I’m curious how or if that affects physical training, like gymnastics or martial arts.

No, they don't magically have some sense of north. They're just used to using it so much that they have a lot of points of reference to know which direction is which no matter where they are.

Not necessarily just a sense of reference, but also a practice of always keeping in mind what direction one is when changing direction (mentally summing up the deltas in direction).

I do this when driving - I always know what direction I'm headed, even in an unfamiliar place (unless there are a ton of non-right-angle turns that confuse me, and then I have to check a map).

It's just a succinct abstraction.

Blocking a punch or doing a kata also has no concept of north. It's usually bilateral. So if you don't have left or right... Do you pretend your face is north and instruct that way?

I'm not sure what you mean. Whichever way you happen to be facing, you can use an earth-relative coordinate system to disambiguate limbs rather than a person-relative one. I guess don't practice martial arts while standing on the north or south pole and you'll be fine.

How do you explain throwing or joint-locking an opponent to someone who does not believe they have a right or a left arm? Both of these actions can involve turning around. Anywhere from 45º to 360º.

Here's a long passage from the article that sheds a little bit of light on it. My assumption before reading it was that even if they don't use egocentric coordinates, they would still have a concept of "left hand" and "right hand" as permanent objects, since they're not identical (people usually have a dominant hand). Now I'm not so sure!

> When these peculiarities of Guugu Yimithirr were uncovered, they inspired a large-scale research project into the language of space. And as it happens, Guugu Yimithirr is not a freak occurrence; languages that rely primarily on geographical coordinates are scattered around the world, from Polynesia to Mexico, from Namibia to Bali. For us, it might seem the height of absurdity for a dance teacher to say, “Now raise your north hand and move your south leg eastward.” But the joke would be lost on some: the Canadian-American musicologist Colin McPhee, who spent several years on Bali in the 1930s, recalls a young boy who showed great talent for dancing. As there was no instructor in the child’s village, McPhee arranged for him to stay with a teacher in a different village. But when he came to check on the boy’s progress after a few days, he found the boy dejected and the teacher exasperated. It was impossible to teach the boy anything, because he simply did not understand any of the instructions. When told to take “three steps east” or “bend southwest,” he didn’t know what to do. The boy would not have had the least trouble with these directions in his own village, but because the landscape in the new village was entirely unfamiliar, he became disoriented and confused. Why didn’t the teacher use different instructions? He would probably have replied that saying “take three steps forward” or “bend backward” would be the height of absurdity.

Others do not have language for absolute directions. The Murrinhpatha in Australia. https://www.degruyter.com/document/doi/10.1515/opli-2016-000... I think the Pirahã may only use directions relative to the river