Learn about muscle lever systems in the body. Discover the types of levers in the body and which parts of the body act as levers. See examples of anatomical levers.
Updated: 02/18/2022
Muscle Levers in the Body Examples
Lever Systems in the Body
Lever systems in the human body are formed by muscles and bones, and the primary purpose or function of a lever system is to produce a mechanical advantage. A mechanical advantage refers to turning a small force into a larger force. A mechanical advantage can also involve turning a force into a large movement.
Skeletal Muscle Contraction
Skeletal muscles are attached to bone on each end by tendons. This attachment causes bones, and thus body parts, to move when our muscles contract. Furthermore, the nature of the attachment affects the efficiency of movement in terms of strength, speed and distance moved. Muscles work by way of lever systems which is a rigid lever, such as a bone, that moves on a fixed point called a fulcrum.
A teeter-totter is a good example of a lever system. The weight of each person on either side represent the force and load, while the pivot in the middle represents the fulcrum. If the fulcrum is in the middle of the board, two people with the same weight will balance the board.
Moving the board relative to the fulcrum will result in unbalance, making it easier for one person to push the other up. Just as moving the fulcrum of a teeter totter can increase the effectiveness of a force, the nature of muscle attachment to bone relative to the joint increases the efficiency of muscle contraction and thus, body movement. A lever moves when a force (F), or effort, is great enough to overcome a load (L), or resistance, that would otherwise resist movement. This lesson describes the three basic lever systems utilized by our muscles and bones for body support and movement.
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Which Parts of the Body Act as Levers?
Which parts of the body act as lever systems? The lever systems in the body consist of four primary parts. These four parts include:
- Lever: Levers, also known as anatomical levers, in the human body refer to a bone.
- Pivot/fulcrum: A pivot, also known as a fulcrum, refers to the joint that is formed by the connection between two or more bones.
- Effort: The effort refers to the force generated by the contraction of the muscles in the lever system.
- Load: The load, also known as resistance, refers to the weight or mass that is moved by a lever system.
For example, when a person lifts a cup of water to their mouth when drinking, their forearm is the lever, and their elbow is the pivot. The biceps brachii (muscle at the front of the upper arm) generates the force needed to lift the cup of water up to the mouth. The weight of the forearm and the weight of the glass of water is the load that is moved by this lever system.
Types of Levers in the Body
There are three primary types of levers in the body: first-class levers, second-class levers, and third-class levers. Each of these lever systems differ by the way the pivot (joint), load (weight of body), and effort (muscle contraction) are arranged. The following sections will provide information about each of these types of muscle levers in the human body.
First-Class Levers in the Body
First-class levers in the body occur when the pivot (joint) is located between the effort (muscles) and load (body weight). A first-class lever in the body is very similar to a seesaw. The pivot point of a seesaw is located between the effort (person pushing off the ground on one side) and load (weight of the person on the other end of the seesaw). Scissors are another example of a first-class lever.
An example of a first-class lever in the human body is the joint formed by the top of the vertebral column and skull, which is known as the atlanto-occipital joint. In this lever system, the skull is the lever, the atlanto-occipital joint is the pivot, the muscles at the back of the neck are the effort, and the weight of the skull is the load. The muscles at the back of the neck provide the force needed to move the head backwards, which is a movement known as neck extension.
First-class levers provide a mechanical advantage. In the example of the atlanto-occipital joint, a relatively small force generated by the neck muscles can move the comparatively heavier load of the head.
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Second-Class Levers in the Body
Second-class levers in the body occur when the load is between the effort and pivot, and it is very similar to a wheelbarrow. In a wheelbarrow, the pivot is at the wheel, the load is in the trey, and the effort is the force is generated by the person lifting the handles upward. Second-class levers are usually the most efficient at moving heavy loads with little effort or force.
An example of a second-class lever in the body is when a person is standing on their tip toes. In this lever system, the toes are the pivot, the weight of the person is the load, and the calf muscles are the effort. The calf muscle provides the force needed to lift the body upward at the point of the toes. This movement of the toes and ankle, to stand on the tip toes, is known as plantar flexion.
Second-class levers provide a mechanical advantage. In the example of a person standing on their tip toes, the relatively small force generated by the calf muscles can raise the comparatively heavier load of the entire body. In lever systems, strength is increased as the force is moved farther away from the load.
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Third-Class Levers in the Body
Third-class levers in the body occur when the effort is between the load and the pivot. An example of third-class lever is a person using a broom. In this situation, the hand near the top of the broom is the pivot, the lower hand is the effort, and the bottom of the broom that is sweeping the floor is the load.
Third class lever examples in the body include when the elbow is bending. The elbow joint is the pivot, the biceps brachii (which attaches to the forearm) is the effort, and the forearm and hand is the load. When the biceps brachii contracts, it provides the force needed to bend the elbow and raise the forearm and hand. This movement of bending the elbow is known as elbow flexion.
