Here, we're gonna talk about levers and levers are in your textbook in the muscle section. And there's a decent chance there's gonna be a question on levers in your test. But to me, really understanding how levers works really helps you understand how the body moves. Typically, when we think of levers, we're thinking about moving something that's heavy and a lever can make it easier to do that. Now that happens in the body sometimes. But another thing that levers do is that if you b build a lever differently, you can make things move really fast. And that's often how the body is using levers. The example I like to use is that there are human beings that can throw a baseball 100 MPH. That means their fingertips have to be moving at least that fast. There are no muscles in the body that can contract at 100 MPH. So how do they do it? They use a system of levers? All right. So let's see how this works. We're gonna say that muscles generate force using lever systems and a lever system is gonna be a rigid rod and in the body that's just a bone and there's a pivot point into the body that's a joint. And there's gonna be three aspects of leverage. We need to le learn here. There's gonna be the load and the load is gonna be the weight that has to be moved. And usually this is the body weight. But an example of the baseball, it might be, you know, moving the baseball as well. There's gonna be a fulcrum that fulcrum is the pivot point. And we already said in the body that's gonna be a joint. And then finally, there's going to be the effort and this is the force that's going to be applied to that rigid rod. And we are gonna say that this force is going to be applied at the insertion of a muscle. So we're gonna look at different joints here and think about what types of levers these are when you're thinking about where the effort is applied. Don't always look, where is the muscle? Look where the muscle inserts. All right, there's three types of levers. Here are first class, second class and third class lovers. And I'm gonna introduce a little mnemonic device that will build out in your, you'll understand where it comes from in a second. Our mnemonic device for 1st, 2nd and 3rd class lovers is that the Eiffel Tower had an Elf but he fell. It's kind of sad actually. All right, a first class lever. This is our Eiffel Tower. And this is the type of lever that you probably think of. When you think of a lever, when we did distinguish these different levers, we're gonna be talking about what order that load fulcrum and effort are in. So here we have an image of a person sort of pulling down on the rod, then comes the fulcrum and the load is on the other side. So we are going to say that we have the effort, the fulcrum and the load in that order, that's where our Eiffel Tower comes from. All right. Again, this is the lever that you're probably most familiar with the second class lever. We're gonna change the order here and you can see that we have the person way out on the end, applying the effort to the end of this rod in the middle is the load and the full crumbs on the other end. So we are gonna put this one in the order of elf effort load frum. That's our l. Now, you might not recognize this as a lever or think when does this happen. But this is how a wheelbarrow works, right? If we just sort of draw a wheel on here and a bucket, you can imagine that's a wheelbarrow. And I don't know about you. Sometimes I put a lot, lot of rocks in a wheelbarrow and it's pretty easy to lift the wheelbarrow on my end because I have the, the lever to help me our third class lever. We're gonna change the order again. We're gonna put the fulcrum on one end. We're gonna put the force in the middle and we're going to put the load on the end. This is the fell, the ll. So we're gonna put here the fel Fulcrum effort load. And you might look at that and you say, well, that looks like it's gonna make it hard to lift the thing, right? If this load is way out the end, that looks like it's gonna be hard and you're right, it is going to be harder. So why would you do something like this? Well, this is how a catapult works, right? You put the, you put a ton of force near the fulcrum and you can get this load out at the end moving really fast. All right. So let's look at where these happen in the body. So that when you're learning the muscles, you can sort of think what type of lever system is happening here. And, and how does that affect movement as we do this? We're gonna talk about mechanical advantage and disadvantage and an advantage means that it's gonna be easier to do the movement based on the structure of the lever. And a disadvantage means that it's gonna be harder to do the movement based on the the construction of the lever. So a first class lover, first class lover, a classic example of this is your head we have the, the muscle here, the sp funniest capitis and that uh has an insertion on the back of the head. When it contracts, that effort is going to sort of pull down on the head like that with the fulcrum in the middle and then the load is the head. So the, the load is pulling down here and it's gonna move this way. The advantage how easy it is to do a movement with a first class lever. Well, it's gonna depend on the location of the fulcrum. You can see in this example up here, the fulcrum is very close to the load. So you can imagine it's gonna be relatively easy for this person to pull down and move that rock in this image. But if we drew a different fulcrum, if we drew the fulcrum way up here right now, the fulcrum is very close to the effort. You can imagine that's gonna be very hard. That's gonna create a mechanical disadvantage for the person. OK. A second class lover. Classic example of a second class lever in the body is your calf muscle. The calf muscle is gonna pull up on your heel. The load is sort of in the middle, your body weight sort of centered over your foot. And the fulcrum is out here over the toe. This creates a mechanical advantage. And remember I said that's