Just note that the numbers for max HR are estimates based on measuring lots of people and trying to find a rule that fits them all.
It not right for everybody. Your max HR is whatever you measure it to me. You can either have it correctly measured at a fitness centre where they will get you to execrise under controlled conditions, or you can measure it yourself if you think can you are fit enough, BUT ONLY IF YOU ARE FIT ENOUGH. If you have any doubt, don't do it.
Warm up throughly, and go to a base of a long hill (you are stuffed if you live in the Fens). Run up the hill hard for 20 seconds, stop and jog back to the bottom. Note your max HR during the run. Repeat 3 or 4 times. As you become tired your max on the runs will start to become less and the previous run will have acheived your max.
That's your true figure. The book mentionn by DBD is very useful.
I became a HRM bore, then realised that having a machine telling me what to do was spoiling my enjoyment of just being out there running. So mines gathering dust. Anyone out there want a free HRM and book?