Given that dieting is somewhat important to cycling and racing, Smartt/RST's comments got me started doing a little 'research':
According to the Power-FAQ
(1) work reported from powermeters will have to be adjusted for thermodynanic efficiency(
TE) to get the total metabolic work (
MW): that work your body has performed to produce the net effect that the powermeter accurately reported.
The Power-FAQ states that TE can be expected to lie between 20% to 25%, from individual to individual.
(2) and
(3) verifies this to some extend, and also adds evidence that TE varies with
intensity and
pedal rate. Based on TE, a reported energy expenditure from a powermeter might very well add up to quite a different total energy.
Example:
Based on one of my own rides: 2 hours total, mostly endurance with 4 muscletension workouts (5 minutes each) thrown in.
SRM-data:
Work: 1503 KJ (yes...I know I'm a slacker
)
Duration: 126 minutes
With TE =
25%:
MW = 6037 KJ (11,45 KJ/min)
With TE =
20%:
MW = 7546 KJ (14,31 KJ/min)
This is quite a span. Given that my TE hasn't been lab testet, there is pratically no way to know for sure what my MW was.
Turning to the other option under discussion: Polars
OwnCal method. Evidence is available to suggest that this method has some validity
(4). Some of the research shows quite respectable accuracy: "
the error of estimate (mean+SD) for OwnCalS was -0.7+1.3 and -0.3+0.8 kcal/min for men and women respectively". Still quite a span though, and MW might vary accordingly.
What to do?
Well for any of the approaches to work you need to narrow the factors that influence the predictions...obviously
The powermeter method would seem to only need you to determine TE and you be flying. Given the evidence in
(3), a more sofisticated algorithm taking intensity and pedal rate into consideration might produce quite valid results.
Polars OwnCal relies (as far as I can tell) on weight, max-HR, VO2-max (or Polar ownindex), and your own interpretation of atlethic ability. The Polar S-series has protocols for estimating these values.
My
personal protocol is currently based on the Polar, and is very simpel: Based on the HR-monitors estimated MW I consistently go with a daily 2000 KJ dificiency. If I continue to drop weight at around 0,5 KG pr. week the protocol is working
. I update weight frequently, VO2-max every 4-6 weeks and max-HR every 6 months. So far(2 years and running) quite stable and results are as predicted.
The same protocol could be used with a powermeter, perhaps using, different TE's in base, build and transition-phases. Going with a TE of 25% might get you a long way though!
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To anyone gotten this far, I apologize for the lenghty post, and I hope I got most of it right
References:
(1)
http://web.archive.org/web/20040201233725/http://www.midweekclub.com/powerFAQ.htm#Q23
(2)
http://jap.physiology.org/cgi/content/abstract/38/6/1132
(3)
http://jap.physiology.org/cgi/content/full/93/3/823
(4)
http://support.polar.fi/PKBSupport.nsf/ALLDOCS/42256C2B001E0F6A422569BA0037881B?OpenDocument