Extract from Sun Lutang. DISCUSSING DISTINCTIONS BETWEEN THE INTERNAL & EXTERNAL SCHOOLS OF MARTIAL ARTS (1929) translated by Paul Brennan:
余曰:「然則鄙人可謂得拳中之內勁乎?蓋氣已下沉,小腹亦堅硬如石矣。」
宗先生曰:「否!否!汝雖氣通小腹,若不化堅,終必為累,非上乘也。」余又問何以化之?
I said: “All that being the case, can I say I’ve obtained the internal power of boxing arts? My energy has sunk down and my lower abdomen is hard as a rock.”
Song said: “Oh, no no no. Even though energy might be getting through to your lower abdomen, if it doesn’t transform that hardness, it’ll eventually just make you feel overworked, and that isn’t the highest level.”
A misconception of breathe down to the Dantian?