What does the term "heart rate reserve" refer to in the context of the Karvonen formula?

The term "heart rate reserve" is defined as the difference between an individual's maximum heart rate and their resting heart rate. This measure is essential in the context of the Karvonen formula, which is utilized to determine target exercise heart rates.

To calculate heart rate reserve, one first needs to establish the maximum heart rate, generally calculated using the formula 220 minus the person's age. From this value, the resting heart rate—ideally measured after a period of rest, such as first thing in the morning—is subtracted. This calculation helps in identifying the heart rate range that an individual can safely work within during exercise to improve cardiovascular fitness while considering both the resting and active states of the heart.

This understanding is central to designing personalized exercise programs that effectively elevate a person's heart rate to target intensities for cardiovascular benefits without overexertion.