"Ooooh, that's a really neat trick, how long does that one take to learn?"

"Usually it's only safe for jounin, who've typically been studying at least ten years, because it's chakra-intensive. However, if your chakra can't run out, then it isn't actually significantly harder than most basic techniques, and perhaps easier than many. I'd expect someone with a genin's understanding of ninjutsu to be able to make any clones at all within a day, but that understanding can take months to years to obtain. For children, at least; I'm unsure if adults would learn slower, quicker, or not at all."

"Nobody typically starts in adulthood? Why, if there's no reason to think children are necessarily faster?"

"Imagine someone who is bound, so they can only move very little, and very incidentally, from the moment of their birth. Perhaps at one year of age those bindings are removed. Perhaps at seven."

"If those bindings were left on for twenty-one years, would you expect someone to be able to learn to walk, let alone run?"

"It's not impossible to teach adults, but it is difficult and sometimes dangerous."

"...so people have, what, chakra atrophy? Some analogue of lack of muscle memory?"

"Both of those. Additionally, one of the standard biological processes in natives handles growing chakra capacity. If you never grow your capacity, this process stops on its own. Capacity growth isn't identical to the way muscles grow in strength, but some consider it analogous."

"Huh. What are the points of disanalogy?"

"You can't injure your chakra stores, though if you run too low you might separately suffer from chakra exhaustion. This does mean there's nothing directly analogous to picking up too large a weight. Chakra doesn't need to be used directly to grow. Exercising the body will increase yang chakra, and exercising the mind will increase yin chakra, though if someone isn't actively using their chakra while doing this there is - something like recoil."

"Running low on chakra is more like running low on blood than like exhausting your muscles, though the exact effects are different for yin and yang chakra. A lack of yang chakra leads to physical exhaustion, low temperatures, weakened immune systems, and difficulty coordinating muscles. A lack of yin chakra leads to depression, lack of executive function, and difficulty thinking."

"...there's recoil if people go for a jog or play strategy games while they do not actively do chakra stuff? Seriously? And is this low relative to whatever trained expanded amount, or low in an objective sense - with blood it's relative to body size and stuff, but -"

"The recoil isn't instantaneous, but most shinobi do use chakra every day, which is partially to avoid that. And chakra exhaustion happens at an objective amount, not as some percent of your current capacity. Someone with a high capacity and someone with a low capacity will suffer exhaustion at roughly the same absolute point. There's some variation in where that absolute point is, but in my time not enough research had been done to say why."

"But regular people around here have chakra too, right, and must sometimes jog or play chess."

"Yes. The recoil is in the fact that chakra capacity will grow a little, then return to prior levels, like an artery at a specific point. Most everyone does have day-to-day fluctuations in their capacity, though this is mostly notable in those with small capacities. The process of expanding and recoiling wasn't what I was referring to for stopping growth - it's the way chakra capacity can remain expanded that seems to shut down, roughly around the same time physical growth stops. A very rough analogy is like if exercising actually could increase your body size and blood volume. I apologize for being unclear."

"Exercising can do that if you add enough muscle mass!"

"Point. I apparently need better analogies."

"So assuming I don't have zero chakra I probably have infinity chakra because I have infinity stamina - I can get a little tired, a little hungry, etcetera, but not very much, it just sort of stops at 'noticeable but not particularly impairing'."

"That does seem reasonable, and is something possible - I now have infinite chakra myself."

"The first exercise is trying to feel chakra. It's difficult to identify within yourself without knowing what to look for, so the usual way to do this is I would pass my own chakra through your hands, and you would try to feel what I'm doing."

Cam holds out his hands.

Tobirama directs things so that Cam's hands are placed together, and Tobirama's are bracketing them. 

And that is a very weird feeling! It is distinctly confined just to Cam's hands. Kind of like if his blood had somebody else's blood swooshing on by at weird non-euclidean angles, and kind of like if somebody ran electricity through his hands except not even slightly painful.

"Gosh that's weird."

"Your own chakra will feel a bit different to you." He retracts his hands, and the weird feeling stops. Except maybe there's a tingle in Cam's hands still?

"Getting some aftereffect... not sure how to do anything with it."

He describes the process of trying to move that around, or produce it elsewhere - which for most people is more visualization than anything.

Cam gamely attempts to generate chakra-weird-feeling in more places!

This is actually fairly easy. Ish. It's easiest in hands and feet than in his torso, easier near the surface than deep down, and easier as a barely noticeable buzz than as anything that definitely isn't just his mind being really imaginative. 

"The next step is usually manipulating a piece of paper or leaf without touching it. It's easier to use chakra in your hands, so most will place a leaf on their palm, and attempt to push it away. Some find that causing the leaf to stick to them is easier. I've heard of traditions that use sand or water, as well, but haven't worked with them for students."

Cam materializes a leaf and sees if he can waft it up with a naive application of buzzy stuff.