As you gain fitness, you'll begin to find your target ranges consistently too easy and will therefore need to adjust them upward. You can make this adjustment in one of two ways: by informally tweaking the numbers at each intensity level to fit the "feel" of that intensity, or by repeating the 20-minute max test and recalculating the power zones based on the new result.
Crunching the Numbers
You can also use power data from recent training to guide your future training. This requires that you download data from each workout onto your computer and study it for patterns and trends. Most power meters are sold with basic software that you can use to log workouts and perform simple data analysis. The most basic thing to look for is a trend toward increasing power performance in similar workouts as your training progresses. If you see this trend, your training is on target. If not, your training needs to be adjusted.
"Until we had good software that allowed us to track changes over time, the power meter was really just a toy," says Hunter Allen. "Now we can answer the question, 'Is the training that I'm doing really working?' If it's not, I can make changes quickly."
Allen's Cycling Peaks software is a deluxe aftermarket program that allows you to take the analysis to another level. With it you can track your power-to-weight ratio, monitor how much time you're spending in each intensity zone, "normalize" your rides to eliminate the sections where you aren't pedaling (i.e. descents) and much more. You can download Cycling Peaks software for $75 from www.cyclingpeakssoftware.com.
A Question of Cadence
Another use for power data analysis is finding your most efficient pedaling cadence and gear selection for various riding circumstances. Joe Friel does this with his athletes using a frequently repeated 30-minute time trial workout.
"The first time I have the athlete do it at their natural cadence, whatever that may be," he explains. "Then I'll have them do it again three weeks later at a cadence 10 RPM below what they did the previous one at. And then three weeks later do one at 10 RPM above the original cadence, and then we come back and do it at what they feel like again. The data we gather -- average speed versus power, heart rate versus power -- begins to tell me a little more about the athlete in terms of cadence. And sometimes you need to make changes in cadence."