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Questions and Answers
In a third-class lever system, such as the human elbow joint during a bicep curl, what is the relationship between the muscle force ($F_M$), the resistive force ($F_R$), and their respective moment arms ($M_M$ and $M_R$)?
In a third-class lever system, such as the human elbow joint during a bicep curl, what is the relationship between the muscle force ($F_M$), the resistive force ($F_R$), and their respective moment arms ($M_M$ and $M_R$)?
- $F_M$ is equal to $F_R$, and $M_M$ is equal to $M_R$.
- $F_M$ is greater than $F_R$, and $M_M$ is less than $M_R$. (correct)
- $F_M$ is less than $F_R$, and $M_M$ is greater than $M_R$.
- $F_M$ is less than $F_R$, and $M_M$ is less than $M_R$.
Why do skeletal muscles typically operate at a mechanical disadvantage?
Why do skeletal muscles typically operate at a mechanical disadvantage?
- To allow for greater precision in movements requiring high force output.
- To minimize the stress on tendons and ligaments.
- To reduce the amount of energy required for muscle contraction.
- To maximize the range of motion and speed of movement, even at the expense of force. (correct)
During elbow flexion, how does the changing perpendicular distance from the joint axis to the biceps tendon's line of action affect the mechanical advantage?
During elbow flexion, how does the changing perpendicular distance from the joint axis to the biceps tendon's line of action affect the mechanical advantage?
- As the distance increases, the mechanical advantage decreases.
- As the distance decreases, the mechanical advantage increases.
- The distance does not affect the mechanical advantage.
- As the distance increases, the mechanical advantage increases. (correct)
In a biceps curl exercise, the biceps muscle acts as the muscle force ($F_M$) and the weight in the hand acts as the resistive force ($F_R$). If the moment arm of the muscle ($M_M$) is significantly smaller than the moment arm of the resistance ($M_R$), what does this imply about the force the biceps must generate?
In a biceps curl exercise, the biceps muscle acts as the muscle force ($F_M$) and the weight in the hand acts as the resistive force ($F_R$). If the moment arm of the muscle ($M_M$) is significantly smaller than the moment arm of the resistance ($M_R$), what does this imply about the force the biceps must generate?
Which of the following statements is true regarding the relationship between muscle force, resistive force, and mechanical advantage in the human body?
Which of the following statements is true regarding the relationship between muscle force, resistive force, and mechanical advantage in the human body?
In a first-class lever system, how are the muscle force and resistive force arranged relative to the fulcrum?
In a first-class lever system, how are the muscle force and resistive force arranged relative to the fulcrum?
In a scenario where the moment arm of the muscle force (MM) is much smaller than the moment arm of the resistive force (MR) in a first-class lever system, what is the relationship between the muscle force (FM) and the resistive force (FR)?
In a scenario where the moment arm of the muscle force (MM) is much smaller than the moment arm of the resistive force (MR) in a first-class lever system, what is the relationship between the muscle force (FM) and the resistive force (FR)?
What is a key characteristic of a second-class lever?
What is a key characteristic of a second-class lever?
What is the relationship between muscle force (FM) and resistive force (FR) in a second-class lever system due to its mechanical advantage?
What is the relationship between muscle force (FM) and resistive force (FR) in a second-class lever system due to its mechanical advantage?
Which of the following best describes the relationship between the axial and appendicular skeleton?
Which of the following best describes the relationship between the axial and appendicular skeleton?
During a standing heel raise exercise, what serves as the fulcrum (O) in the context of lever mechanics?
During a standing heel raise exercise, what serves as the fulcrum (O) in the context of lever mechanics?
In the context of plantar flexion during a heel raise, if the moment arm of the muscle force (MM) is greater than the moment arm of the resistive force (MR), what is the relationship between the muscle force (FM) and the resistive force (FR)?
In the context of plantar flexion during a heel raise, if the moment arm of the muscle force (MM) is greater than the moment arm of the resistive force (MR), what is the relationship between the muscle force (FM) and the resistive force (FR)?
In the context of skeletal muscle function, what distinguishes the origin of a muscle from its insertion?
In the context of skeletal muscle function, what distinguishes the origin of a muscle from its insertion?
During a bicep curl, the bicep muscle is the prime mover. What role does the triceps muscle play in this movement?
During a bicep curl, the bicep muscle is the prime mover. What role does the triceps muscle play in this movement?
A lever system has a mechanical advantage of 0.125. What does this indicate about the muscle force required compared to the resistive force?
A lever system has a mechanical advantage of 0.125. What does this indicate about the muscle force required compared to the resistive force?
Which of the following scenarios best illustrates a second-class lever system in the human body?
Which of the following scenarios best illustrates a second-class lever system in the human body?
A lever system has a mechanical advantage greater than 1.0. How does this influence the force required from the muscle?
A lever system has a mechanical advantage greater than 1.0. How does this influence the force required from the muscle?
In a first-class lever system within the musculoskeletal system, which of the following arrangements is correct?
In a first-class lever system within the musculoskeletal system, which of the following arrangements is correct?
During a triceps extension exercise, if the moment arm of the muscle force (MM) is shorter than the moment arm of the resistive force (MR), what does this indicate?
During a triceps extension exercise, if the moment arm of the muscle force (MM) is shorter than the moment arm of the resistive force (MR), what does this indicate?
A weightlifter is performing a deadlift. At a certain point in the lift, the force applied to the bar is equal in magnitude but opposite in direction to the force resisting the bar's movement (FR). What does this indicate about the lever system at that instant?
A weightlifter is performing a deadlift. At a certain point in the lift, the force applied to the bar is equal in magnitude but opposite in direction to the force resisting the bar's movement (FR). What does this indicate about the lever system at that instant?
