The mechanics in biomechanics

Сентябрь 15, 2022

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The mechanics in biomechanics

Содержание

2. Outline Mechanics and its application to biological systems Forms of motion Levers Balance and center of
3. How Did It Walk? Mallison, H. (2010). CAD assessment of the posture and range of motion
4. How Did It Walk? https://www.youtube.com/watch?v=dJNjm_k25zE
5. Mechanics and Biomechanics Mechanics: science that deals with physical energy and forces and their effect on
6. Performance
7. Medicine
8. Recovery
9. Forms of Motion Linear motion: motion along a line Rectilinear motion: (along a straight line) Curvilinear
10. Forms of Motion
11. Levers Humans move using a system of levers lever is a rigid bar that turns about
12. Levers Levers rotate when a force (effort, E) is being applied against a resistance or weight
13. Why Use Levers? Levers perform two main functions: To increase the resistance (or load) that can
14. Levers Three possible orientations of the fulcrum, force and resistance determine the types of lever Axis
15. The First Class of Levers First class Levers In a first class lever the fulcrum is
16. First Class Lever O
17. The Second Class of Levers Second class levers Here the resistance is between the fulcrum and
18. Second Class Lever FE FR O
19. The Third Class of Levers Third class Levers Here the effort is between the fulcrum and
20. Third Class Lever O
21. Human Body Levers Human’s levers are mostly built for speed and range of movement at expense
22. Example 1. How much force (in kg) needs to be applied to move 45 kg when
23. Example FE x 0.05 meters = 45 kg x 0.25 meters FE x 0.05 = 11.25
24. Lever Length Where is the velocity or speed the greatest; at A’ or B’? How can
25. Lever Length A longer lever increases the speed at the end of the racquet unless the
26. Stability Center of gravity (CG): Point at which all parts of a body are equally balanced
27. Center of Gravity The center of gravity can be shifted by stretching, bending, changing position The
28. Base of support The BOS area can be changed Larger BOS area is typical for more
29. Line of Gravity The line of gravity is always vertical The LOG must outside the base
30. Stability Someone is more __________when they have a _______centre of _______, a ______ base of __________
31. Disadvantages Loss of speed Loss of agility Loss of stability Advantages Carry food Carry tools Increased
32. Interesting Fact: T Rex Arms How much could T Rex lift with its arm? (50x6=300lbs ≈136kg)
33. Open Question Do artificial legs provide an unfair advantage? If yes, how? If no, why?
34. Summary Mechanics and its application to biological systems Scope of biomechanics Types of motion Levers in
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Outline
Mechanics and its application to biological systems
Forms of motion
Levers
Balance and center

of gravity

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How Did It Walk?
Mallison, H. (2010). CAD assessment of the posture

and range of motion of Kentrosaurus aethiopicus Henning 1915 Swiss Journal of Geosciences, 103, 211-233
http://scienceblogs.com/tetrapodzoology/2011/01/05/heinrichs-digital-kentrosaurus/

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How Did It Walk?
https://www.youtube.com/watch?v=dJNjm_k25zE

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Mechanics and Biomechanics
Mechanics: science that deals with physical energy and forces

and their effect on objects
Biomechanics - study of the mechanics as it relates to the functional and anatomical analysis of biological systems and especially humans

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Performance

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Medicine

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Recovery

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Forms of Motion
Linear motion: motion along a line
Rectilinear motion: (along

a straight line)
Curvilinear motion: (along a curved line)

Angular motion: rotation around an axis

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Forms of Motion

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Levers
Humans move using a system of levers
lever is a rigid bar

that turns about an axis of rotation or a fulcrum
axis is the point of rotation about which lever moves
levers can be utilized more or less efficiently

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Levers
Levers rotate when a force (effort, E) is being applied against

a resistance or weight
In the body
bones are the bars
joints are the axes
muscles contract to apply force
weights or external loads are the resistance

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Why Use Levers?
Levers perform two main functions:
To increase the resistance

(or load) that can be moved with
a given effort e.g. a crowbar.
To increase the velocity at
which an object will move with a
given force. e.g. a golf club.

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Levers
Three possible orientations of the fulcrum, force and resistance determine the

types of lever
Axis (O)- fulcrum - the point of rotation
Applied force FE (usually muscle contraction)
Resistance force FR (can be weight or/and external loads)

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The First Class of Levers
First class Levers
In a first class lever

the fulcrum is between the effort and the resistance.
This type of lever can increase the effects of the effort and the speed of a body. Also good for keeping balance.

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First Class Lever
O

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The Second Class of Levers
Second class levers
Here the resistance is between

the fulcrum and the effort.
This type of lever is generally thought to increase only the effect of the effort force.

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Second Class Lever
FE
FR
O

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The Third Class of Levers
Third class Levers
Here the effort is between

the fulcrum and the resistance and can be seen in the.
They can increase the body’s ability to move quickly but in terms of applying force they are very inefficient.

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Third Class Lever
O

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Human Body Levers
Human’s levers are mostly built for speed and range

of movement at expense of force
Thus, short force arms and long resistance arms require great muscular strength for movement
Examples: biceps and triceps attachments
biceps force arm is 1 to 2 inches (1inch=2.54cm)
triceps force arm is less than 1 inch

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Example
1. How much force (in kg) needs to be applied to

move 45 kg when the RA is 0.25 m and the EA is 0.05 meters?
Use the formula
FE x EA = FR x RA
Note: kgs are not units of force, but sometimes force is divided by g(9.8m/s2) and expressed in kilograms.

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Example
FE x 0.05 meters = 45 kg x 0.25 meters
FE x

0.05 = 11.25 kg
FE = 225 Kg
45

EA = 0.05

RA = 0.25

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Lever Length
Where is the velocity or speed the greatest; at A’

or B’?
How can this principle be applied to tennis?

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Lever Length
A longer lever increases the speed at the end of

the racquet unless the extra weight is too great. Then the speed may actually be slower.

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Stability
Center of gravity (CG): Point at which all parts of

a body are equally balanced
Base of support (BOS): Area within an object’s point of contact with the ground
Line of gravity (LOG): Direct line from the center of gravity to the ground

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Center of Gravity
The center of gravity can be shifted by stretching,

bending, changing position
The center of gravity can be outside of the body
Low center of gravity is typical for more stable positions

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Base of support
The BOS area can be changed
Larger BOS area is

typical for more stable positions
In humans, wide BOS is usually accompanied by low CG

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Line of Gravity
The line of gravity is always vertical
The LOG must

outside the base of support to initiate or continue movement
The further away the LOG from the BOS, the greater the tendency to move in that direction

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