Unfortunately, unless you do a test to measure your max HR, the zones etc can be off - basically meaning that the level at which you think you're training, is in fact not having the effect it's supposed to.
I've heard of people saying "I went above my MAX Heart Rate in my race at the weekend!!!" - Which of course is impossible... they're simply saying they achieved a higher Heart Rate than the 220-age (or other) formula predicted as their MAX HR.
To truely find your Max HR you really do need to put your heart and soul into the test, it bloody hurts! But unless you do, then you won't find out what your Max is! If you want to follow training by your Heart Rate, then yes it's very effective, but you have to do it properly... otherwise you'd do just as well to follow a normal training schedule and use your natural 'perceived exertion monitor'
