Underfueling fatigue

I’ve been really good about fuelling for the past few months. A big dose of carbs half an hour before training, 30g simple carbs 5 mins before 80g an hour on the bike. And that’s just for the 1.5 hour tempo rides. Followed by some after training depending on feeling. On Sunday for one reason or another I skipped that, still did 80g of carbs during but missed the bigger carb pre ride. Got that hungry feeling when you start dreaming of cake 15 mins before home. Ate all the carbs basically when I got home. Was tired all day and feel pretty empty today.
Lesson learned. Fuel properly, trying to make up for not enough carbs after the ride is not the same. I’ve gone from a pretty low carb paradigm to carbs carbs and more carbs, all around training. I’m not eating tonnes of carbs the rest of the time but around training I’m eating annoying amounts of carbs and it’s working so much better for me. Better numbers and most important for me, better recovery. YMMD.



I thought the liver can store up to 400kcal of carbs. I never eat on rides <1.5h and only have fluid carbs when I go threshold and above. Pre Ride meal, yes but for such a short ride eating 80g carbs/h is a bit exzessive imho unless you’re 20 something years old and have a fast burnrate I don’t see how you’d need that amount of carbs for a short temporide.

I thought it was the other way around that the liver can only hold about 100g while the muscles can hold 400g-600g (of glycogen)

A chonk of carbs 20-30 mins before an indoor ride is risky for me if I’m riding after work and before dinner. I risk feeling tired and weak between minutes 18-28.

If I’m behind on fueling for the day/ride, then I’m almost better off going through the warmup with some sips, then start drinking the carbs after. For some reason, that transition works better and if I really did need the carbs, they catch up 20-30 mins later.

All carb-heavy meals leave me feeling achy and cranky, though. I have excellent fasted blood sugar and glucose response numbers, so who knows.

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I don’t know enough about the exact distribution but found this:

The capacity of your body to store muscle and liver glycogen, however, is limited to approximately 1,800 to 2,000 calories worth of energy, or enough fuel for 90 to 120 minutes of continuous, vigorous activity. If you’ve ever hit the wall while exercising, you know what muscle glycogen depletion feels like.

(source: The Body’s Fuel Sources – Human Kinetics)

either way, point is your body can store energy and for such a short amount of time I don’t think you need to fuel 80g of carbs per hour unless you can’t replenish the lost carbs afterwards.

If you’re used to eating or taking in carbs before a ride, your body is trained to want them. When you do not do it the body is thrown off its schedule. If you skipped them everyday for a period of time, your body would adapt.

100g of sugar is 400 kcal

You may not need to but a question could be, why wouldn’t you? I think a lot of it is all because as cyclists we all have a borderline eating disorder. Which is understandable with w/kg being so important. In an hour and a quarter tempo i get through about 1000 calories. If I rode the day before and didn’t then eat 1000 extra calories on top of basal calorie requirements then I could easily be a bit short during my ride which I assume happened. I mean, I was hungry 15 mins from home and then felt tired the rest of the day. Sounds like not enough carbs to me.

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We always hear that there are 1500-2000 cals stored in your muscles, but those calories aren’t mobile, right? I mean, when your quads start running low, your biceps don’t release their stored glycogen back into the bloodstream to be transported to your quads? So you don’t have all those calories available to your legs, though they are the biggest muscle group so they’re storing more than other muscle groups.


Agreed. Just because you can doesn’t mean you should. Once I started riding 10+hr/week regularly then that ride fueling really started to matter to me as it helped me recover for back to back days. I could probably eat back all those calories after but it just wasn’t the same. Why wouldn’t I take advantage of that time when my muscles are gulping up all the carbs that it can. Try to spare those muscles stores and give them readily available carbs. Glycogen replenishment isn’t immediate either. It can take up to 72 hours to restore muscle glycogen.

Not to mention that drinking/eating carbs during the workout can lower the RPE for the workout which helps with maintaining motivation if you can make the workouts hurt just a little less.