This term is easily translated as ‘power off’. Other words in English referring to nuki could be without; not including; dispensed with, thus it’s like a piece of electricity. Energy flows through the wires until the plug is pulled. Suddenly the energy disappears. A moment of kime at impact (energy transfer) is like the pulse of a heartbeat. We use this idea in Wado technique. By using nuki you leave all potential energy in the opponent. This is not the same as withdrawing the fist after impact.
Another function of nuki is to move without effort.
Hiza no nuki 膝の抜き
This means to unblock the knee. Actually it is how to use the knees and ankles to facilitate correct movement. The objective of hiza no nuki is to bend the knee(s), move smoothly and use the gravity pulling the whole body forward. Nuki means to cut off the power, or in this cause to drop the tension or unblock the knee(s). You should tense some muscles to remain in kamae, else your body will collapse.
Use the hiza no nuki to move forward without resistance and use the gravity to accelerate movement. If you remain tensed you will have more trouble accelerating, overcome inertia.
For example in junzuki, when you use hiza no nuki, the center is driven forward from tanden and the gravity is pulling the body forward. The ankle of the supporting leg will tighten during ukimi (floating body) naturally. Unnecessary tension should be avoided.
Take care, bending caused by bending is a common error, you should bend by unblocking.
On the video below im standing on my tiptoes on purpose, to extend my knees and ankles completely, in order to unblock them instantly later on.
PRINCIPLES