Why would they make such a claim? Anyone who has done keto and worked out has probably had the experience of doing quite a lot of physical activity while having had no carbohydrate intake at all for half a day before, or more.
Must see if you want to understand/practice keto right:
As far as my research into keto goes eating too much carbs kicks you out of ketosis (duh!) and eating too much protein triggers gluconeogenesis which also kicks you out of ketosis. Which is a shame because I'd be happy to eat fatty steak and fatty pork all the time!
Keto guidelines generally say 30g carbs per day and that's what I'm going to stick to (net carbs; I want to eat avocados!). So typical keto diet should work fine with what you say about carb requirement.
I don't have any particular desire to go all the way to 0 (or some really low number) and if I have some carb budget left I'm happy to get a latte. Starbucks says grande almond latte has 9g carbs (5g sugars). Perfect to tidy it up to just below 30g/day.
Since I switched to keto I have an amazing mental clarity. Literally from the moment I open my eyes in the morning I feel lucid (before I'd take me maybe 30 min and maybe a coffee to "wake up"). And I feel lucid all the way until I fall asleep (I don't get tired before falling asleep. Just go to bed, sleep). Nice and steady energy throughout the day.
Also, I feel noticeably better overall. My max strength suffered a little bit (keto can take 1-3 months to adjust) but I'm more energetic throughout the day, mind and body.
That is also my knowledge. Therefore, there seems no need for any intake of carbohydrates; So the claim about "needing carbohydrates" is not warranted (about intake, anyway)
At low circulating insulin levels, most cells in your body can efficiently metabolize fatty acids. For the minority of cells that cannot, your liver converts protein into sugar by a process known as gluconeogenesis.
It’s very possible to be a performance athlete and eat very low carb.
In a sessile starvation state glycogen stops being a meaningful energy source after 2 days, with the majority of it depleted in approximately 8-12 hrs (it's non-linear).
Depending on one's baseline physical activity and what they mean by "half a day," sure, glycogen stores can be reasonably depleted.
That said, glucogenic amino acids can replenish glucose stores, which can ultimately become glycogen. Glycogen remains low only in the context of low-carb and low-total calories, so what glycogen is replenished is soon exhausted.
It may be that you disagree, but I get the feeling that you ignored the "doing keto" part of my setup, and instead thought that the person in question was eating cake 12.5 hours before the workout. :)
The depth of color indicates how concentrated ketones are in your urine, which is impacted by (1) the amount of ketones your body is producing, and, very importantly, (2) your hydration level (i.e. how diluted your urine is).
For newbies, if the stick is pink AT ALL, congrats, you're in ketosis. Don't make the depth of color a big goal.