Originally Posted by
Drew Eckhardt
Nope.
With decent training and diet riding an endurance pace you're still getting 20-25% of your Calories from glycogen or blood glucose.
On average you have about 100g of glycogen in your liver, and 400g in your muscles although there's no way to move it between muscles or even fibers within the same muscle - what's in your type iix fibers can't be used for endurance riding.
If 1/3 of your muscle glycogen is accessible, that gives you 233g at 4kcal each totaling 932kcal.
At 20-25% glycogen, and 20-25% net metabolic efficiency that gives you a range of 3101 - 4845 kj out before needing fuel.
932 / (.2 to .25 glycogen fraction) / (1 kcal / 4.2 kj / (.2 to .25 efficiency))
One Watt = 1 joule per second; so 1W * 1 hour = 3600 joules or 3.6kj.
At 150W you output 540kj/hour and you could last 5.7 - 9.0 hours
At 200W it's 720kj/hour and you'd run out in 4.3 - 6.7 hours
150W is a 17-18 MPH average on flat ground with false flats, corners, and slowing for traffic controls; 200W 20-21.
You probably have enough reserves for at least a metric century, and maybe an imperial one.
It depends on whether it's a steady effort and training/diet.
Steady efforts are self-limiting. Some one with a 300W FTP would output 1080kj in an hour, although after that it's over. Some people get under 60% of their energy at FTP from carbs and 50% at a tempo pace and will be fine. Passing five hours your maximum pace is going to drop to your aerobic threshold which spares your carbs.
Mixing hard efforts and endurance riding for a few hours (like in a group ride with hills or where you take your turn pulling) you're going to run out without fueling.
Lol, you are certainly an interesting fellow who has it all figured out. Amazingly, you have it all figured out for every other cyclist in the world. Its incredible really. You can even predict how fast I'll go on a specific number of watts. Ok, a 20k TT that I recently rode at 190 watts. Flat course, no turns, slow course conditions that improved gradually over the duration of my race, sea level, air temp 57F. What was my speed and how many calories did I burn? (No, I was not wearing a calorimeter, in case you ask. Why? Because it was a race and I am a normal human being.) Just wondering.
What I did in my response, Drew, was give a simplified answer to a guy who wants to eliminate sugar from his diet and still ride a bike significant distances. He is not someone that has the best understanding (right now) of cycling nutrition. The message I gave him is: Ride at low intensity and you can do it for a long time without sugar- for many hours and very likely for the distance you want to ride (40-70 miles). How do I know this? I do it myself, but at higher intensity than I'm suggesting for him. Its trainable. Part two of my message: If you want to ride hard, you're going to need to take in carbs and your best source is sugar. Simple, straight forward and correct advice.
Honestly there is no need to turn every nutrition, weight loss, or training discussion into a tedious mathematical exercise in which you call other people out on trivial details while ignoring the gist of their post. You are not the last word on these topics and interacting with everyone else here on the forums as if you are just gets a little exhausting. If that's your intent, carry on, I guess. If its not, then maybe take a step back every now and then and look at the big picture of the conversation at hand. OP has gotten several pretty good answers to his question already and sometimes letting someone with a simplistic question digest the answers he's already gotten is perfectly adequate.