Avg power higher than normalized power?
I did a new bike test this morning and something strange happened. On both my 5' and 20' tests, my NP was slightly lower than my avg power (2 watts for each test). The other intervals this morning, which were basically wu's and a cd, np was higher than avg power. I'm not sure why this happened and the only major difference is that I starting using a quarq this week as opposed to a powertap. Quarq seems to be working fine, calibrated, etc. Anyone have an idea as to why results would come out this way?
0
Comments
Common explanation for this has to do with the way the #s are calculated.
AP is calculated on a second-by-second basis (possibly with a 3 second lag if you have "3 sec power" option). NP is calculated with a 30 second lag. Meaning it uses the previous 30 seconds measurements on a rolling basis to give the current/total NP. Some algorithms deal with this by not showing the NP for the first 30 seconds, others simply include the 30 seconds prior to the interval start as part of that intervals NP. So if you were going easier just before the 5 and 20 minute tests (duh!), your' NP will be lower than the AP for that interval.
So for shorter intervals, especially on a trainer where you are presumably riding very steady with no curves, slowdowns for traffic, hills, etc, it is possible to have an AP higher than NP.
AP is the true average power over the interval time
NP is how it felt to you if there was a lot of coasting or spiking, or the true cost to your body... they should be the same if steady but this is less likely the longer you go
AP is what moves you down the road...
In this case use the AP the higher number! :-)
Having NP be lower than AP is pretty uncommon, and Al and Tim described it's really a technicality of the way the NP algorithm works rather than an indication of any physiological phenomenon except for one, it requires that your NP and AP be extremely close to begin with.
So really this is just a sign that you are riding extremely steady to begin with, a feat that is certainly more difficult for longer intervals and quite impressive if you are spot on your target power for a full 20' set.
Seeing NP < AP on the road is a different story due to road undulation and other environmental factors, it should be more difficult to replicate on the road. If you have a long variable ride that results in a NP being lower than AP, the cause is almost always that your computer is set to drop 0's from the AP calculation.
When doing my 5 X 1'(1') intervals at Z4, I should record my AP (which is higher) and not my NP (which is lower). This is because as Al Truscott stated: "AP is calculated on a second-by-second basis (possibly with a 3 second lag if you have "3 sec power" option). NP is calculated with a 30 second lag". Therefore, my AP is the true measure of my interval.
Since we didn't do any of these in the OS, I forgot and just want to make sure I'm consistent with the way we in EN do this. It's been so long since I've done these!
Thanks,
Joe
Because of these artifacts of the calculation that Al is talking about, you sometimes see other strangeness, such as a VI that is less than 1 for intervals while riding on a trainer or on a long flat section of road.
A lot of times, leading into an outside test, I will be coasting (zero power) leading up to the test, and only hit the lap button to start the test after pedaling for a couple seconds. this has the potential of adding nearly 30 seconds of 0w into the NP calculation for the interval.