Third-class levers do not provide a mechanical advantage by turning a small force into a larger force. Rather, third-class levers provide a mechanical advantage by turning of force into large, fast movement. In the example of the elbow, a force generated by the biceps brachii can cause large and fast movements of the forearm and hand.
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The phrase FRE 123 can help a person remember the differences between first, second, and third-class levers. The ''F'' stands for fulcrum, the ''R'' stands for resistance, and the ''E'' stands for effort. FRE 123 represents which of these three parts is in the middle of the lever system. If the ''F'' is in the middle, it is a first-class lever. If the ''R'' is in the middle, it is a second-class lever. If the ''E'' is in the middle, it is a third-class lever.
Lesson Summary
Lever systems in the body are formed by muscles and bones. The purpose of lever systems is to provide a mechanical advantage, which involves turning a small force into a larger force or movement. There are four parts of a lever system in the body, which include a lever (bone), pivot/fulcrum (joint), effort (force generated by a muscle contraction), and load (weight moved by the lever). The strength of a lever system is increased as the force is moved farther away from the load.
There are three types of lever systems in the body, which include first-class levers, second-class levers, and third-class levers. First-class levers occur when the pivot/fulcrum is located between the effort and load, much like scissors. An example of a first-class lever in the body is the atlanto-occipital joint, which is formed by the connection between the spine and skull. The atlanto-occipital joint allows a person to perform neck extension. Second-class levers occur when the load is between the effort and pivot, much like a wheelbarrow. An example of a second-class lever in the body is a person standing on their tip toes, which is a movement known as plantar flexion. Second-class levers are usually the most efficient at moving heavy loads with little effort or force. Third-class levers occur when the effort is between the load and the pivot, much like a broom. Third-class lever examples in the body include a person bending their elbow, which is a movement known as elbow flexion . The phrase FRE 123 can help a person remember the differences between first, second, and third-class levers.
First-Class Lever
Let's take a look at first-class levers. While the body has relatively few first-class levers, they are easy to understand as they resemble a teeter-totter. In such a lever, the load is located on the opposite side of the fulcrum as the applied force.
For example, head extension is a good example of a first-class lever system. Here, neck and back muscles apply a force to move the head. The weight of the head is the load, and the fulcrum is the joint between the skull and the vertebrae.
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Second-Class Lever
Let's move on to second-class levers. In a second-class lever, the load is located between the force and the fulcrum. A wheel barrow is a great example of a second-class lever system. Here, the wheel is the fulcrum, or the pivot point, the weight is the load and lifting the handles applies the force to move the load.
What about in the body? Plantar flexion, or standing on balls of our feet, is an example of a second-class lever in the body. Here, the ball of the foot is the fulcrum, the weight of the body is the load, and the contraction of the calf muscles provides a lifting force, or effort. This type of system allows a small force to move a relatively large load. In fact, moving the force further away from the load increases the strength of the lever system. However, speed and distance of movement are compromised at the expense of this increased strength. In other words, a relatively small force moves a large load a relatively short distance and moves it slowly.
Third-Class Lever
Now let's talk about third-class levers. Third-class levers are the most common in the human body. Here, the force is applied between the load and the fulcrum. A broom is a good example of a third-class lever where the hand on top of the broom represents the fulcrum, or the pivot point. The force is applied in the middle of the broom by your other hand, which will then move the broom (the broom being the load).
An example of a third-class lever in the body is forearm flexion, where the elbow is the fulcrum, the biceps apply upward-directed force to the forearm. The load is the forearm itself and anything that may be held in the hand.
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The effect of third-class levers is the opposite of that of second-class levers. With third-class levers, speed and distance of load movement are increased, but at the expense of decreased strength. In other words, a large force is needed to move a relatively small load far and fast. In fact, the force required to move a load is increased the closer it is to the fulcrum. With forearm flexion, the load, or the weight in the hand, is six times further from the fulcrum than the applied force - that is, the biceps brachii attachment to the forearm. Therefore, the force must be six times as great as the load in order to move it. However, the load is moved far and fast.
Lesson Summary
In summary, body movement occurs when our muscles contract. Our muscles utilize three different lever systems to move our body. In the lever systems in the body, the fulcrum is the joint, the force is muscular contraction and the load is the weight of the body part moved. Head extension is an example of a first-class lever in which the load and force are on opposite sides of the fulcrum. Plantar flexion is a good example of a second-class lever in which the load is located between the applied force and fulcrum. Third-class levers are most common in the body; for example, forearm flexion, in which the applied force is between the load and the fulcrum. If you can remember FRE 123, you can remember what is in the middle of each lever. The fulcrum, beginning with 'F,' is in the middle of first-class levers, resistance, beginning with 'R,' is in the middle of second-class levers, and force, or effort, beginning with 'E,' is in the middle of third-class levers.
Learning Outcome
After viewing this lesson, students should be able to:
- Understand how our muscles work
- Define fulcrum, resistance and effort (FRE)
- Recall the three types of lever and how they work
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Video Transcript
Skeletal Muscle Contraction
Skeletal muscles are attached to bone on each end by tendons. This attachment causes bones, and thus body parts, to move when our muscles contract. Furthermore, the nature of the attachment affects the efficiency of movement in terms of strength, speed and distance moved. Muscles work by way of lever systems which is a rigid lever, such as a bone, that moves on a fixed point called a fulcrum.
