0
Upcoming SlideShare
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Standard text messaging rates apply

# Why we walk (2014 kinetics)

531

Published on

2 Likes
Statistics
Notes
• Full Name
Comment goes here.

Are you sure you want to Yes No
Your message goes here
• Be the first to comment

Views
Total Views
531
On Slideshare
0
From Embeds
0
Number of Embeds
4
Actions
Shares
0
0
0
Likes
2
Embeds 0
No embeds

No notes for slide

### Transcript

• 1. Kinetics Richard Baker Professor of Clinical Gait Analysis Blog: wwRichard.net 1
• 2. Aims &#x2022; Ground reaction &#x2013; What is it? &#x2013; What can we see in the gait graphs? &#x2022; Joint moments &#x2013; What are they? &#x2013; What can we see in the gait graphs?b 2
• 3. Ground Reaction Force What is it? 3
• 4. Forces (in general) &#x2022; If no forces act on an object it will continue to move in a straight line at constant speed. &#x2022; This is often hidden because of: &#x2013; Friction &#x2013; Air resistance
• 5. Forces in different directions &#x2022; 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. &#x2022; We&#x2019;ll look first at a simple case of how forces act in a horizontal direction.
• 6. Forces (in general) &#x2022; 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) &#x2022; 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) &#x2022; 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) &#x2022; 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) &#x2022; 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) &#x2022; 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) &#x2022; 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) &#x2022; 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) &#x2022; 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) &#x2022; 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 &#x2022; When a force is applied the object changes the speed of movement &#x2013; it accelerates &#x2022; Speed of movement does not change unless a force is acting.
• 17. Forces (in general) &#x2022; 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) &#x2022; A force is also required if you want to slow an object down Force against motion Ball slows down (deceleration)
• 19. Forces (in general) &#x2022; A force is also required if you want to slow an object down Remove force Ball continues at slower speed
• 20. Forces (in general) &#x2022; A force is also required if you want to slow an object down Force against motion Ball stops
• 21. Acceleration and Deceleration &#x2022; If you apply a force in the direction that the object is already moving its speed will increase (acceleration) &#x2022; If you apply a force opposite to the direction in which the object is already moving its speed will decrease (deceleration) &#x2022; There is no difference between these forces (apart from the direction in which they are acting)
• 22. Acceleration and Deceleration &#x2022; The change of speed is proportional to the force: the bigger the force the more the speed changes. &#x2022; 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 &#x2022; Objects continue to move at constant speed unless a force acts. &#x2022; The bigger the force the bigger the change in speed.
• 24. Vertical forces and gravity &#x2022; Gravity acts on all objects. &#x2022; It always acts downwards. &#x2022; 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&#x2019;t move An equal force must be acting upwards This force is called a &#x201C;reaction&#x201D;
• 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
• 28. &#x201C;Components of force&#x201D; &#x2022; Forces very rarely act purely horizontally or vertically.
• 29. &#x201C;Components of force&#x201D; &#x2022; We can always split the force into components: one horizontal and one vertical Vertical component Horizontal component
• 30. &#x201C;Components of force&#x201D; &#x2022; 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
• 31. Ground reaction in walking Measured with force plate
• 32. Ground reaction in walking Vertical component Horizontal component
• 33. Ground reaction in walking &#x2022; Vertical component can only act upwards &#x2022; Horizontal force can act backwards (here)
• 34. Ground reaction in walking &#x2022; Vertical component can only act upwards &#x2022; Horizontal force can act backwards (here) &#x2022; Or forwards (here)
• 35. Ground Reaction What can we see in the gait graphs? 35
• 36. Ground reaction in walking &#x2022; Components of ground reaction can be displayed exactly as joint angles &#x2022; Both vertical (top) and horizontal (bottom) component grapsh have characteristic shapes (like joint angles) Forwards Backwards Up
• 37. Vertical component 37
• 38. Trajectory of centre of mass 38
• 39. Upward acceleration 39 A B BA Warning: This is not what you read in many text books!
• 40. 40 A B C BA C Upward deceleration
• 41. Downward acceleration 41 A B C D BA C D
• 42. Downward deceleration 42 A B C D E BA C D E Warning: This is not what you read in many text books!
• 43. Horizontal component 43
• 44. Trajectory of centre of mass 44
• 45. Forwards acceleration 45 BA C A B C
• 46. Forwards acceleration 46 BA C D E A B C D E
• 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)
• 48. Cyclic walking 48
• 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
• 50. Joint moments What are they? 50
• 51. Moment &#x2013; Angular &#x201C;force&#x201D; 51
• 52. Moment arising from force 52
• 53. Moment arising from force 53 Moment is proportional to size of force
• 54. Moment arising from force 54 Moment is proportional to perpendicular distance from pivot
• 55. Moment arising from force 55 Moment independent of direction of force
• 56. Moment arising from force 56 Force acting in opposite sense will give opposite moment
• 57. 57 Forwards Know forces and moments What are accelerations? Know forces and accelerations What are moments? Inverse
• 58. 58 Moment tells us which muscle group is dominant Only tell us which group is dominant Tell us nothing about antagonistic activity
• 59. Calculating moments 59
• 60. Calculating moments 60
• 61. Calculating moments 61 &#x2022; 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.
• 62. Ankle moment 62 AM1
• 63. Ankle moment 63 AM2
• 64. Ankle moment 64 AM3
• 65. Ankle moment 65 AM2AM1 AM3
• 66. Knee moment 66 KM1
• 67. Knee moment 67 KM2
• 68. Knee moment 68 KM3
• 69. Knee moment 69 KM4
• 70. Knee moment KM5
• 71. Knee moment 71 KM6
• 72. Knee moment 72 KM6KM5KM4KM3KM2KM1
• 73. Hip moment 73 HM4
• 74. Hip moment 74 HM4
• 75. Hip moment 75 HM4
• 76. Hip moment 76 HM4
• 77. Hip moment 77 HM2 HM5HM4HM1 HM2
• 78. Hip moment 78 HM2 HM5HM4HM1 HM2
• 79. 79
• 80. 80
• 81. Thanks for listening Richard Baker Professor of Clinical Gait Analysis Blog: wwRichard.net 81