I wont profess to be an expert because from when I studied Phys Ed in the late 80's till now, a lot of theories and beliefs in this field has changed or turned on its head. When you only have access to a HR monitor it can serve a great purpose. It can also act as a mechanism to hold yourself back too much, and never actually push yourself to the limit (which you wont know where it is as you dont go there). Its common sense that when you get older, your max HR drops by a few beats per year. The reason why the formulas as explained in this thread dont always work,is because it doesnt take any training history into consideration. Eg. you might have been actively involved in some sort of endurance type activity or sport earlier in your life, which contributed to your heart and lungs developing etc. So naturally you might have a big and stronger heart than a fellow rider of your age. To simply use the formula you might both get to more or less the same answer, depending on yr resting HR. Now you ride together and for the same perceived effort yr HR is 120 and your partner's 130. Problem is that this number can be influenced by so many factors that it should always only be one of the measures used to ascertain your fitness level etc. These factors could include: - state of fitness - riding in a group/alone - weather - route - genes - health condition , etc, etc.... So , whilst training might not seem to be able to increase yr max HR, its true that if you are fitter than a month ago, you will be able to push yourself harder and therefore your max HR might be higher than before, but just because you have never gone there, not because the training made it higher. To use the HR as a guide to determine fitness by looking at the rate it drops after a hill climb or a session on the bike etc, is well worth the effort, but once again the factors could have an influence. Comparing that session with a similar one a month ago etc, will certainly give you some sort of indication as to whether or not you are improving or getting fitter - provided all factors are as close as possible to similar with the previous session. Best is to have your Lactate Threshold tested in a lab, that will give you the scientific answer to where the cut-off points are for the different training zones (if you use HR based training),but even those tests cant give you an absolute max HR value. What they would normally give you is the value at which your body can for a maximal effort of say 3 mins operate at before going into O2 debt (that state when you start seeing stars and holes in the ground etc..) Hope this makes some sense