Personal Training 2: skeletal anatomy: understanding levers

Skeletal anatomy is part of the personal training course that I am studying for at the moment.  Skeletal anatomy is often considered to be the poor relation of its sexier cousin, muscular anatomy, because it doesn’t actually do anything, it just sits around getting moved by the muscles.

Despite this, there is so much to say about the different skeletal bones because of where the muscles are attached to them and how they join together at the joints.  In fact, it is the exact location of the attachments that specifies the true actions of muscles more than anything else.

However, before we can think about the individual skeletal bones, the points of muscular attachment and the way that they joints are made up, we need to understand the theory behind levers.

Why is understanding levers important?  Well levers are what enable muscles to effect movement.  And how many times have you heard someone say “well, he doesn’t have good leverage from that position”?  That’s a comment about how good the lever is.  Levers are important.

To understand how good (or bad) our levers are and how we can influence them, we need to know what makes a good lever and what makes a bad lever (sorry for the bad finance joke!).  And to that end, we need to understand the secret of levers…

***

The secret of levers

There are three classes of levers.  Each class of lever is defined according to where the fulcrum, the load and the force are placed with respect to each other.  The different classes of lever are more or less effective at moving weight.

In fact, class three levers, the weakest, are less effective than moving the weight without a lever at all…

***

Class one lever

I drew the following picture for you to show you the effect of a class one lever.  (Honestly, I drew this just for this post.  I didn’t nick it from anyone else).  The fulcrum (the triangle) is situated between the applied force and the resulting force, or load to be moved.  Real-life examples of class one levers are crowbars and scissors.  Class one levers are very effective at increasing the force you can apply.

The human skeleton uses a class one lever to move the skull on the top cervical vertebra.  The posterior neck muscles pull the skull back on the fulcrum of the vertebra and cause the load, which sits in front of the vertebra, backwards into extension.

Class one lever: classy

***

Class two lever

I drew the following picture for you to show you the effect of a class two lever.  (Hey, I’ve been busy working on this stuff!)  The load, or the force to be generated, sits between the applied force and the fulcrum (the triangle).  This makes for a less effective lever.  The most common real-life examples of class two levers are wheelbarrows and nutcrackers.

The human skeleton uses a class two lever to create plantar flexion against resistance.  With the toes on a step, the calf muscles pull on the heel, which elevates the load (the centre of mass of the body), which sits between the heel and the step.

 Class two lever: less classy

***

Class three lever

I drew the following picture for you to show you the effect of a class three lever.  (I was doing a lot of drawing that day!)  The applied force sits between the load and the fulcrum (the triangle).  This makes for a much less effective lever.  In fact, this lever is less effective than applying a direct force!  The most common real-life examples of class three levers are tweezers.

The human skeleton uses class three levers frequently.  The most obvious example is to flex the arm at the elbow.  The biceps muscle pulls on the radius, which sits closer to the weight (held in the hand) than the fulcrum of the elbow.

Class three lever: not very classy at all

***

Summary

OK, so I admit it, it’s still not as sexy as muscular anatomy but hopefully this short post goes a little way towards defending the importance of skeletal anatomy in understanding the way the human body moves.