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Pacing and Nutrition

I never cease to be amazed at how really simple questions can become almost impossible to answer when it comes to exercise physiology.

I'm just an IT spod who has a passion for training and riding my bike. But, having bonked really badly on Etape 07 (or possibly underestimated the effect of altitude) I am determined to get it right for La Marmotte this year.

The chart above is intended to show the percentage of fuel that is derived from muscle glycogen versus fatty acids (etc) at differing exercise intensities. Basically, at higher intensities the energy derived from glycogen becomes greater and will need to be replaced on the go. By contrast, the energy derived from fatty acids will not.

Tipping Points and Sailing Close to the wind

Based upon the assumption that (a) I will carbo load before La Marmotte and will have approximately 1000 cals worth of glycogen sitting in my legs and (b) I will take on 400cals of glycogen per hour then the following table tells me how many hours I can go for at each intensity before I run out of glycogen
  • IF < .80 - glycogen levels will rise over the ride at this intensity
  • IF .85 - glycogen levels will just be maintained at this intensity
  • IF 0.93 - glycogen levels will be depleted after 3 hrs at this intensity
  • IF 1.00 - glyogen levels will be depleted after 1.5 hrs
However, the ride is comprised of, effectively, 3 ascents and 2 descents, roughly;
  • 0.5 hrs Roll from Start to Glandon
  • 1.5 hrs Glandon Ascent
  • 1.0 hrs Glandon Descent and Roll to Telegraph
  • 2.5 hrs Telegraph and Galibier Ascent
  • 1.0 hrs Galibier descent and roll to Alpe D'Huez
  • 1.5 hrs Alpe D'Huez Ascent
Which means that there is ample time between each ascent to take on fuel whilst burning very little if one sits in a group (solids on descent since riding one handed and drinking on high-speed technical descents is well beyond me).

Which means in theory the above table could be used as a pacing guide for the day. It is the maximum pace I could sustain assuming I religiously take-on my 400 cals every hour. And the small matter of having the legs to sustain those intensities on the day (threshold for an hour and a half up AdH and sweetspot for 2.5 hours being impossible, of course).

Suffice to say this is an optimum, sailing close to the wind plan. I'll be looking to put the brakes on if I start to approach anywhere near these numbers especially up the Telegraph/Galibier. The numbers are about looking at nutrition more than pacing.

The truth is, I shall be looking to enjoy the day and get round in one piece, so the chances of me pushing myself that hard is debatable. But a rush of blood and the adrenalin can do very strange things ....

Data and Research sources for Table 1
I freely admit that the last 4 columns are not as robust as they could be -- they are inidicative rather than prescriptive, so here is how I formulated the table. Since intensity is generally based upon %age of vo2max in the literature I have mapped this to %age of MaxHR using Brianmac's useful web-page (because I do not measure Vo2max). For each HR I have mapped to typical NP values for my own rides with this average HR (so whilst the power column is only really useful to me with my FTP of 290 you can make your own by applying the intensity factor instead, my MAXHR is 183 btw). The percentage breakdown for glycogen etc is based upon lots of web based research and some liberties (invalid assumtions about the mix of type 1, 2a and 2b muscle fibers - aka slowtwitch and fasttwitch) but largely comes from the following (apologies for the shoddy citations):
  • Determination of the exercise intensity that elicits maximal fat oxidation. J Acton et al.
  • Effect of Exercise Intensity on Fat Utilization in Males and Females. J Kang et al.
  • Regulation of endogenous fat and carbohydrate metabolism in relation to exercise intensity and duration. Romijn et al
  • Sport Nutrition Asker E. Jeukendrupand and Michael Gleeson
  • Ex Phiz 101. Web seminar. A Coggan

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