Q: A person is sitting on a seesaw with their body weight (BW) of 67.2 N at a distance of 0.91 m from the pivot. If the seesaw is balanced, what is the torque produced by the body weight?

$$67.2 \times 0.91 = 61.3\ \mathrm{Nm}$$

Q: Given the torque equation $$MF \times IMA = EF \times EMA$$, if $$IMA = 0.02\ \mathrm{m}$$, $$EMA = 0.10\ \mathrm{m}$$, and $$EF = 50\ \mathrm{N}$$, what muscle force $$MF is $$required to balance the system?

$$MF = \frac{EF \times EMA}{IMA} = \frac{50 \times 0.10}{0.02} = 250\ \mathrm{N}$$

Question 1

Which of the following best describes a first-class lever in the human body?

Accepted Answer

The axis of rotation is positioned between the internal and external forces.

Question 2

A person is sitting on a seesaw with their body weight (BW) of 67.2 N at a distance of 0.91 m from the pivot. If the seesaw is balanced, what is the torque produced by the body weight?

Accepted Answer

$$67.2 	imes 0.91 = 61.3\ \mathrm{Nm}$$

Question 3

Which of the following statements about second-class levers in the musculoskeletal system is correct?

Accepted Answer

The external force is located between the axis of rotation and the internal force.

Question 4

In a third-class lever, such as the elbow flexor system, which of the following is true regarding the mechanical advantage (MA)?

Accepted Answer

MA is always less than 1.

Question 5

If a muscle produces a force of 100 N with an internal moment arm (IMA) of 0.03 m, and the external force has an external moment arm (EMA) of 0.09 m, what is the mechanical advantage (MA) of the muscle-joint system?

Accepted Answer

$$MA = \frac{IMA}{EMA} = \frac{0.03}{0.09} = 0.33$$

Question 6

A person stands on tiptoe, using the ball of the foot as a pivot. Which class of lever is this, and what is the mechanical advantage?

Accepted Answer

Second-class lever; MA greater than 1

Question 7

Which of the following best explains why most muscles in the human body must produce a force much greater than the external load they move?

Accepted Answer

Most musculoskeletal levers have a mechanical advantage much less than 1.

Question 8

Given the torque equation $$MF 	imes IMA = EF 	imes EMA$$, if $$IMA = 0.02\ \mathrm{m}$$, $$EMA = 0.10\ \mathrm{m}$$, and $$EF = 50\ \mathrm{N}$$, what muscle force $$MF is $$required to balance the system?

Accepted Answer

$$MF = \frac{EF 	imes EMA}{IMA} = \frac{50 	imes 0.10}{0.02} = 250\ \mathrm{N}$$

Question 9

Which of the following is a real-world example of a first-class lever in the human body?

Accepted Answer

The head-and-neck extensors balancing the head over the vertebral column

Question 10

A patient with a paralyzed triceps muscle cannot extend their elbow. Which lever class is primarily affected, and what is the likely functional consequence?

Accepted Answer

Third-class lever; inability to produce rapid extension of the forearm

Question 11

If the mechanical advantage (MA) of a lever is less than 1, which of the following must be true?

Accepted Answer

The internal moment arm is shorter than the external moment arm.

Question 12

Which of the following best describes the trade-off between force and distance in musculoskeletal levers?

Accepted Answer

A small mechanical advantage allows for greater speed and range of motion at the expense of force.

Question 13

A muscle produces a force of 200 N with an internal moment arm of 0.02 m. If the external moment arm is 0.10 m, what is the maximum external force that can be balanced?

Accepted Answer

$$EF = \frac{MF 	imes IMA}{EMA} = \frac{200 	imes 0.02}{0.10} = 40\ \mathrm{N}$$

Question 14

Which of the following is NOT a characteristic of third-class levers in the human body?

Accepted Answer

They always have a mechanical advantage greater than 1.

Question 15

A surgeon increases the length of the internal moment arm for the elbow flexor muscles. What is the likely effect on the mechanical advantage and muscle force required?

Accepted Answer

Mechanical advantage increases; muscle force required decreases

Question 16

Which equation correctly expresses the balance of torques for a musculoskeletal lever?

Accepted Answer

$$MF 	imes IMA = EF 	imes EMA$$

Question 17

Why do most musculoskeletal levers have a mechanical advantage less than 1?

Accepted Answer

To allow greater speed and range of motion at the joint

Question 18

Which of the following best describes the effect of increasing the external moment arm (EMA) while keeping the internal moment arm (IMA) constant?

Accepted Answer

The mechanical advantage decreases, requiring greater muscle force to balance the same external force.

Question 19

A person is holding a weight in their hand with the elbow flexed at 90 degrees. The biceps brachii is acting as which class of lever, and what is the typical mechanical advantage?

Accepted Answer

Third-class lever; MA less than 1

Levers in the Musculoskeletal System: Types, Mechanics, and Applications

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