Maximum HR isn't a terribly important number. It varies from person to person and has little or nothing to do with how fit you are. In my own case, I'm 59 and still see numbers in the low 180s when trying to keep up with the kids on the hills.
A more useful number for training purposes is your LTHR (lactate threshold heart rate) which is, broadly speaking, the highest level of effort you can sustain. Above it you start to redline quite quickly and have to back off. You can test for it by warming up, then going as hard as you can maintain for 30 minutes and take your average HR for the last 20 minutes of that half-hour. That will be a reasonable approximation of your threshold.
Then set your training zones on that basis. Z1 65% - 80% LTHR. Z2 81% - 88%. Z3 89% - 93%. Z4 94% - 99%. Z5 >100%.
Use Z1 for recovery rides. Most of your training should be in Z2, especially when building a base. The top of Z2, shading into Z3, probably gives you the biggest bang for your buck in terms of building aerobic capacity. Inserting some lengthy intervals in Z4 will tend to push your threshold up, and if you want to get adventurous try some "over/under" intervals - 2minutes in Z4 followed immediately by 2 minutes in Z5, repeated three times for a twelve minute interval session. Warm up first and warm down afterwards, and don't do this every day.
Retest for LTHR every month or so. You'll find it creeps up over time, so you need to recalculate your zones.
FWIW, my LTHR is currently 162. And when I was still racing, last year, my average HR in most races was around that figure, usually peaking in the high 170s and dropping into the 150s between surges. Which is exactly what one would expect.
Last edited by chasm54; 07-31-14 at 08:49 AM.