RockyMtnMerlin

Here are some thoughts from Joe Friel, author of "Cycling Past 50."

"But bear in mind that determining heart rate training zones is best done by using lactate threshold heart rate rather than max heart rate. Treat max heart rate as merely an "interesting number."

I use that book a lot. Even if you are not into racing it has great tips for training for longer rides and touring. It has his method for determining lactate threshold heart rate (LTHR or sometimes just LT). It is also interesting to note that (unlike Max HR) this number is variable with fitness level, sleep habits etc and should be tested periodically. Having said all that 128 sounds kind of low. I assume that you did check with a physician before you started your program.

I googled around and couldn't find a concise description of his method to cut and paste here, so best to try to find the book (or another source with a do-it-yourself LTHR test). It is easiest to do this with your bike on a trainer and with a friend to write down your numbers for you. But you could do it yourself.