Types of Machines in the Body - Lever Systems

Question 1

What are the 4 main components of a lever system?

Answer 1

1) Lever arm (bones)
2) Fulcrum or axis of rotation (A)
3) Force of the muscle (F)
4) Resistance of body weight (R)

Question 2

What is the equation for ‘mechanical advantage’?

Answer 2

Mechanical advantage = Length of Force Arm / Length of Resistance Arm

Question 3

What is a 1st class lever? Example?

Answer 3

1st class lever is when the axis of rotation is in the middle, with resistance and force on either side.

Example: Nodding head on neck
Lever - Skull
Axis of Rotation - Atlanto-occipital joint
Resistance - Weight of skull
Force - Contraction of posterior neck muscles

Question 4

What is a 2nd class lever? Example?

Answer 4

2nd class lever is when the resistance and muscle force are applied on the same side from the axis of rotation, but muscle force is further away (has a longer lever)

Example: Plantar flexion
Lever - Interlocked bones of foot
Axis of rotation - 1st metatarsophalangeal joint (ball of big toe)
Resistance - Weight of body (centre of mass behind pivot)
Force - Contraction of posterior calf muscles

Question 5

What is a 3rd class lever? Example?

Answer 5

3rd class lever is when resistance and muscle force are applied on the same side from the axis of rotation, but muscle force is closer.

Example: Elbow flexion
Lever - Bones of forearm
Axis of rotation - Elbow joint
Resistance - Weight of forearm and hand
Force - Contraction of Biceps Brachii

Question 6

What are 3rd class levers ‘designed’ for?

Answer 6

Speed and range of movement