Calculating your EBZ is an easy and fairly accurate way of determining your exercise intensity. Monitoring exercise intensity is important to achieving optimal aerobic condition. You can calculate your EBZ, sometimes called Target Heart Rate (THR), by using the formula (in red) in the graphic above, or by using the chart on the right. Calculate for the upper (85%) and lower (70%) limits. These limits represent the highest and lowest heart rates necessary to achieve optimal aerobic fitness. The next time you go out to perform aerobic exercise, about 10 minutes into your workout, slow down to take your heart rate. Your heart rate for 15 seconds should be between the 70-85% range.