If a person is lifting a heavy object, and the moment arm of the resistive force (MRF) is significantly longer than the moment arm of the applied force (MAF), what strategy could they employ to reduce the required muscle force?
If a person is lifting a heavy object, and the moment arm of the resistive force (MRF) is significantly longer than the moment arm of the applied force (MAF), what strategy could they employ to reduce the required muscle force?
Flashcards
Third-Class Lever
Third-Class Lever
Muscle force and resistive force act on same side of fulcrum; muscle force acts through shorter moment arm than resistive force.
Moment Arm (M)
Moment Arm (M)
The perpendicular distance from the joint axis of rotation to the tendon's line of action.
Mechanical Advantage
Mechanical Advantage
Ratio of muscle force moment arm to resistive force moment arm. >1.0 means less effort.
Muscle Mechanical Disadvantage
Muscle Mechanical Disadvantage
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Muscle Force
Muscle Force
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Muscles & Skeleton
Muscles & Skeleton
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Axial vs. Appendicular Skeleton
Axial vs. Appendicular Skeleton
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Origin
Origin
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Insertion
Insertion
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Agonist Muscle
Agonist Muscle
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Antagonist Muscle
Antagonist Muscle
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First-Class Lever
First-Class Lever
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Second-Class Lever
Second-Class Lever
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Second-Class Lever Force
Second-Class Lever Force
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Figure 2.3
Figure 2.3
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Muscle Force (FM)
Muscle Force (FM)
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Resistive Force (FR)
Resistive Force (FR)
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Moment Arm of Muscle Force (MM)
Moment Arm of Muscle Force (MM)
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Study Notes
- Muscles function by pulling against bones to create movement.
- Muscles rotate bones about joints, transmitting force to the environment through the skin.
Skeletal Musculature
- A system of muscles enables the skeleton to move.
- The origin refers to the proximal attachment of a muscle.
- The insertion refers to the distal attachment of a muscle.
Agonist vs Antagonist
- The agonist is the muscle most directly involved in bringing about movement, also known as the prime mover.
- The antagonist is a muscle that can slow down or stop movement.
Levers of the Musculoskeletal System
- Many muscles in the body act through levers.
- Body movements in sport and exercise primarily act through bony levers of the skeleton.
- A lever is a rigid or semi-rigid body that exerts force on an object impeding its tendency to rotate when subjected to a force whose line of action doesn't pass through its pivot point.
The Lever
- A lever can transmit force tangential to the arc of rotation.
- FA = force applied to the lever
- MAF = moment arm of the applied force
- FR = force resisting the lever's rotation
- MRF = moment arm of the resistive force
- The lever applies a force on the object equal in magnitude but opposite in direction from FR
Mechanical Advantage
- Mechanical advantage is the ratio of the moment arm through which applied force acts to that through which a resistive force acts.
- A mechanical advantage greater than 1.0 allows the applied force to be less than the resistive force to produce an equal amount of torque.
- A mechanical advantage of less than 1.0 is a disadvantage.
First-Class Levers
- A first-class lever is one where the muscle force and resistive force act on opposite sides of a fulcrum.
A First-Class Lever (Elbow extension)
- Elbow extension against resistance is an example of a first-class lever arrangement.
- O = fulcrum
- FM = muscle force
- FR = resistive force
- MM = moment arm of the muscle force
- MR = moment arm of the resistive force
- For elbow extension: mechanical advantage = MM/MR = 5 cm/40 cm = 0.125. This value is less than 1.0 which is a disadvantage.
- With a first class lever the muscle force and resistive force act on opposite sides of the fulcrum.
- Because MM is much smaller than MR, FM must be much greater than FR, which shows the disadvantageous nature of the first-class lever arrangement.
Second-Class Levers
- A second-class lever has the muscle force and resistive force acting on the same side of the fulcrum.
- In a second-class lever the muscle force acts through a moment arm longer than that through which the resistive force acts.
- Second-class levers have a mechanical advantage, the required muscle force is less than the resistive force.
A Second-Class Lever (Plantar Flexion)
- Plantar flexion against resistance is an example of a second-class lever.
- FM = muscle force
- FR = resistive force
- MM = moment arm of the muscle force
- MR = moment arm of the resistive force
- When the body is raised during plantar flexion, the ball of the foot is the fulcrum.
- Because MM is greater than MR, FM is less than FR in plantar flexion.
Third-Class Levers
- A third-class lever is one where the muscle force and resistive force act on the same side of the fulcrum.
- The muscle force acts through a moment arm shorter than that through which the resistive force acts.
- The mechanical advantage is less than 1.0, so the muscle force has to be greater than the resistive force to produce torque equal to that produced by the resistive force.
A Third-Class Lever (Elbow Flexion)
- Elbow flexion against resistance is an example of a third-class lever.
- FM = muscle force
- FR = resistive force
- MM = moment arm of the muscle force
- MR = moment arm of the resistive force
- Because MM is much smaller than MR, FM must be much greater than FR.
Moment Arm and Mechanical Advantage
- During elbow flexion with the biceps muscle, the distance from the joint axis of rotation to the tendon's line of action varies.
- When the moment arm (M) is shorter, there is less mechanical advantage.
Key Point About Levers
- Most skeletal muscles operate at a considerable disadvantage.
- Forces in the skeletal muscles and tendons are much higher than those exerted by the hands or feet on external objects.
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Description
Explore how muscles function by pulling against bones to create movement and rotate bones about joints. Learn about the skeletal musculature system, including the roles of agonist and antagonist muscles. Discover how levers in the musculoskeletal system facilitate body movements.
