The Yang Heel Vessel, Yangqiao Mai, is one half of a functional pair that classical Chinese medicine assigns joint responsibility for the body's waking and sleeping rhythm. Running up the outside of the leg to the eye, the Yang Heel Vessel is said to become dominant while a person is awake and physically active, governing the smooth movement of the legs during that state and taking a role in the eye's opening.
The "heel" in its name reflects its point of origin at the outer ankle, from which its course rises along the outside of the leg, a path that places it on the same lateral, yang-associated aspect of the limb that other yang channels typically follow, distinguishing its route clearly from its inner-leg, yin partner.
The character rendered heel in the vessel's name, qiao, also carries a sense of raising up and of nimbleness, and both readings appear in the classical literature, so the name does double duty: it locates the vessel at the ankle and it names what the vessel is for, the lifting and swift movement of the leg.
In the confluent point system the Yang Heel Vessel is opened at Bladder 62 below the outer ankle and paired with Small Intestine 3 on the hand. The Classic of Difficulties is among the early texts that treat the eight extraordinary vessels as a group with a logic of their own rather than as an appendix to the twelve regular channels, and its account of the Heel Vessels is one of the earliest systematic descriptions to survive.