1. Simple body
machines

2. Simple body machines It include: 1- Levers. 2- Pullys.
3- Wheel and axle.

3. Why study a Simple Machine?
Simple Machines make work easier by giving the user a mechanical advantage.
There are many examples of simple machines inside the body.
Simple machines must be well known to determine the level of performance of athletic player.
As a result, it will help the biomechanists to improve the players’ performance

4. Lever System Definition
Force
Lever is a simple machine, which consists of a rigid bar that can move or rotate around a fixed point or fulcrum when a force is applied to overcome resistance.
Resistance
Rigid bar
Fulcrum

5. Human equivalents 1- Bone › Rigid bar 2- Joint axis › Fulcrum
3- Muscles › Effort.
4- Resistance › Weight
5- Effort arm › Moment arm
of the muscle force
6- Resistance arm › Moment arm of LOG

6. Effort Arm Resistance Arm
Mechanical Advantage (MA)
Definition
It is the way to measure the efficiency of this machine that means the ability of the machine to magnify force or to increase the output in relation to the input.
Mechanical advantage of the lever =
Effort Arm Resistance Arm

7. Effort arm ˃ Resistance arm Effort arm ˂ Resistance arm
If MA= 1
Effort arm = Resistance arm
The Function:
1. change the direction
2. Balance
If MA ˃ 1
Effort arm ˃ Resistance arm
The Function:
1. Magnify force
If MA ˂ 1
Effort arm ˂ Resistance arm
The Function:
1. Magnify speed
2. Range of motion

8. Classification of Lever
1.First class of lever
2. Second class of lever
3. Third class of lever

9. 1 . First class of lever
It is a class of lever at which the fulcrum is located between the point at which the force is applid and the resistance.
Crowbar
Scissors
See-saw
Effort
Fulcrum
Load

10. MA may be
One
Greater than one
Less than one R R E E R E F F F

11. Functions of first class of lever
Change direction of force
Balance of force
Magnify force
Speed and ROM

12. At the insertion of the muscle
Anatomical examples
In axial skeleton:
The action of the muscles of the neck against the weight of the head in the upright position
The fulcrum
Atlanto occipital joint
The effort
Neck extensor muscles
The resistance
The weight of the head
At the insertion of the muscle
POA of Effort
POA of
Resistance
At the segmental COG of the head

13. In upper limb:
The action of the triceps brachii muscle in extending the forearm.
The fulcrum
Elbow joint
The effort
Triceps muscle
The resistance
The weight of the forearm and hand
POA of Effort
At the insertion of triceps muscle
POA of
Resistance
At the segmental COG of the forearm and hand

14. At the insertion of muscle
In lower limb:
The action of the planter flexors muscle during ankle planter flexion in non-weight bearing
The fulcrum
Ankle joint
The effort
Plantar flexor muscles
The resistance
The weight of the foot
POA of Effort
At the insertion of muscle
POA of
Resistance
At the segmental COG of the foot

15. Within the human body the action of agonists and antagonist muscle groups is considered first class of lever

16. 2 . Second class of lever
It is a class of lever at which the resistance is located between the fulcrum and the effort.
Wheel Barrow
Nut cracker

17. The effort arm is always bigger than the resistance arm.
EA ˃ RA
MA ˃ 1

18. Functions of second class of lever
Magnify force
Conserve energy

19. Anatomical examples In axial skeleton:
The action of masseter muscle during eating.
The fulcrum
Temporomandibular joint
The effort
Masseter muscle
The food when it is located at the posterior aspect of the mouth
The resistance
POA of Effort
At the insertion of masseter muscle
POA of
Resistance
The COG of the food

20. In upper limb:
The action of the brachioradialis muscle during elbow flexion.
The fulcrum
Elbow joint
The effort
brachioradialis muscle
The resistance
The weight of the forearm and hand
POA of Effort
At the insertion of brachioradialis muscle
POA of
Resistance
At the segmental COG of the forearm and hand

21. In lower limb:
The action of the calf muscle in weight bearing plantar flexion which is called calf raise.
The fulcrum
The base of the toes.
The effort
Ankle plantar flexors.
The resistance
The weight of the body.
At the insertion of planter flexors muscle.
POA of Effort
At the total body COG represented by LOG anterior to ankle joint.
POA of
Resistance

