“Borrowed force” is the term American Kenpo Karate uses to refer to a martial arts principle (other martial arts use it but might call it something else). So what does it mean? In short, just what it says: It is power that doesn’t belong to me, but I can use it. The catch is: I can use it IF I am quick enough and my timing is right. This is a tricky thing to explain in words without being able to show someone, but I’ll give it a shot.
I can think of several Kenpo techniques right now from lower belt ranks that use this principle. I should say, the technique provides an opportunity to take advantage of borrowed force. The technique still works if you miss this opportunity, but it is less devastatingly effective. If a standard defense and counter-attack are timed as “one, two” in beats, then taking advantage of borrowed force usually means counter attacking on the half- or even quarter-beat. Borrowed force takes advantage of the attacker’s momentum. It’s usually forward momentum (toward you), but it could be sideways, up or down…
Let me use this example: Your strike meets their bodily momentum like two cars crashing at 60 mph each and causing a 120 mph impact. If you’re going 60 and they are only going 30, then you have a 90 mph impact. But the real point is: If you’re going 60 mph, and they have stopped moving, then there is no borrowed force to take advantage of. This is why getting the counter-attack in on the half- or quarter-beat is important. This is easier with hands than feet. Arms are simply lighter and more coordinated than legs, so it’s easier to move them more quickly and precisely. But techniques like Thrusting Salute and Intellectual Departure do use borrowed force with kicks.
Let’s take Attacking Mace as an example. The attacker throws a right straight punch. You deflect the punch with a left thrusting block, crossing diagonally. Bonus if your left knuckles meet his face, but that may or may not work out. A fraction of a second later, your right fist smashes into the attacker’s ribs under his right armpit like a battering ram. A fraction of a second because you want to catch him while he is still moving forward and has not settled his weight yet.
I can tell you from personal experience that it’s very painful to get punched in the armpit, where all those nerves are. In fact, just pressing my own fingertips into my top ribs right under the armpit is downright uncomfortable. Now, if all the bones from the shoulder joint to the elbow to the wrist to the first knuckles are lined up, then you have backup mass and structural reinforcement. If you drop your weight slightly at the right time, you get “marriage of gravity” (a topic for another post). If you rotate your right hip forward, you get extra power from torque without moving your feet or your center much. Now take all that power generated by proper techique and add the force of the attacker running into your battering ram.
The rest of Attacking Mace calls for hyperextending the attacker’s elbow with an upward left palm strike, a right kick to the stomach or groin (take what you can get), a right leg check to prevent a successful counter-attack, and a left punch to the lower, back ribs. But I think you’d probably only need all that if you missed that first blast to the underarm ribs. Done right, it could literally knock someone off their feet. I noticed that many Kenpo techniques include devastating and highly effective moves at their beginnings, and all the moves in the sequence after seem like overkill. But my instructor said that it’s NOT “overkill”, it’s “over skill”, and that Kenpo does not take anything for granted.