HEART RATE ZONES
Athletes have been using heart rate as a measure of intensity for a number of years now. According to Wikipedia, the first wireless heart rate monitor was invented in 1977 and retail sales started in 1983. Your heart rate zones can be calculated as a percentage of maximum heart rate or as a percentage of threshold heart rate. Some of the methods that use maximum heart rate to calculate zones include: Age-Adjusted Method Karvonen Formula Leger Formula Some of the methods that use threshold heart rate to calculate zones include: Andy Coggan Method CTS Method Joe Freil Method I recommend using threshold to calculate your zones. Maximum heart rate is much harder to test and is generally more variable on a day to day basis.