PRE-LABORATORY ACTIVITIES 1. Study the lever systems in the textbook and sketch

Question

PRE-LABORATORY ACTIVITIES 1. Study the lever systems in the textbook and sketch an example of each system in the space below labeling weight, fulcrum and force. Using the lever systems available in the laboratory, demonstrate each class of lever. Determine the advantage gained or lost by repositioning fulcrum, effort, or resistance. Perform various single movements of your body parts and attempt to determine the class of lever involved. Which class of lever is most common in your body? Write a description of the way each of the three lever systems works. Fulcrum Force Fulcnam 11.1 Practical Lecturel

Explanation / Answer

We can consider the mechanisms by which muscles act on bones using descriptions based on levers. A lever is a rigid structure, in this case, a bone, that moves on a fixed point called the fulcrum, in this case, an articulation. A lever moves when an applied force or effort is sufficient to overcome any load or resistance that would otherwise oppose or prevent such movement. In the body, each bone is a lever and each joint is a fulcrum, and muscles supply the applied forces. Movement of the skeleton occurs at joints, so there has to be sufficient muscle power to move all the bones at these joints.

Levers can change the direction and effective strength of a force as well as the distance and speed of movement produced by the force. Imagine a seesaw in a playground. You and a friend could sit on opposite ends of it. You would then take turns pushing off the ground with your legs as you each went up in the air. A seesaw is an example of a first-class lever, and there are three classes of levers. The fulcrum (F) lies at the midpoint of the seesaw, between the applied force (AF) and the load (L). What this means is that the seesaw balances you and your friend, as you both provide the applied force with the push of your legs and the load with the weight of your bodies.

The body has only a few first-class levers. One is involved in head flexion (pulling the head down toward the chest) and head extension (pulling the head back up into normal position). The fulcrum is where the head moves in the sagittal plane on the first cervical vertebrae. The load is the weight of the head, and the applied force comes from the muscles. Extension occurs when the muscles pull the head back up. Moving your head forward and backward mirrors the action of a seesaw.

In a second-class lever, the load is located between the applied force and the fulcrum. When you move a load in a wheelbarrow, you lift upward on the handle and the wheel acts as the fulcrum. The force is further from the fulcrum than the load is, so you can move a larger weight with less effort. In the body, you achieve the same effect by standing on your toes. The fulcrum is on the ball of the foot, the load is your body weight, and the effort comes from the muscles in the back of the leg.

In third-class levers, the force is applied between the load and the fulcrum. We don’t often see these types of levers in artificial machines, but they are the most common levers in the body. Speed and distance travelled are increased at the expense of force. For the biceps brachii in the arm, the load will be located in or around the hand. The biceps muscle applies the force, while the fulcrum is the elbow. For instance, when you pick up a full bag of groceries, you can lift it quickly using the third-class lever of the biceps brachii and the forearm. However, the location of fulcrum prevents great enhancements of load carrying.
The third class lever is most common in the human body. An arm is an example of a third-class lever. The elbow area is the Fulcrum, the upper arm muscle acts as the force, and the load will be located in the hand, which could be used to lift, push, or grab.

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