Originally Posted by
DaveLeeNC
This is mostly curiosity, rather than something that I need for my personal cyclling.
As I understand things my body can store about 2000 calories worth of 'readily accessible' glycogen in various places.
When I ride I burn through (power meter measured) anywhere from 700 to 900 calories per hour. Since that does not include base metabolic requirements, add another 50'ish cal per hour.
My body can metabolize fat for use in turning pedals, but that is a relatively slow/inefficient process. When I am doing my 750 to 950 cal per hour cycling, roughly half of that comes from fat metabolism (I have no idea where I got that figure, but I have had it in my mind for a while).
So if I go out and ride for 5 hours at a total of 800 cal per hour, 400 cal/hour of that comes from fat. That leaves 400 cal/hour to come from my glycogen stores which by this (questionable) analysis is about 5 hours.
So I really don't need any extra nutrition for a 5 hour ride. I have never tried that, but I doubt it. So where are the errors in my analysis?
Thanks.
dave
What is your FTP? That is ~200-300w avg for 5 hours. At Z2 you might be close to 50% fat oxidation, but at close to 100% FTP(~90% V02max) you are almost 0% fat. The distribution of the ride will dictate that percentage. There are certain programs that will estimate that based on your distribution in zones assuming your fat burning capabilities are avg. As others already pointed out the number is closer to 1500g as intramuscular glycogen is not transportable like liver glycogen. You can also get some glycogen replenishment even while fasted from gluconeogenesis of glycerin freed from triglyceride(fat) oxidation. A well trained cyclist can probably do a 5 hour ride fasted, and a pro tour rider can probably do that at 2-300W, but unless your FTP is north of 300W it is unlikely you can do so at that avg power.