Knowing your heart rate when you're exercising is important. The formula for determining your target heart rate is 220 minus your age. That number is your maximum heart rate, The American College of Sports Medicine recommends 30 to 60 minutes of aerobic exercise 3 to 5 days a week at 60-80% of your maximum heart rate. To calculate this, take 220 minus your age and then multiply that number times.6 for 60%, .7 for 70% or .8 for 80% of your maximum heart rate. So, if you are 50,
220-50=170. 170 x .7=119 which is 70% of your maximum heart rate. Many of the aerobic machines have heart rate monitors built in that will tell you your heart rate. Exercising at 60 to 70% of your maximum heart rate teaches your heart to pump blood more efficiently. Your heart is a muscle and it responds to exercise the same way other muscles do--by getting bigger and stronger.