating light
activity and exponentially weighting higher intensities, Cardio Load provides a more nuanced
and personalized understanding of exercise impact for those exercising regularly. This allows
individuals to optimize their workouts for both health and performance goals, ensuring
appropriate workload management and recovery. This paper explores the theoretical basis for
Cardio Load and its practical applications.