The basic formula for guessing your max heart rate or MHR is the 220 - age. From personal experience I can vouch that this is normally wrong. My absolute max has been, since I started measuring it, around 163. This will make me 56 according to the "formula" and I was 46 when I first measured. My friend and Epic partner Kevin can reach around 180. He is a year older than me.
The best is (maybe not the most scientific) to test your max by finding a nice uphill and after warming up just open the taps and get someone to chase you. When your lungs explode and your legs fall off and you push just a little harder still, you have maybe reached your max.
Now determine your resting Heart rate or RHR. This can vary with fitness level. Mine is currently 48 but has been as low as 38.
A nice formula to calculate training zones is then (MHR - RHR) x % + RHR. Replace the % sign with 50, 60, 70, 80, 90.
My zones then is
1 = 50-60% 106-117
2 = 60-70% 117-129
3 = 70-80% 129-140
4 = 80-90% 140-152
5 = 90-100% 152-163
Now this can become very complicated if you want to start adding names to each zone and times per week training in each zone, and for that POLAR has done some work in developing a spreadsheet that one can use to plan your weeks. It used to be on their website, but has since been replaced by sophisticated (read expensive) software. I like to use it purely as a guide and to force some discipline into my training. I am sure there are better programs, but they come at a price.
The bulk of your training should be Base and that is riding in zone 1 and 2. Zone 5 is to difficult for me to train in, so I normally don't...
So maybe now it will make a bit of sense if I report my weekly progress through my getting fit again campain (pun intended). Feel free to add your comments, that way I can learn more and train better, get fitter quicker and ride faster...