This is what I have gotten from the cycling books that I have read. A lot of the training percents they give now are actually based on your Lactate Threshold (LT)and not Max heart rate. Just in case LT is considerd the highest heart rate you can maintain for 30 min to and hour with out fatigue.

It more specifically means the heart rate you can maintain without producing more lactate then your body can buffer in this time period. Then they set up the training zones based on that. I go buy anything under about 96% of LT is either recovery or endurance.

96% to 105% is the training zone where you usually time trial at while racing. This zone will help you gain the endurace to time trail and hold a pace at or slightly above LT. These can actually be used to help raise your LT. The last training zone is known as true zone 5, red line, I can't hold it long, it is more then 105% of your LT.

In my personal case this zone is anything above 200bpm or roughly 93% of mhr. And for everyone the actual heart rate numbers will be different but not the percentages of LT.

To race you will have to be able to spend time in the upper two zones. In fact you should train here twice a week or so after you put in your base endurance miles. Note in zone 5 six minuets seems to be considered a long interval, and if you are in the rate range it should be near impossible to do more then one or two at your riding level. These are very hard and painful as the ride goes on. Feel free to puke when riding here.