Phrase C from the list.
Intensity for exercise is often measured by the percentage of your maximum heart rate that is achieved during the workout.
This method involves determining your maximum heart rate (usually estimated as 220 minus your age) and then aiming to reach a certain percentage of that maximum during your exercise session. For example, exercising at 70-85% of your maximum heart rate is typically considered moderate to high intensity. This measure provides a quantifiable way to gauge the effort level of your workout and ensure that you are challenging yourself appropriately for your fitness goals.
