Human body levers

[cookbeat01]

I know the human body is mostly third class levers, making it operate at a mechanical disadvantage. What would happen if the human body were made of first or second class levers?

[Rebiu]

I know the human body is mostly third class levers, making it operate at a mechanical disadvantage. What would happen if the human body were made of first or second class levers?

You are mistaken my friend. Every joint creates a first and third class lever. The bending of the joint is the third class lever and the extension is the first class lever.

 

Second class levers can be created with the body. We use them all the time in wrestling and Brazilian Jiu Jitsu.

[Neil9327]

Well if I had some first class levers in me I'd be able to open a bottle of beer and crack some nuts without having to use a tool...

[Mokele]

I guess I'll resurrect this thread to give a good answer:

 

The human body is actually mostly 1st and 3rd class levers. Consider your elbow. Hold your upper arm against your body, and bend your elbow 90 degrees. Your triceps is acting as a 1st class lever (the in and out forces are on opposite sides of the fulcrum), while your biceps is a 3rd-class lever (the forces are on the same size, with the muscular in-force closer to the fulcrum). A second-class lever in your body would be your jaw at the molars, which function just like a nutcracker.

 

The effects of switching to second-class levers would be increased force, but decreased range of motion.

 

However, there's a lot more to it than simple physics - anatomy and muscle physiology come into play. For instance, most muscles cross more than one joint (in the limbs, 2 joints is pretty typical), which means their function, when active, depends upon the function of other muscles around those joints. Your Biceps can function as an elbow flexor, an extremely weak shoulder protractor, and a suppinator (rotates the forearm), and which it does depends upon which other muscle are active, holding certain joints locked while allowing movement at others.

 

Muscle physiology comes in as the length-tension curve. Muscle can only change in length by about 30%; any more and they rip or just generate no force. More importantly, the force isn't constant. See the graph here at wikipedia. Beyond a narrow region of optimal length, the force a muscle can generate at maximal recruitment declines, often sharply. However, we can't simply assume where this region of optimum length is, because detailed experiments have shown that the combination of changing effective lever arms during contraction and changing length can result in optimum torque at an angle different from what would be predicted from either muscle physiology and lever arms alone.

 

So basically, it's very complex.