Author Topic: GOVSS -- Underestimating Power?? (Read 7614 times)

ethanoconnor · « **on:** October 02, 2006, 10:20:15 PM »

Hi there,

I'm really excited about the GOVSS feature -- it seems like a great tool for tracking total training intensity over time and it fits with what I feel is the way I want to evaluate my runs.

I do have a question about the power estimates being given, however. Here's an example from a run I just finished:

Distance: 2.49mi
Time: 21:21.0
My Height: 1.76m
My Weight: 70kg

Average Power: 265.82W
KCal Expended: 85.16

Which is waaay below the traditional rule of thumb of 100KCal per mile. My initial thought was that the calorie calculation was off, but it is at least roughly consistent with the average power:

265.8W * 21:21.0 = 81kcal

So, I guess there are two questions:

Is a 155 pound man running at an 8:30 pace really only burning 250 calories an hour? The figure from the method of McArdle et al (from _Exercise Phsiology 3rd Ed._, Lea and Febiger eds., 1991) would be about 286 calories and 805 calories per hour (http://www.sdtc.com/cal.html)

And, less critically, why the discrepancy between the power*time (81kcal) and the calories expended reported by TopoFusion (85kcal)?

Thanks for any insight!!! TopoFusion rocks

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ethanoconnor · « **Reply #1 on:** October 02, 2006, 11:16:31 PM »

Ah -- I had a thought while in the shower after the run analyzed above. I didn't have 1-per-second logging turned on. Could that fact interact with your implementation in such a way to cause this sort of problem? If so, maybe a check for the trackpoint interval and a warning in the run dialog would prevent some confusion. If not, never mind

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Krein · « **Reply #2 on:** October 03, 2006, 07:16:49 AM »

Oops! The explanation that Dr. Skiba sent me on the GOVSS dialog got chopped off at the bottom. It was supposed to have the following paragraph at the end:

Kcal: This is not how many calories the workout burned. This is the actual external work you have generated. Depending on your own personal variables you probably burned at least 2x as many calories.

I've asked Dr. Skiba to check out the forum and help answer this and any other questions.

ethanoconnor · « **Reply #3 on:** October 03, 2006, 07:47:19 AM »

Interesting -- so this is a calculation of some sort of "net power" excluding base metabolism and inefficiencies in converting metabolic power to locomotive power...

This makes the numbers make quite a bit of sense, since typical running efficiencies are around 35-40%, and my base metabolism over 21.3 minutes should be around 30 calories, so:

(85 / .35) + 30 = 272 calories, which is right in line with traditional calculations for that effort.

Cool! I guess then my only remaining question is again on the mismatch between AveragePower * Time and the calorie calculation. It's a small mismatch but I think Average Power would have to mean something other than I expect for that mismatch to occur. Just trying to get my head around all of this since I think I'm going to take the plunge and base my training on it for the next 6 months as an experiment.