To get the most from HRT, you need to know the zones and what they can do for you. You first need to know your HRmax. Once you know this number all you need to do is multiply it by the percentages listed to get the Heart Rate Zone that you are aiming for .(to figure out HRmax see post "know your zone", 5/7/07, label-exercise)
Zone #1: Warm-up Zone (50-60% of HRmax) This can also be used as a cool down or recovery zone. This is an easy and comfortable zone. Use it to warm up the muscles and joints and get the blood pumping.
Zone #2: Moderate Aerobic Zone (60-70% of HRmax) This zone represents an intensity level that promotes good calorie burning, two-thirds of the calories burned are from fat.
Zone #3: Intense Aerobic Zone (70-80% of HRmax) In this zone you are burning about 50% carbohydrates and 50% fat, but you are burning more calories overall. This zone is for endurance training. Your respiratory system, heart and blood vessels, grow stronger.
Zone #4: Anaerobic Zone (80-90% of HRmax) This high intensity zone burns more carbohydrates and less fat, but overall calories burned is higher than the previous three zones. Benefits of anaerobic training include improved oxygen consumption and higher lactic acid tolerance for enhanced endurance.
Zone #5: Red Line Zone (90-100% of HRmax) Only the most physically fit exercisers should spend any time in this zone. Can be used as part of an interval training regimen.
excerpts from, "Own the Zone", ACE Certified News, Chris Freytag, April/May 2007