Setting your power zones is important if you want to analyse your training. By analysing your results you can identify different levels of peformance effort within certain power zones. Working out your power zones is easier on an indoor trainer with a power meter as wind does not play a factor and sudden elevation changes are omitted.
Power zones are defined as a percentage of your FTP (Functional Threshold Power), which is the highest power output you can achieve in one hour. To work out your power zones, you need to establish your FTP, which is measured in watts. The easiest way to do this is to do a CP20 test, which is basically a 20 minute Time Trial, though Joe Friel suggests a 30 minute test at 0% gradient:
The Power Zone (CP20) Test
Set up your personal power training zones using the following guide (from Allen and Coggan, Training and Racing With a Power Meter):
The more times you do this test the more accurate the results will become since there is a learning curve associated with such an effort. This is best done early in the Base period and then every 4 to 6 weeks thereafter. Click here to download some Conconi TTS files.