Hello Ardent Cyclist , welcome to TE

There has been a LOT of talk about shifting, including quite recently. A quick search with the keyword "shift" or "gear" should help. The following thread will help, too.

http://forums.teamestrogen.com/showt...highlight=gear

As for the lactate threshold (LT), if I remember correctly, it's the point (heart rate) at which your body starts having trouble managing oxygen because the demand is too high, and produces lactate like crazy. That's bad. You can't work for a very long time at that rate. It also basically corresponds to the stage at which you go anaerobic.

According to my coach, no more than 10% of our training should be above LT. It's important to go there once in a while, so your body adapts. If you train correctly, you can get your LT to go higher and higher, so you can work for longer times, doing a harder effort. But if you spend all of your time there, you're not doing much good to yourself (and not riding for long either!).