I’ve always wondered how to explain recs for early fueling in longer rides (>3 hrs) with general principles that rides under 1.5 hrs even if very intense can be done with onboard stores if adequately fueled beforehand. I’m curious to know if people have stronger rides fueling early in long rides even though adequately rested and fueled coming into the ride versus waiting to take in carbs closer to 1.5-2 hour mark in these long rides. Does it make a difference?
Depends on how hard the ride starts? On really intense 2 hour rides I’ve needed to eat. And eat immediately after, always.
On my long endurance rides I always eat early. I figure the risk of not eating enough by waiting for 2 hours in to start is way worse than whatever could happen by eating early.
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My bottles are filled with carb drink so I’m fueling right away. While the body stores a lot of muscle glycogen, a lot of it is in muscles that aren’t used to spin the cranks. So rather than relying on the body to shuttle glycogen from unused muscles to the legs (or however it works), I constantly fuel such that I finish the ride only partially depleted.
Makes a huge difference in how I recover and how hungry I am later in the day.
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Yes. For endurance rides where you are going hard, fuel early and often. Don’t wait for your carb stores to run out.
I’ve been attempting to figure this out on my own…coming up with very general and fuzzy ideas. Super interesting but not a lot of detailed info out there (on the free interwebs, that is).
I’ve stated on another carbs4fuel thread that if your onboard stores are at 100%, you should be able to bang out either an endurance level ride or a VO2max session. It’s the steady SS/Threshold which really gobble up the carbs so you probably need to be aware of your capabilities concerning those types of rides.
Last year I did a lot of long Z2 rides fasted and w/o fuel and w/o problems, but I was also HFLC. This year, I’m very carbcentric but still doing long fasted Z2 rides. I start gulping liquid carbs around hour 2. The physiological adaptation gains of completing the ride far outweigh any further fat adaptations which may or may not occur after that time.
I have noticed, however, that starting to fuel half way through a ride makes me a bit ravenous for more carbs during the rest of the ride. I’m not hungry or bonking or anything negative, but just think the body knows a good thing when it tastes it.
As for completely emptying your carb stores, there’s evidence that mammal physiology maintains an “emergency” baseline level of CHO…just in case. So if you’ve bonked and need to get home, find something to scare the shazam out of you and you’ll have a fine sprint to your front door. 
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On long rides I usually start sipping carbs around 90 minutes in. And then start eating solid food 3 hours in. That has always worked well for me. Everyone is unique and needs to figure out how their own body works.
glycogen does not get mobilized, e.g. it does not get transported from unused muscle to the working muscle motor unit
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How does it work, exactly?
Curious minds would like to know. 
From my kindergarten level understanding…different muscle types (e.g. fast/slow twitch) store different levels of glycogen within the larger muscle (e.g. quad). The glycogen is then depleted at different rates depending on activity. Once it’s exhausted, that’s it. The arm bone doesn’t supply the leg bone.
[edit: that being said, a lot more muscles are at work during a bike ride than just the legs…not sure you’d actually want glycogen shuttling to be a thing as it would cause a lot more problems than just heavy legs.]
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Over the past three months, I’ve been trying really hard to dial in my fuelling and I think I’m getting close.
For longer rides of 3+ hours with plenty of climbing, I ensure that I have a carb-sentric meal the evening before.
Once on the bike, I start fuelling 20 minutes into the ride. I use 80 grams off SIS Energy in both 500ml bottles and a combination of flapjack and Jelly Babies in the pockets. I continue fuelling throughout the ride every other 20 minutes. This strategy saw me finish yesterday’s ride feeling almost as strong as when I’d started.
In short, I’d say that early fuelling in a ride is a game changer for me.
The Skratch portables cookbook has alot of good info on this. They have many charts and information detailing exactly how much you can have stored, and how much fuel and hydration you need to take in based on your parameters. They also detail how a high carb (70-80%) diet results in a high glycogen tank. Off top of my head, the difference is roughly 1500cals available for a normal diet and 2600 for high carb. And another 400cal in your liver.
Although this book isn’t free. I highly recommend it.
All of your muscle glycogen storage is local. Each muscle can only use their own. This is to protect vital organs, like the brain, which utilizes around 60% of the glucose in a day for a stagnant person.
The liver operates like a global battery for the entire body and will release glucose in the bloodstream that can be used by anything.
These mechanisms protect us from ourselves. Having the ability to starve our involuntary body functions would be really bad like @Captain_Doughnutman mentioned.
Is that ‘whole body’ or ‘per muscle’? As in, how much of that 2600cal of glycogen in stored in your legs? And depending on what kind of activity you’re doing (i.e. what muscle types are being predominantly used), how much glycogen is being used and how much needs to be replaced?
Obviously in the weeds with this but interesting and perhaps even useful.
This topic was on the podcast here:
The mechanics of how your body pulls glycogen from the muscles for energy
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In that book, the numbers they reference is just lower body glycogen. So for a high carb eater the number would be around 2600. Once I get home I’ll look up the exact numbers. They also base it on other factors like body size. They also give burn rates based on things like pace, exercise duration, and the thermal efficiency (only about 20% of our calorie burn actually goes to pedals. Rest is lost through transfer of heat through sweating).
It’s about 30 pages that help you map your hydration, fueling, and electrolyte intake based on you individually and the activity you are doing. Skratch’s idea isnt to just take in the “max” 100g carbs for every activity, but to calculate and adjust your needs for each activity. The calculations you are wanting to do for say a 1hr trainer workout vs a 3hr ride is exactly what they walk you through in a detailed and scientific manner.
The “max” 100g is really only critical for 3-6hr rides. Shorter rides you will have enough stores on board, so you dont have to run the max. Longer than 6hrs and your intensity has to decrease, which means more calories come from endless fat stores. So you wouldn’t need to run 100g/hr for most 6+ hr rides either.
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Awesome! Thanks for all that. Will have to order a copy of the book.
The book is Feed Zone Portables. Yes, it’s a cookbook, but the first 50 pages go through the detail you are looking for. I’ll run through what that would look like for me.
I’m 6’3" 180lbs. 82kg. 20%bf
In the charts, for my weight and and body fat I would have 1400 glycogen calories if I were on a moderate carb diet (40-50%), or 2400 glycogen calories stored on a high carb diet (60-70%). I’ll use the high carb number for this example. And this is just lower body glycogen.
Another chart list data for performing a century. Let’s say I do a century in 4.5hrs averaging 285w. That would be around an IF of 0.75. So slightly assuming 75% of energy use is coming from carbs and 25% from fat, we can calculate the following:
Total calories needed: 5500
Calories burned from carbs: 4125
Calories burned from fats: 1375
Glycogen onboard in muscles: 2400
Glucose in liver: 400
This gives us 4125 - 2400 - 400 = 1325 additional carb calories to intake over 4.5hrs just to finish up even. That is 294 carb calories per hour. And that needs to start from the beginning of the ride.
So if you know your power and duration. And you can come up with close enough number for what percentage of burn has to be carbohydrates. You can work backwards for any ride whether it be a 4hr ride, or even 1hr trainer workouts to figure out what you need. And this is what they detail within those 50 pages. They even discus the same thing for hydration. Most of the time for activities 3-6hrs, if we replace half the calories we burn per hour, with carbs, we will come out pretty close to the calculations.
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