Confused about setting Threshold Power

TMD

I've recently purchased a Powertap SL. I've been riding with it for almost 3 weeks. My plan for the 1st month of use is to "ride and record" - i.e. just do my normal riding and download the data to CyclingPeaks before I undertake any of the more structured test outlined by J. Friel, A. Coggan, etc.

The one thing that I am confused about, however, is based on the the rides I have done to date, what value I should use for setting my initial Threshold Power. Within the CyclingPeaks program I've observed three different values for power depending on whether I look at: Average Power (my Powertap is set to include zeros), Normalized Power from the ride summary data, or Mean Maximal Normalized Power. Below are the values I've observed for each (based on about 6 rides):

Avg Power: 30min = 235, 60min = 220
Normalized Power from Ride Summary: 30min = 275, 60min = 271
Mean Maximal Norm. Power: 30min = 289, 60min = 274

I primarily ride on rolling terrain and, as mentioned, have the Powertap set to include zeroes so I understand why Avg Power is lower, but I'd love to get some feedback as to what others would recommend I use to set my initial Threshold Power level?

More background: I'm a 34 yr old, relatively new racer (2nd yr), and occasional triathlete. Height 5"11', Weight 160lbs. I have two small children at home so I don't get to train as frequently as most of my teammates - so my intent with purchasing a Powertap is add more focus to my training, allowing my to train more efficiently and effectively in the time I do have.

Woofer

How about this - for a one hour ride, go as hard as you can for that hour. Use the average power for your threshold power. How are you defining threshold power? I am almost quoting the Coggan article on functional threshold power. You are asking for something that almost requires a structured test so you can't have it both ways. The other way Coggan recommends is the 2x20, with caveats. You need to read Coggan on "training and racing with a powermeter: an introduction", and if you've already read it, read it again.

RapDaddyo

There are two separate and completely independent issues as to the question of what your threshold power is. The question you seem to be asking is what setting you should use for threshold power in CP. Whatever you put in for threshold power has only one consequence in CP, the bucketed time by training zones (interestingly, CP calls them zones and AC calls them levels). It doesn't affect NP, AP or any of the power computations. It only affects the bucketing cut points for graphs when you select bucketing by training zones. The other, more important question is what power you use to define your training levels. This number is important because it determines your training targets for all levels. The gold standard for this number is your 1 hr maximum sustainable constant power. But, an equally valid basis for this number is to ride for an hour at your maximum (relatively) constant power and use the computed NP. Another basis for this number is the power at which you regularly do L4 interval repeats (e.g., 2x20s). It looks to me as though your threshold power is in the vicinity of 275w.

biker-linz

I'm not sure I'm with you here RD; are there two places where threshold is entered on CP? Otherewise threshold surely does have an influnce on the program's calculations of NP, TSS and IF.
FWIW there's another 'quick n' dirty' technique which can sometimes be used to estimate threshold. If you pull up a histogram of power for the last 28d and reduce the bucket size to 5W you will typically see two 'shoulders'. The bar just before the large drop-off in power after the second shoulder is often a pretty good estimate of threshold power.

L.

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TMD

I do agree with you that I'm trying to do an initial gage of my threshold power for two primary reasons: 1) It will help me identify my training zones/levels when I begin my more formal offseason workouts 2) It will make the IF and TSS scores more meningful and hopefully valid.

My followup question, though is that if I do bucket the last 28 days: would you recommend using avg power or normalized power?

TMD

I have read the piece - more than once. My post indicated that for the 1st month or so, I'd like to just conduct my normal rides and routes and observe what the data that is produced. I plan on doing more formal testing after that point. My questions were about estimating Threshold Power without formal testing - which is also discussed as a valid alternative on the CyclingPeaks site. I realize that after formal testing the value may change, but I'd like to use an initial estimate during this period that is more than "just a shot in the dark."

RapDaddyo

Threshold power is used to calculate TSS and IF, but not NP. NP is calculated with the following algorithm:

• Starting at 30 s, calculate a 30 second rolling average for power
• Raise the values obtained in step 1 to the 4th power
• Take the average of all the values obtained in step 2
• Take the 4th root of the number obtained in step 3 [normalized power]

I have replicated this algorithm in a pacing strategy optimization spreadsheet and tested it against actual workout files. It is the algorithm embedded in CP.

