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Biomechanics

Biomechanics. Movement studies 2011. Adapted from 2010 slides produced by PR. Learning Outcomes. Define CoG, LoG, BoS and equilibrium and explain how they interrelate Briefly discuss the implications of CoG, LoG and BoS to human postures and movement

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Biomechanics

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  1. Biomechanics Movement studies 2011 Adapted from 2010 slides produced by PR University of Hertfordshire - MS 2011/12

  2. Learning Outcomes • Define CoG, LoG, BoS and equilibrium and explain how they interrelate • Briefly discuss the implications of CoG, LoG and BoS to human postures and movement • Describe the forces that act on the body • Describe the three orders of levers and how they can be demonstrated within the body University of Hertfordshire - MS 2011/12

  3. Learning Outcomes • Explain mechanical advantage and benefit to physiotherapists • Explain Newton’s Laws of motion • Analyse movement in relation to Newton’s Laws of motion University of Hertfordshire - MS 2011/12

  4. What makes us move? • Muscles contracting (force) to over come the weight of a limb (load) for movement to occur at a joint (axis) University of Hertfordshire - MS 2011/12

  5. Elbow Example • Where is the axis of movement? • What is force M? • What is force W & F? University of Hertfordshire - MS 2011/12

  6. Knee Example • Where is the axis of movement? • What is force M? • What is force W? M W University of Hertfordshire - MS 2011/12

  7. Internal v External forces • What do the Internal forces acting on the body consist of ? • What forces will work externally on the body? University of Hertfordshire - MS 2011/12

  8. Force description • When representing a force diagrammatically we use arrows • Longer the arrow the greater the magnitude of the force • The direction the arrow points is the direction of the force • The other end of the arrow is the point of application of the force University of Hertfordshire - MS 2011/12

  9. Force analysis • There is usually a combination of forces acting on the body – so how can we determine which way movement will occur? • Look at the following examples and determine which way the movement will occur University of Hertfordshire - MS 2011/12

  10. 1. • The deltoid muscle has fibres which run in three directions, what will the resultant movement of the arm be when all of the portions of the deltoid muscle work together? University of Hertfordshire - MS 2011/12

  11. 2. • Resolve these forces. • Which way will both examples move? University of Hertfordshire - MS 2011/12

  12. Clinical practice… University of Hertfordshire - MS 2011/12

  13. Levers • Much of the time the internal forces working within the body (e.g. muscles) are working on a lever(e.g. long bones). • When considering levers the moment of force is an important factor • This is the rotary effect that occurs due to there being a fulcrum (fixed point) around which the movement occurs. University of Hertfordshire - MS 2011/12

  14. Elbow Example FORCE m LOAD m = MOMENT ARM University of Hertfordshire - MS 2011/12

  15. The Orders of Levers • 1st order • 2nd order • 3rd order University of Hertfordshire - MS 2011/12

  16. Using Mechanical Advantage • The length of the lever arm between the fulcrum and force (force arm) determines mechanical disadvantage • Hold a weight. Abduct your arm with your elbow in full extension and then in 90° flexion. Which movement is easier? Why? • How could you make performing elbow flexion more difficult? University of Hertfordshire - MS 2011/12

  17. Mechanical Advantage • Imagine you are testing a patient’s strength in their Quads by manually resisting knee extension. • How can you use mechanical advantage to your favour? • How could you make an exercise for the Quads harder? University of Hertfordshire - MS 2011/12

  18. Stability- Task • Adopt each of the following positions and rank them from most to least stable • Standing, sitting, kneeling, lying • Can you account for/justify this ranking? • Can you modify each of these positions to make them more or less stable? Justify your answers. University of Hertfordshire - MS 2011/12

  19. Centre of Gravity • The point about which the weight of all the body segments is evenly distributed • In the anatomical position it is anterior to S2 • The Line of Gravity (LoG)is a vertical line through the CoG University of Hertfordshire - MS 2011/12

  20. Base of Support • Surface area of the part that is involved in supporting the object • Consider walking aids! • Think about the relationship between the line of gravity and the base of support • Which factors influence the stability of a body? University of Hertfordshire - MS 2011/12

  21. Stability of a body depends on….. • The surface area & stability of the BoS • The location of the LoG within the BoS • The height of the CoG above the BoS • The mass of the body University of Hertfordshire - MS 2011/12

  22. Equilibrium - Task • All stand with legs slightly apart, get a partner to your left to move & push you from behind (carefully) • What happens? • Why? • Now repeat in step stance (one leg in front and sideways of other) • What happens? • Why?

  23. Conclusion • Look back over the learning outcomes for this session and the associated study required. • Make sure you are happy that they have been met and understand the concepts introduced and discussed University of Hertfordshire - MS 2011/12

  24. ANY QUESTIONS ?? Thank you for listening & participating University of Hertfordshire MS - 2011/12

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