In reply to Removed User:
Is it possible to determine the distance you achieved in each workout?
Assuming you were on the same route, and using the same gear, you'll have a pretty accurate correlation between power and the distance achieved in each 8-minute segment.
For my rowing and running (I don't cycle often) I find it useful to record distance, Av HR and Peak HR for every workout (plus a subjective comment on how the workout felt). I get a pretty good picture of fitness over time from this, being able to compare any given session directly with last season's results etc. Improvements can manifest either by an improvement in distance or power for the same HR, or a decrease in HR for the same power or distance. Certainly on the rower, power and distance are two sides of the same equation and are inextricably linked. For the bike there are more variables, but as Escher points out these can be reduced by using a turbo for example.
If you can broadly match last year's variables (e.g. route travelled, gear used, tyre inflation pressure, wind speed, it goes on) and quantify both sessions' absolute values (distance, height gained), you can get a fairly accurate comparison of fitness between the two. Power is only one way of interpreting the effort - distance achieved over the same course is directly correlated to power, variables notwithstanding.
Max effort testing is very reliable, but frankly you have to ensure sufficient data points if you want to be accurate. Athletes have good and bad days as you know: this can massively skew the picture if you only have limited data. IMO, trying to build up a picture of general fitness progress over a year using only two data points is (with respect) a bit daft, and potentially demoralising.
I personally don't like max effort testing, as it tends to screw me up for a few days and I've seen it adversely affect my fitness as a result, so I refer to my in-session data over time, which is a bit more gentle.
Post edited at 12:14