Since most human movement is aimed at maximizing angular displacement of a distal segment through space, the use of 3rd class levers for is very efficient. A small arc of motion proximally at the muscle insertion will create large angular displacement and velocity distally. The opposite is true when you consider the distal lever displacement. However, this only holds true in terms of resistance. It may seem confusing that most of the muscles in the human body are 3rd class levers, since these levers are at a mechanical disadvantage in terms of effort versus load. With this type of leverage the muscles would be acting concentrically, as long as the distal lever is free.Īn example of this type of lever system is the biceps brachii acting concentrically on the forearm. Most muscles in the human body are 3rd class levers and create rotation of the distal segment. Classic examples are a seesaw or crowbar.ģrd Class Lever 3rd Class Levers in the Human Body The fulcrum is located between the applied force and the load. It’s important not to confuse this with moment and torque, which will be discussed in the next post. The location of these 3 components determines the mechanical advantage and the lever class. This can be achieved by calculating the distance between the axis and the where the force acts.
In assessing the efficiency of the lever (mechanical advantage), it is important to identify and quantify the components included in the system. Mechanical advantage can be calculated by dividing the effort arm by the resistance arm ( MA = EA/RA). The greater the mechanical advantage, the less effort required. The efficiency of the lever is called mechanical advantage (MA). A lever is a rigid object that is used with an axis to either multiply the mechanical force (effort) or resistance force (load) applied to it.
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