This document discusses heart rate and how to monitor it. It defines key heart rate metrics like resting heart rate, maximum heart rate, and heart rate reserve. It explains that maximum heart rate declines with age and can be estimated using the formula 220 - age. Heart rate reserve is the difference between maximum and resting heart rate. The document also discusses aerobic training heart rate zones for fat burning, noting that burning fat most efficiently occurs between 50-75% of one's heart rate reserve. Formulas and examples are provided to calculate these various heart rate values.