Levers

There are a great many different levers at work in the martial arts. Your bones form levers, as do weapons. It is worth spending some time discussing levers so you have a fundamental understanding of how they work and how you can use them to your advantage.

We will use the diagram at the top of this post for some of our discussion. There are two distances we will want to reference often. The first is the distance between points A and B. We will refer to this distance as AB. The second of course is the distance from B to C, which we will call BC.

The blue triangle at point B represents a fulcrum. The fulcrum is the place at which the lever is supported and pivots. We will also at times discuss various masses or weights located at points A and C. We will refer to these masses as MA and MC respectively.

Levers are often used to lift heavy objects. If a weight is placed at position A, then applying a downward force at position C will lift the object with a mechanical advantage. The object will be easier to lift than if you tried to pick it up manually.

A lever will be perfectly balanced with a mass at both Point A and Point C if the following is true:

MA * AB = MC * BC

Because this is a multiplicative factor, it takes less weight at point C to balance the weight at point A (provided that distance BC is greater than distance AB). If the BC distance were to be increased further, then it would take a smaller mass MC to balance the lever.

Let’s examine a simple example. Assume that MA is 100 lbs. and that the distance AB is 4 feet. We will also say that distance BC is 8 feet. This means the product MA * AB is 400. In order for the two sides to be balanced the right side of the equation must be MC * 8 = 400. Clearly MC must be 50. So it therefore takes 50 lbs of downward pressure or weight at Point C to balance 100 lbs positioned at point A.

If the BC length is increased to 12 feet, then the formula MC * 12 = 400 means that now only 33.3 lbs. of force need be applied at Point C to balance MA.

Of course, moving the fulcrum closer to point A changes things as well. Let’s say the fulcrum moves so that AB is now 2 feet. We will again assume that BC is 8 feet and that MA is 100 lbs.

Our formula is now:

2 * 100 = 8 * MC, or

200 = 8 * MC

MC must now be 25 pounds (200 divided by 8).

While this last lever arrangement can lift more weight (giving it greater mechanical advantage) it will do so more slowly or over a smaller distance than the earlier levers.

Let’s consider inverting where we apply force. Assume that we apply a downward force to Point A rather than Point C. Now it takes greater effort to lift a load, but the movement will be much faster and will move a greater distance. This is something to consider and we cover it in more detail on the post regarding Angular and Tangential Velocities.

There are three different types or classes of levers. These include:

  1. First Class Lever:  This class of lever has the fulcrum located somewhere other than at one end.  It may be used for mechanical advantage to magnify force, or at a mechanical disadvantage to increase speed and movement distance, in which case the force and load reverse positions.
  2. Second Class Lever: In a second class lever the fulcrum is located at one end and the force is applied at the other. The load is located somewhere between the fulcrum and the point of force application. These levers offer strong mechanical advantage but limited movement and speed.
  3. Third Class Lever: In this lever arrangement the fulcrum is at one end and the load is at the other. The force is then applied to some location between these two points. These levers operate at a mechanical disadvantage. They offer fast and large movements but suffer from a lack of strength.

In the human body the bones associated with motion or movement function as levers. Muscles attached to the bones (at what is referred to as the muscle insertion point) apply the required force or effort. The load can be simply the weight of the body parts being moved or might include a weight such as something carried in the hand. The fulcrum is commonly a joint.

The most commonly cited example of a lever in the human body is the forearm. The biceps attach to the radius bone in the forearm, but not far from the elbow joint. When the biceps contract the forearm functions as a third class lever. The forearm, hand, and whatever the hand is holding comprise the load. The elbow joint functions as the fulcrum.

This means the biceps are not intended nor best used for strength, though this is how most people think of these muscles. The primary purpose of the biceps is to provide rapid large movements to the forearm. Because of this mechanical arrangement the biceps work best with the arm is already somewhat bent. You can see this when you think of lifting a heavy load. Consider how much more difficult it is to lift the load if your arm is straight rather than already bent. The mechanical arrangement of this lever should explain why this occurs. This also explains why it is best to keep your arms located within your center triangle and why blocks are strongest when the arm is bent near 60°.

It turns out that most locomotion (long bone) levers in the body are third class levers. The muscle insertion point is usually not far from the joint (fulcrum).

There are very few second class levers in the body. The joints in the balls of the feet function as a fulcrum when you raise up onto your toes. This arrangement functions as a second class lever. However, if you simply wiggle your toes, then these joints are part of the levers that move the toes. This works because different muscles and joints associated with the ball of the foot are being employed in the two different types of levers.

The fingers of the hand are quite complex and utilize all three lever classes. When you squeeze your grip tightly you are employing a powerful class one lever. When you extend your fingers you employ a type two lever, which explains why this is not as powerful as your squeezing strength. The pinching action utilizes a third class lever which explains why the motion is quick and precise, but not particularly strong.

Nodding employs a first class lever. Your head sits atop your spinal column, which functions as the fulcrum. So the fulcrum is not at one end, making this joint the fulcrum of a first class lever. Muscles then pull the head forward and back about this fulcrum to enable you to raise and lower your head.

You will note that most bones in the arms and legs are arranged as class three levers. This means your extremities are primarily designed for speed and large ranges of motion. This is why speed is often more useful and effective than power in the martial arts.

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