22. 3 . Third class of lever
It is a class of lever at which the effort is located between the fulcrum and the resistance.
Shovel
Fishing rod

23. The resistance arm is always bigger than the effort arm.
EA ˂ RA
MA ˂ 1

24. Functions of third class of lever
Increase ROM
Increase speed

25. Temporomandibular joint At the insertion of masseter muscle
Anatomical examples
In axial skeleton:
The action of masseter muscle when a bite force is applied in the front of mouth
The fulcrum
Temporomandibular joint
The effort
Masseter muscle
The food when a bite force is applied in the front of mouth.
The resistance
At the insertion of masseter muscle
POA of Effort
POA of
Resistance
The food

26. In upper limb: The action of the biceps muscle during elbow flexion.
The fulcrum
Elbow joint
The effort
biceps muscle
The resistance
The weight of the forearm and hand
POA of Effort
At the insertion of biceps muscle
POA of
Resistance
At the segmental COG of the forearm and hand

27. In lower limb:
The action of the quadriceps muscle during knee extension.
The fulcrum
The knee joint.
The effort
quadriceps muscle.
The resistance
The weight of the leg and foot.
POA of Effort
At the insertion of the quadriceps muscle.
At the segmental COG of the leg and foot.
POA of
Resistance

28. The class of lever involved in most of sports activities is third one, as these activities require great speed and RON. For example : in tennis players and football players.

29. For example:
Throwing a ball involves levers at shoulder, elbow, & wrist joints
The longer the lever, the more effective it is in imparting velocity
A tennis player can hit a tennis ball harder with a straight-arm drive than with a bent elbow because the lever (including the racket) is longer & moves at a faster speed

30. Class of lever in two-joint muscle
Definition:
Two-joint muscles are muscles, which pass over two joints at the same time. They are also called biarticular muscle.
For example
Rectus femoris:
Second class over the proximal joint (hip joint)
Third class over the distal joint (knee joint)

31. Remember
A mechanical advantage less than one doesn’t mean a machine isn’t useful. It just means that instead of multiplying force, the machine multiplies distance.
A broom doesn’t push the dust with as much force as you use to push the broom, but a small movement of your arm pushes the dust a large distance.

32. Solve
Sometimes levers are used to multiply distance. For a broom, your upper hand is the fulcrum and your lower hand provides the input force.
The mechanical advantage of this
broom is:
The answer:
MA = 0.3 / 1.2
MA = 0.25

33. Pulley is a simple machine, that performs a mechanical job.
Definition
Pulley is a simple machine, that performs a mechanical job.
It consists of a grooved wheel and a cord or a rope running over it

34. Types of pulleys
1. Fixed pulley
2. Mobile pulley
3. Mixed pulley

35. Fixed pulley It is the only example of pulley in human body
A fixed pulley changes the direction of a force.
Mechanical advantage = 1

36. mobile pulley It is used in exercises.
The mechanical advantage of a mobile pulley is equal to the number of ropes that support the mobile pulley.

37. Mixed pulley It is used in exercises.
The combination between fixed and mobile pulleys.
Mixed pulleys acts to increase mechanical advantage.
Each additional rope increases mechanical advantage by 1.

38. Functions of pulleys Change direction of force Balance of force
Modify the effect of a force
Magnify the force via increasing the MA

39. 1. Wheel: Represented by bony component which can be
Human equivalents
1. Wheel: Represented by bony component which can be
External bone: as patella
Bony prominence: as condyles, trochanters, tuberosities
2. Rope or Cord: is represented by tendon, muscle, musculotendinous junction.

40. Patella as a pulley
Patella acts as an external pulley for the tendon of quadriceps muscle tendon

41. Patella has the following functions
Move the muscle away
Increase the moment arm
Increase the quadriceps torque
Increase the angle of pull
Increase the rotatory component
Increase the efficiency of quadriceps muscle
Improve the mechanical advantage

42. Lateral malleolus bone as a pulley
lateral malleolus acts as a pulley around which tendon of peroneus longus runs.
As peroneus longus contracts, it pulls toward it belly (toward the knee).
Using the lateral malleolus as a pulley, force is transmitted to plantar aspect of foot resulting in eversion/plantarflexion.
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