Originally Posted by davester

How are your estimating your MHR? Reaching it quickly suggests to me that you are using the incorrect old wives' tale 220 - age method. That formula has been thoroughly debunked as irrelevant to older folks and vastly underestimates true MHR. There are a number of different methods for properly determining MHR. Probably the most common and easiest to implement reliable method is to do an on-the-bike test (with an HR monitor) where after warming up you ride up a moderate incline, progressively increasing your speed and energy output (and HR) at approximately 1 minute intervals until you become completely unable to increase further. Your highest measured HR should be at or slightly below your MHR. The problem with using the 220 - age formula and thereby underestimating MHR is that when basing your zones on that number you aren't riding hard enough and therefore won't receive the benefits of a proper training regimen.