'07-'08 Power Profiles
The accompanying chart from WKO+ software shows the best Critical Power for every duration for the last two seasons for one of the athletes I coach. He is a 56-year-old who competes both as a road cyclist and triathlete. He is quite successful racing in both sports.
The solid yellow line is his 2007 season and the broken yellow line is the 2008 season as of last week. Across the horizontal X-axis are durations starting with 1 second on the left end and progressing beyond 4 hours, 34 minutes, 29 seconds (4:34:29) on the right end. The vertical Y-axis represents power. The low end is 0 watts and the high end is 1800 watts. (While a good rider, he's never done 1800w in his life or even close to it. Everything above about 1000w is random and incorrect data and should be ignored.)
Notice how at about 3 minutes the yellow lines separate. This tells me that as the duration of the effort gets shorter he was producing far greater power in 2007 than so far this year. I expect nearly all of the 2007 data points left of 3 minutes were produced in races. And since he hasn't raced yet this year and has been focused on base training elements (aerobic endurance, muscular endurance, force and speed skills) his upper end power has not been challenged. It's time to shift his training focus toward intervals with shorter work bouts of about 3 minutes or less done at his CP6 power (best power output for 6 minutes).
Also notice how the lines to the right of 3 minutes converge. As the duration gets longer his power output approaches that of last season. This suggests that his base aerobic endurance fitness is well developed and confirms that it's time to move on to the build period of training with a greater emphasis on anaerobic endurance.
Click the chart to expand it so you can read the comments which further describe what I see happening with his training this season.
Analysis tools such as WKO+ are changing the way I go about making decisions regarding how to train athletes. I'm a better coach and the athletes are faster because of such data.