220 - 23 = 197 bpm
Aerobic Zone (Endurance Training) --- 70 - 80% of maximum heart rate: 137.9 - 157.6 bpm
The aerobic zone will improve your cardiovascular and respiratory system AND increase the size and strength of your heart. This is the preferred zone if you are training for an endurance event. More calories are burned with 50% from fat.
Anaerobic Zone (Performance Training) --- 80 - 90% of maximum heart rate: 137.9 - 177.3
Benefits of this zone include an improved VO2 maximum (the highest amount of oxygen one can consume during exercise) and thus an improved cardiorespiratory system, and a higher lactate tolerance ability, which means your endurance will improve and you'll be able to fight fatigue better. This is a high intensity zone burning more calories, 15 % from fat.
A heart rate monitor simply monitors the rate of your heart and provides feedback. Although they are not always precise, they generally work well enough to give you an approximation of your heart rate as you exercise. By using a heart rate monitor you can ascertain a exercise level that will optimize the burning of fat and you will improve your metabolism.
If you are beginning an exercise regimen over exercising and raising your heart level too high can be counterproductive. You can exert yourself beyond an aerobic workout. When your heart exceeds 85% you are in an anaerobic zone. This is when your body burns less fat and more carbohydrates. In the process you produce lactic acids. A heart rate monitor assists you in staying in the preferably aerobic zone.
source: http://www.ellipticaltrainers.com/info/heart_monitor.htm
