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  • Each day I ride, I'll post my power file here. I use an iAero III and iBike software for Mac (files from 5/09 and earlier were from a PowerTap and Saris' PowerAgent software). The file will give you all the same information I have. If you have any questions, leave them in the comments and I'll answer them there.

    I am a 170lb Cat 3 road racer.

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« Power File 3.1.10: Mormon Hill Repeats | Main | Power File 3.10.10: 10s and :30s »

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Comments

Cliff Dog

Getting an Intensity Factor of .92 to happen in 51 minutes is awesome.
wham, bam.

Mike May

Yeah, for an outdoor workout it really surprised me. I'm in the 90s in IF all the time on the trainer. Do you know how NP is calculated? There's got to be some intensity multiplier in there, right? Most of the ride was below 200 watts, but there were about 10 minutes around 400 watts, and that brought the NP up to 276, even though the Avg Power was 100 watts lower.

Joey Numbas

I'm a little late to the table on this one but since you asked for it, Da Numbas will respond.

They may have changed the NP calculation since I last knew it but here was what Andy and Hunter (at least I think it was them) originally came up with: Normalized Power is calculated by breaking down the time sample in question into much smaller chunks (again, the original formula calls for 30-second chunks but that may have since changed). You take the average power for the 30-second window and raise it to the 4th power. Do that for all 30-second chunks in the total time sample and take the average of those numbers. Take the fourth root of that average and you have NP.

As you can guess, the forth power concept puts a premium on the higher wattages (i.e. the "intensity multiplier" you refer to above). To prove it to yourself, you can take an easy example (e.g. a 20-minute block and assign 10-minutes of it @ 100W and 10 minutes @ 300W; you know average will = 200W but you'll find that NP = ~253W.)

Mike May

I like your explanation. It makes me feel like I'm 4x as fast as I really am. Or even Fast to the 4th, which I think is even more.

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