Apparently it is a variant of saying 通臂拳, a kind of martial arts popular in the vicinity of Hebei. 通臂 (lit. through arm) refers to the fact that the qi or strength from the back of the practitioner can be delivered across the limbs.
This technique is also an imitation of the ape (猿), hence the name. The literature says the first traceable practitioner in history was Qi Xin 祁信 who lived in Hebei during the Qing Dynasty.