RapDaddyo

Based on your rides to date, it appears to me that your FT is at least 274w. The issue is, what was your intensity of effort in the 60min segment of that ride? One way to gauge that is to look at the metrics of that 60min effort. Unfortunately, it takes a few steps to find this specific range (unless there's a trick I don't know about). The chart on the Athlete's Home Page will identify the date of the workout of your peak 60-min NP. When you go to that workout file graph, the max 60min number is AP, not NP. But, if you click the box to the far left of that row it will highlight (in black) the workout file range for that row. Then, if you use your cursor to select that range (dark blue), you will get all the metrics for the range, including NP. It may be off a bit because highest AP and highest NP are often not exactly the same range in a ride. [Of course, you could also export the workout file as a CSV file, import it into an Excel spreadsheet, compute NP for every 60min segment and find the largest NP; it's really not that hard. Maybe the CP boys will make it easier in the future to find such ride segments.] Once you find the range, look at your avg HR during the effort and compute the percentage of MHR. If you have an idea of what your HR/MHR ratio is at your max sustainable effort, you might be able to guesstimate how close to max effort you were during that ride segment. Or, if it was only a few days ago, you might recall what your RPE was.

TMD

Thanks for your thoughts, this forum has been quite helpful for this power newbie. I think I understand what you are saying above, so just to clarify - the second line of power data that I posted in my original post was Normalized Power that I observed by going ride-by-ride through my Athlete Calendar and looking at the summary data for each time interval. I think that is similar to what you are suggesting (CP is on my home computer so I can't verify until later today)? If that is the case, then if I understand correctly you would advocate using 60min NP observed during a ride as the value to use for my initial Threshold Power? Using the data above it would be 271.

RapDaddyo

Lindsay, my main purpose in pointing out to the OP that FT is not part of the NP calculation is that NP can indeed be used for his stated purpose. If FT were part of the calculation of NP, it would be Catch-22: "NP will help you estimate your FT, but only if you know your FT." Most of our rides are variable power rides and AP would understate max sustainable CP power. But, NP brilliantly solves that problem and converts a VP effort to a CP equivalent. NP is so cool!

RapDaddyo

Actually, I'm referring to the third line in your OP, where your Mean Maximum NP was 274w. That number comes from a 60min segment of a ride. The chart will give you the date. Then, there is a little effort involved to find that specific 60min segment of the ride. It would be nice if one could double click on the Mean Maximal NP chart and it would take you to that 60min segment, but it doesn't work that way. You have to go the ride graph and find it. Or, as I said, export the data to an Excel spreadsheet and run an algorithm to find it -- basically, a rolling 60min NP computation.

RapDaddyo

And a CP newbie. CP has a wealth of features, all the handiwork of Andy Coggan. Check out NP, TSS and IF. And, there will be more features in the next version of CP. But, these three statistics alone are huge. It is worth spending some time really understanding the underlying computations. I can't figure out which I like better -- my PT SL or CP.

acoggan

Part of the design philosophy for CyclingPeaks has been to offer people all the functionality found in other programs, plus "extras" such as normalized power. Thus, the ability to call up a file as you describe should be in there, because it is in the SRM software. Unfortunately, developing a program from scratch on basically a shoestring budget is huge undertaking, and not everything, including this feature, made it into version 1.1. Hopefully this will be rectified in a future release.

RapDaddyo

First, I'm not complaining about CP. I love it. Second, for me personally it's no problem. I just export the raw data into an Excel spreadsheet and do whatever I want with it. If I can't do what I want with Excel, I just go to SPSS. And, I know all about developing programs (and companies) on a shoestring budget because I've done it a couple of times and am doing it right now. My comment is more like a line item on my Christmas wish list. The contributions that you and CP have made to cycling with power are huge and I doubt that more than a small fraction of the cycling population (even those with PMs) fully appreciate NP, IF and TSS. I do.