Originally Posted by
mr_pedro
I have been researching and experimenting lately with fueling during work out. Regarding your calculations on how much glycogen you have stored and how much you are burning, the glycogen supply in our body does not work like a fuel tank in a car where you can go at full speed until it is empty. Rather as your storage gets depleted, it will start to limit you max output a long time before it runs out.
So if you intend to go at low Z2 intensities, it is possible to just rely on stored glycogen for an hour or two, but to go at close to your maximum for longer than an hour you need to start fueling.
Then there is another aspect where fueling helps even for 1 hour rides of intensity sweet spot and above (>90% FTP), it brings the RPE way down. I can perfectly do a hard Sweet Spot ride for one hour without eating, but it is hard. When I started doing these efforts with carbs on the bike it just felt amazingly easy.
For intense workouts of Sweet Spot and above I go for about 90g per hour of sugar in water, with a pinch of salt and some citric acid for taste. And I start drinking from the start.
I was doing a long series of Z2 rides, riding every day for 1-2 hours. I noticed that I kept losing weight, but at a greater rate than could be explained by fat burning. Sure enough, I got weak and had to take it easy for a few days. Glycogen depletion, just like you're saying. No bonk but weak. After that, I started looking at my kj for similar rides I'd done. I took half of that number, subtracted the calories I thought I might take in during the ride, and then prepared a carb/protein bottle for the frig with that many carb calories in it. Boom, strong every day, no more weird weight loss. That's a rough approximation of course, but it works and it looks like I could vary the calories by small amounts to change weight over time, 1 or 2 tenths of a lb./day.
For long SS rides, 60g/hour is the usual "during" dose and then make up the rest by looking at kj after. That's a lot to digest during though, have to see what you can get by with. Many riders can get by with just taking a swallow of liquid carbs from time to time for quite a while. Fools your body.