A teeter-totter is a good example of a lever system. The weight of each person on either side represent the force and load, while the pivot in the middle represents the fulcrum. If the fulcrum is in the middle of the board, two people with the same weight will balance the board.
Moving the board relative to the fulcrum will result in unbalance, making it easier for one person to push the other up. Just as moving the fulcrum of a teeter totter can increase the effectiveness of a force, the nature of muscle attachment to bone relative to the joint increases the efficiency of muscle contraction and thus, body movement. A lever moves when a force (F), or effort, is great enough to overcome a load (L), or resistance, that would otherwise resist movement. This lesson describes the three basic lever systems utilized by our muscles and bones for body support and movement.
First-Class Lever
Let's take a look at first-class levers. While the body has relatively few first-class levers, they are easy to understand as they resemble a teeter-totter. In such a lever, the load is located on the opposite side of the fulcrum as the applied force.
For example, head extension is a good example of a first-class lever system. Here, neck and back muscles apply a force to move the head. The weight of the head is the load, and the fulcrum is the joint between the skull and the vertebrae.
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Second-Class Lever
Let's move on to second-class levers. In a second-class lever, the load is located between the force and the fulcrum. A wheel barrow is a great example of a second-class lever system. Here, the wheel is the fulcrum, or the pivot point, the weight is the load and lifting the handles applies the force to move the load.
What about in the body? Plantar flexion, or standing on balls of our feet, is an example of a second-class lever in the body. Here, the ball of the foot is the fulcrum, the weight of the body is the load, and the contraction of the calf muscles provides a lifting force, or effort. This type of system allows a small force to move a relatively large load. In fact, moving the force further away from the load increases the strength of the lever system. However, speed and distance of movement are compromised at the expense of this increased strength. In other words, a relatively small force moves a large load a relatively short distance and moves it slowly.
Third-Class Lever
Now let's talk about third-class levers. Third-class levers are the most common in the human body. Here, the force is applied between the load and the fulcrum. A broom is a good example of a third-class lever where the hand on top of the broom represents the fulcrum, or the pivot point. The force is applied in the middle of the broom by your other hand, which will then move the broom (the broom being the load).
An example of a third-class lever in the body is forearm flexion, where the elbow is the fulcrum, the biceps apply upward-directed force to the forearm. The load is the forearm itself and anything that may be held in the hand.
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The effect of third-class levers is the opposite of that of second-class levers. With third-class levers, speed and distance of load movement are increased, but at the expense of decreased strength. In other words, a large force is needed to move a relatively small load far and fast. In fact, the force required to move a load is increased the closer it is to the fulcrum. With forearm flexion, the load, or the weight in the hand, is six times further from the fulcrum than the applied force - that is, the biceps brachii attachment to the forearm. Therefore, the force must be six times as great as the load in order to move it. However, the load is moved far and fast.
Lesson Summary
In summary, body movement occurs when our muscles contract. Our muscles utilize three different lever systems to move our body. In the lever systems in the body, the fulcrum is the joint, the force is muscular contraction and the load is the weight of the body part moved. Head extension is an example of a first-class lever in which the load and force are on opposite sides of the fulcrum. Plantar flexion is a good example of a second-class lever in which the load is located between the applied force and fulcrum. Third-class levers are most common in the body; for example, forearm flexion, in which the applied force is between the load and the fulcrum. If you can remember FRE 123, you can remember what is in the middle of each lever. The fulcrum, beginning with 'F,' is in the middle of first-class levers, resistance, beginning with 'R,' is in the middle of second-class levers, and force, or effort, beginning with 'E,' is in the middle of third-class levers.
Learning Outcome
After viewing this lesson, students should be able to:
- Understand how our muscles work
- Define fulcrum, resistance and effort (FRE)
- Recall the three types of lever and how they work
To unlock this lesson you must be a Study.com Member.
Create your account
Frequently Asked Questions
What are 1st 2nd and 3rd class levers?
First-class levers occur when the pivot is located between the effort and load. Second-class levers occur when the load is between the effort and pivot. Third-class levers occur when the effort is between the load and the pivot.
What is an example of a first class lever in the human body?
An example of a first-class lever in the human body is the joint formed by the top of the vertebral column and skull, which is known as the atlanto-occipital joint. In this lever system, the muscles at the back of the neck provide the force needed to move the head backwards, which is a movement known as neck extension.
Is a human foot a first class lever?
The human foot is an example of a second-class lever. In this lever system, the toes are the pivot, the weight of the person is the load, and the calf muscles are the effort. The calf muscle provides the force needed to lift the body upward at the toes. This movement of the toes and ankle to stand on the tip toes is known as plantar flexion.
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BackMuscle Levers in the Body Systems & Examples | Which Parts of the Body Act As Levers?
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