Apparently, if you can stand on one leg for ten seconds, then your likelihood of surviving the next few years is pretty good. I do a stretching routine that includes a one-legged yoga pose. I can hold it most days. If I am on squishy mat or something, it is harder. I don’t know what the significance of that is. In the fascinating Mexican movie Roma, in which some leader of hooligans gets the boys to stand on one leg with his arms up in a Y, which is supposed to mean something. The female protagonist could also do it.