like the wheelbarrow, I can put a lot of rocks in my wheelbarrow and it's still easy for me to get them off the ground and wheel them around because I'm working at that mechanical advantage. Our third class lover system, this is how a lot of the muscles and the arms and the legs work and a third class lover system we talked about sort of like that catapult. It's gonna work at a mechanical disadvantage. And we can see that here with the biceps brachii, the insertion is there on the forearm. The fulcrum is at the elbow. So that insertion is really close to that fulcrum. And the weight that you're trying to move this weight, maybe throwing a baseball is way out there at the end, that means that this muscle has to work really hard to move that weight. All right. So just to sort of formalize our talk about advantage and disadvantage, we're gonna say that advantage is determined by the location of the fulcrum. If the fulcrum is closer to the load, that is going to equal an advantage. If the fulcrum is closer to the effort, that's gonna equal a disadvantage. Ok. So why would you want to work at a disadvantage? Well, a mechanical disadvantage. Yes, it requires more effort to do the movement, but it, it creates a greater range of motion. You can throw a baseball 100 MPH because your body is working as a series of levers in series all working at a mechanical disadvantage. You're moving your shoulder you're moving your upper arm, you're moving your forearm, you're moving your hand, you're moving your fingers all at mechanical disadvantages. That means you need to put a ton of force into it, which is why pitchers often injure their arms. But in doing that, you can move that baseball, the tips of your fingers very, very fast. All right. Again, you may get some questions about levers on a test, but understanding how levers work will really help you understand how the body moves. That there's an example of following practice problems after that. Give them a try.
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example
Levers Example 1
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This tells me that the origins for the three hamstring muscles are on the ischial tuberosity. The insertions are on the proximal end of the tibia and the fibula. And it says, knowing this, what type of lever system is the hamstring a part of when it performs the movement of flexing the knee, then it wants to know would you expect the hamstring to work at a mechanical advantage or disadvantage when it performs this movement and to guide us a little bit, it has an image of somebody flexing their knee, bending their knee backwards like that. And it shows us one of those muscles, the hamstring, that's the biceps for Morris. All right. So to figure out the lever system, I wanna look at this muscle and the biceps for Morris has its origin upon the issue tuberosity. It also has an origin on the back of the femur there. But that's not gonna change anything about this problem. And it has an insertion on the proximal end of the tibia and the fibula right there. Now, to figure out my lever system, I need to find the fulcrum, the effort and the load. So let's start with the fulcrum, the fulcrum, we said is the pivot point. So the pivot point for this movement, it's gonna be the knee. So I'm just gonna put a point there and put an f, that's my fulcrum. All right. Next, let's think about the load. Where is the weight that this is moving? Well, the weight is in the leg, it's, you know, somewhere out here is gonna be the center of gravity of the leg, something like that. So this is gonna be my load. So then the question is, where's the effort? Well, we said you find the effort by finding the insertion or the muscle that's doing the movement. So my insertions right here. So I'm gonna put effort sort of right there at that proximal end of the tibia and the fibula. So as I look at this and now I try to remember what lever system is this. I can remember my mnemonic device, the Eiffel Tower had an Elf but he fell and I look what does this spell out? It spells out left. That wasn't one of my options. But if I read it the other way it spells out fell. The Eiffel Tower had an elf but he fell. This is a third class lover system. In a third class lever system. The effort is between the fulcrum and the load. So does a third class lever work at a mechanical advantage or disadvantage? Remember, a mechanical advantage means the lever makes it. So there's less effort needed to move the load. Mechanical disadvantage means that you have to put in more effort to move the load. So what does a third class lover do? Third class lover works at a disadvantage? So we said that the whatever is closer to the fulcrum tells you your advantage or disadvantage here, the effort is closer to the fulcrum. So that means it's gonna be take a lot of effort to move this load. So why is this muscle arranged this way to make it take more effort? Well, remember the benefit of third class lovers is that the end of this rod here where the load is, is gonna move really fast and have a large range of motion. So if you wanna run fast, you want your legs to have third class levers in them. And this is why so many of the muscles of the arms and the legs work as third class lovers.
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Problem
Problem
In what type of lever is the force applied between the fulcrum and the load?
A
First-class.
B
Third-class.
C
Second-class.
D
Force cannot be applied between the fulcrum and the load.
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Problem
Problem
The majority of the lever systems in the arms and legs are third-class levers; there are few second-class levers. Knowing this which of the following statements is correct?
A
The muscles of the arms and legs usually work at a mechanical disadvantage.
B
These joints will have relatively small range of motion.
C
Most movements of the arms and legs prioritize power over speed.
D
The fulcrum will most often be placed between the effort and the load.