one thing that only occurred to me really recently for some reason is you know how people who start lifting heavy and building muscle will talk about ‘having more energy’ at baseline as one of the benefits? if i’m not misunderstanding the biology here that’s not just down to some kind of Healthiness Aura healing your weary soul or whatever, it’s that the more skeletal muscle you have the more actual physical space you have for glycogen storage. you feel more energetic bc you literally have more available energy
@closedcaptioning yeah they do! from the wikipedia article on glycogen:
the 400 grams thing is an estimate, my point is that number can be directly increased by adding muscle mass. iirc i’ve heard the glycogen storage capacity of a relatively well trained average sized athlete estimated at closer to 700g. there’s definitely other factors at play here like neurological muscle recruitment and improved efficiency but that’s still an additional 300 or so grams of short term energy just ready to go
i'm pretty sure you're right that more glycogen can be stored with more muscle mass, though apparently it can't be moved from muscle to muscle
for full context / it's a nice explanation / thank you for getting me to read this section, the paragraphs in Marathon Excellence talking about it
When glucose is used for energy in a muscle fiber, a phosphate ion is tacked onto the glucose molecule to convert it into G6P. Glycolysis quickly splits G6P into pyruvate which is then converted to lactate, shuttled into the mitochondria, metabolized to acetyl-CoA, and oxidized for energy to produce ATP. Glycogen is a very large molecule that functions as a warehouse for glucose. A typical glycogen molecule might contain tens of thousands of glucose molecules fused together. Glycogen stored in the liver can be broken down into glucose, which is then shuttled back to the muscles via the bloodstream. However, muscles also store copious amounts of glycogen, and this intramuscular glycogen is responsible for the majority of the carbohydrates you burn during running. In both the liver and the muscles, glycogen's large, sprawling molecular structure means it binds to a large number of water molecules, which get stored alongside the glycogen molecules. Three to four grams of water are stored per gram of glycogen, and this water acts as a "free" source of additional hydration. [...] Intramuscular glycogen is oxidized almost exactly the same way as glucose. There's one relevant difference, though, and it has to do with how individual glucose molecules are removed from the giant chains of glycogen. When a glucose molecule is leaved off from glycogen, it doesn't actually come off as glucose -- it comes off as G6P. In the liver, this is no problem: an enzyme rapidly converts G6P back to glucose and it's sent away in the blood. Muscles, though, lack the enzyme to convert G6P to glucose. As a consequence, our body cannot directly move glycogen from one muscle to another. For example, if our quadriceps are running low on glycogen, there's no way to transport any glycogen from other muscles to help out -- that muscle is stuck with only its locally available intramuscular glycogen.
so for short, that i guess that means that if someone only does upper/push/pull days, they're not going to be able to walk forever.
but i'm grumpy because he usually cites a bunch of stuff and doesn't cite this because i guess it's just common knowledge for the sports science people grumble grumble
oh yeah, when i try to search for stuff about muscle glycogen content, there's a bunch of papers ... from the 90s and earlier. so i guess it's fairly settled.
this meta-analysis from 2018, Skeletal Muscle Glycogen Content at Rest and During Endurance Exercise in Humans: A Meta-Analysis, supposedly talks about trained subjects storing about 30% more than untrained subjects.
and i got the paper, so here we go:
nb this is in mmol/kg, not g/person. not sure how many g of glycogen are in a mole of glycogen.
70 vo2max is pretty trained, yeah
