Introduction to kinesiology (Biomechanics- Physiotherapy) vandana7381
Chapter 1: Introduction to Kinesiology ( Biomechanics) for physical therapy students.
Reference: JOINT STRUCTURE AND FUNCTION - by Pamela K. Levangie.
Easy to understand and with lot of examples.
Kinesiology of Moving objects : Push and Pull
Objectives:
Define push and pull patterns of motion.
Analyze mechanical factors that affecting to push-and-pull activities.
Identify the activities that involves push and pull patterns and give examples.
2. Aims
• Ground reaction
– What is it?
– What can we see in the gait graphs?
• Joint moments
– What are they?
– What can we see in the gait graphs?b
2
4. Forces (in general)
• If no forces act on an object it will continue
to move in a straight line at constant speed.
• This is often hidden because of:
– Friction
– Air resistance
5. Forces in different directions
• Any force will only cause a change of speed
in the direction in which it is acting so we
can think about forces acting in different
directions separately.
• We’ll look first at a simple case of how
forces act in a horizontal direction.
6. Forces (in general)
• If you want to change the speed at which
an object moves you have to apply a force.
No forces acting
Ball stays still (for ever)
7. Forces (in general)
• If you want to change the speed at which
an object moves you have to apply a force.
Apply a force
Ball moves in direction of
force
8. Forces (in general)
• If you want to change the speed at which
an object moves you have to apply a force.
Stop applying force
Ball continues to move at
same speed (for ever)
9. Forces (in general)
• If you want to change the speed at which
an object moves you have to apply a force.
Apply another force
Ball starts to move faster
(acceleration)
10. Forces (in general)
• If you want to change the speed at which
an object moves you have to apply a force.
Stop applying force
Ball continues to move at
same speed (for ever)
11. Forces (in general)
• If you want to change the speed at which
an object moves you have to apply a force.
No forces acting
Ball stays still (for ever)
12. Forces (in general)
• If you want to change the speed at which
an object moves you have to apply a force.
Apply a force
Ball moves in direction of
force
13. Forces (in general)
• If you want to change the speed at which
an object moves you have to apply a force.
Stop applying force
Ball continues to move at
same speed (for ever)
14. Forces (in general)
• If you want to change the speed at which
an object moves you have to apply a force.
Apply another force
Ball starts to move faster
(acceleration)
15. Forces (in general)
• If you want to change the speed at which
an object moves you have to apply a force.
Stop applying force
Ball continues to move at
same speed (for ever)
16. Forces
• When a force is applied the object changes
the speed of movement – it accelerates
• Speed of movement does not change
unless a force is acting.
17. Forces (in general)
• A force is also required if you want to slow
an object down
No forces acting
Ball moves at constant
speed
18. Forces (in general)
• A force is also required if you want to slow
an object down
Force against motion
Ball slows down
(deceleration)
19. Forces (in general)
• A force is also required if you want to slow
an object down
Remove force
Ball continues at slower
speed
20. Forces (in general)
• A force is also required if you want to slow
an object down
Force against motion
Ball stops
21. Acceleration and Deceleration
• If you apply a force in the direction that the
object is already moving its speed will
increase (acceleration)
• If you apply a force opposite to the direction
in which the object is already moving its
speed will decrease (deceleration)
• There is no difference between these forces
(apart from the direction in which they are
acting)
22. Acceleration and Deceleration
• The change of speed is proportional to the
force: the bigger the force the more the
speed changes.
• It is inversely proportional to the mass of
the object: the lighter the object the more
the speed will change (for the same force)
23. Take home
• Objects continue to move at constant speed
unless a force acts.
• The bigger the force the bigger the change
in speed.
24. Vertical forces and gravity
• Gravity acts on all objects.
• It always acts downwards.
• Unless another force is acting on an object
then the object will accelerate downwards
25. Vertical forces and gravity
Gravity always acts downwards
The ball doesn’t move
An equal force must be acting upwards
This force is called a “reaction”
26. Vertical forces and gravity
Remove support
No reaction
Ball will accelerate downwards
27. Vertical forces and gravity
Still no support
Still no reaction
Ball will accelerate downwards more
29. “Components of force”
• We can always split the force into
components: one horizontal and one
vertical
Vertical
component
Horizontal
component
30. “Components of force”
• We can treat the components as if they are
two different forces.
Vertical
component
Horizontal
component
will accelerate/decelerate
object vertically
will accelerate/decelerate
object horizontally
36. Ground reaction in walking
• Components of ground
reaction can be displayed
exactly as joint angles
• Both vertical (top) and
horizontal (bottom)
component grapsh have
characteristic shapes (like
joint angles)
Forwards
Backwards
Up
47. 47
Fore-aft component of ground reaction largely a
consequence of alignment of segments
(requires little more muscle activity than that required to
maintain that alignment)
49. Cyclic walking
49
Average vertical component
(on both feet) must be equal
to bodyweight
Average horizontal component
(on both feet) must be equal to
zero
61. Calculating moments
61
• Ounpuu, O., R. Davis, and P. Deluca, Joint kinetics: Methods, interpretation and treatment decision-
making in children with cerebral palsy and myelomeningocele. Gait and Posture, 1996. 4: p. 62-78.
