Normalized power question...



mattmor

New Member
Sep 19, 2003
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This may be kind of a dumb question, but I still don't quite understand normalized power. I did a ride this morning- and felt pretty good for the first time in a few weeks. I looked at the attached peak 20 min and am just trying get a better understanding of NP.

I'm guessing I also need to do an actual field test for a more accurate threshold number - I'm estimating it at 250. Based on a very old field test of 278 - figuring I lost some power since then with not actually training. I also had done a trainer field test for a friend in March - 20 min was 240 watts.

Does it seem like I'm close on my numbers here? And looking at that peak 20min - can you help me understand the NP being that high? Thanks!


Peak 20min (178 watts):
Duration: 20:00 (21:28)
Work: 213 kJ
TSS: 46.2 (intensity factor 1.177)
Norm Power: 294
VI: 1.65
Pw:HR: 18.08%
Pa:HR: 14.1%
Distance: 5.812 mi
Elevation Gain: 208 ft
Elevation Loss: 228 ft
Grade: -0.1 % (-17 ft)
Min Max Avg
Power: 0 802 178 watts
Heart Rate: 80 172 135 bpm
Cadence: 15 174 83 rpm
Speed: 3.1 33.5 17.6 mph
Pace 1:47 19:19 3:25 min/mi
Altitude: 247 337 298 ft
Crank Torque: 0 1671 188 lb-in
Temperature: 68 69.8 69.3 Fahrenheit

Entire workout (147 watts):
Duration: 1:25:28 (1:36:55)
Work: 748 kJ
TSS: 130.3 (intensity factor 0.965)
Norm Power: 241
VI: 1.64
Pw:HR: 12.04%
Pa:HR: -0.07%
Distance: 23.087 mi
Elevation Gain: 657 ft
Elevation Loss: 693 ft
Grade: -0.0 % (-34 ft)
Min Max Avg
Power: 0 1212 147 watts
Heart Rate: 80 185 130 bpm
Cadence: 7 182 80 rpm
Speed: 0 33.5 16.3 mph
Pace 1:47 0:00 3:40 min/mi
Altitude: 238 365 299 ft
Crank Torque: 0 1745 160 lb-in
Temperature: 64.4 75.2 70.8 Fahrenheit
 

RapDaddyo

Active Member
May 17, 2005
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I think the best description of NP can be found at either the TrainingPeaks website or in Training and Racing with a Power Meter (Hunter/Coggan). But, the real question is what are you going to do with your power at duration number (e.g., 20MP)? If you want it for training purposes, it doesn't matter much because it is self-correcting. Let's say that you think your 20MP is 294 based on the NP of your peak 20min segment of your ride. If that's a good estimate, then you will find it difficult but not impossible to ride your 20min efforts at 90%+ of 294 (e.g., 265+). If that's an overestimate, then you'll really struggle in the 2nd half of your 20min efforts if you can finish them at all. If it's an underestimate (unlikely), then you'll finish the efforts easily and you'll just know that it's low. If you want a really solid MP at any duration, I recommend a constant power ride to exhaustion. Just pick a duration and estimate what you think your MP is (e.g., 294 for your 20MP). Find a place where you can hold a constant power for at least 25 mins (I prefer slight, constant upgrades into the wind). Then, you just ride your target power until you can't hold it any longer. So, it's not exhaustion in the sense that you fall off the bike. Rather, it's your maximum duration at a given power. If your estimate is in the ballpark, then your duration will be 20min plus or minus a couple of minutes. BTW, if you have not done such a ride, they aren't much fun in the last few minutes -- actually, they're brutal.
 

mattmor

New Member
Sep 19, 2003
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Thanks for the reply. I'm not making any assumptions that my threshold power is 294. I'm just trying to figure out the significance of that # in relation to avg power and possible actual threshold.

I'm sure the next step is to do a field test - to accurately have some training zones. I've just been riding around with the power meter to collect data and figure out what's what. Soon time for some threshold intervals.

Appreciate the comments.

-matt
 

RapDaddyo

Active Member
May 17, 2005
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Originally Posted by mattmor .

Thanks for the reply. I'm not making any assumptions that my threshold power is 294. I'm just trying to figure out the significance of that # in relation to avg power and possible actual threshold.

I'm sure the next step is to do a field test - to accurately have some training zones. I've just been riding around with the power meter to collect data and figure out what's what. Soon time for some threshold intervals.

Appreciate the comments.

-matt
Based on your ride file statistics, your peak 20min segment was clearly one with highly variable power output. It was either a group ride with a lot of hard pushes combined with sitting in or rolling terrain where you went hard up the frontside and then coasted on the backside or something like that. I haven't looked back at all my ride files to see what percentage had a VI of 1.65 or greater, but I think it would be a very small percentage. Normally, I would get something approaching this on a group ride with a fast group where I'm going hard on front about 25% of the time at well above my FTP and then drafting about 75% of the time at well below my FTP. The reason you can get such a disparity in NP versus AP is found in the NP formula itself. AP is a weighted average of watts weighted by duration. NP is in effect a weighted average of watts to the 4th power weighted by duration. So, any time spent above AP has a huge impact on NP.