Levers in the Human Body

1. Levers in the Human Body

3. First Class Levers • Axis is between the other two components • F A R • Teeter Totter • Either speed or strength • Only lever that can be balanced • Only lever that can have a mechanical advantage equal to one • Can have a mechanical advantage of less than or greater than one

4. Classes of Levers1st class • The fulcrum (axis) lies between the effort and the load

5. Classes of Levers1st class • As the fulcrum moves toward the load the mechanical advantage increases and the load becomes easier to move but its range of motion and distal end speed decreases. • As the fulcrum moves towards the force the range of motion and the distal end speed increases but the mechanical advantage decreases.

6. Classes of Levers1st class • A first-class lever is a lever in which the fulcrum (axis) is located between the input effort and the output load. In operation, a force is applied (by pulling or pushing) to a section of the bar, which causes the lever to swing about the fulcrum, overcoming the resistance force on the opposite side. • The fulcrum may be at the centre point of the lever as in a seesaw or at any point between the input and output. This supports the effort arm and the load.

7. Class 1 Levers

8. AnatomicalFirst Class Lever • Tilting the Head Backwards • R A F

9. Second Class Levers • Resistance is between the other two components • A R F • Wheelbarrow • Built for strength • Mechanical advantage is greater than one

10. Classes of Levers2nd class • The fulcrum (axis) is at one end, the effort at the other end and the load lies between the effort and the fulcrum

11. Classes of Levers2nd class • As the load moves toward the fulcrum the mechanical advantages increases and it becomes easier to move but its range of motion and speed decrease. • As the load moves towards the force the range of motion and speed increases but the mechanical advantage decreases.

12. Classes of Levers2nd class • In a second class lever the input effort is located at the end of the bar and the fulcrum (axis) is located at the other end of the bar, opposite to the input, with the output load at a point between these two forces.

13. Class 2 Levers

14. AnatomicalSecond Class Lever • Raising up on the toes • F R A (blue picture)

15. Third Class Levers • Force is between the other two components • A F R • Shoveling • Built for speed • Mechanical advantage is less than one

16. Classes of Levers3rd class The fulcrum (axis) is at one end, the load at the other end and the effort lies between the load and the fulcrum

17. Classes of Levers3rd class • As the force moves toward the fulcrum the mechanical advantage decreases and the load becomes more difficult to move but its range of motion and distal end speed increases. • As the force moves towards the load the range of motion and the distal end speed decreases but the mechanical advantage increases.

18. Classes of Levers3rd class • For this class of levers, the input effort is higher than the output load, which is different from second-class levers and some first-class levers. • However, the distance moved by the resistance (load) is greater than the distance moved by the effort. Since this motion occurs in the same length of time, the resistance necessarily moves faster than the effort. • Thus, a third-class lever still has its uses in making certain tasks easier to do. In third class levers, effort is applied between the output load on one end and the fulcrum (axis) on the opposite end.

19. Class 3 Levers

20. AnatomicalThird Class Lever R F A

21. Levers in the Human Body • The human body is built around a sturdy frame called the skeleton. • Muscles are attached to the skeleton and generate movement. • Many levers exist within the skeletal structure. • Nature has designed the human body for movement rather than maximising force.

22. Levers in the Human Body • The forearm is a classic example of nature's way of maximising motion rather than force. The biceps is a muscle that flexes the arm. Tendons attach this muscle close to the elbow.

23. Levers in the Human Body • The forearm is an example of a third order lever. Identify the fulcrum, load and effort. The effort is where the muscle is attached. You can flex your biceps and find where they attach on your forearm. • What type of lever is the forearm?Is it designed to maximise distance or force?. • In nature why is it more important to multiply the distance rather than the force?.

24. Levers in the Human Body • The thigh muscles (quadraceps) are attached to the shin bone (tibia) just below the knee joint. Look at the athlete on the right as he performs the leg extension exercise. • Identify the fulcrum, load and effort of this particular lever system. • What type of lever is this? • The muscle generates movement by shortening and pulling on a bone. Compare the amount the muscle shortens with the amount of movement generated in the lower leg. Is this lever system designed for force or speed multiplication?

25. Levers in the Human Body The action associated with kicking a soccer ball involves a number of levers working together. Consider the kicking motion shown on the right.

26. Levers in the Human Body • The kicking action is animated on the right. • What muscles are involved to start the femur moving? Where are these muscles attached? • Identify all the levers involved. • What type of lever is each?

27. Levers in the Human Body • The forearm is controlled by two opposing set of muscles. The movement of the forearm is shown on the right. • What type of lever is formed when the biceps contract? • What type of lever is formed when the triceps contract? • Why are both sets of muscles attached so close to the elbow (fulcrum)?

28. Levers in the Human Body • The picture on the right shows the bone structure of the leg. Sitting down on a chair raise your shins to a horizontal position. Your thigh muscle tenses in order to lift the lower part of the leg. • Using the shin as an example identify the fulcrum, load and effort. • What type of lever is this?Is this the best type of lever to use for the shin? Explain.

29. Levers in the Human Body • What type of lever is this? • Third order lever. Is this the best type of lever to use for the shin? Yes. Explain. • To maximize movement this is the ideal lever. With the effort close to the fulcrum we can multiply the distance the load travels. Notice how the thigh muscle is attached just below the knee joint. Small changes in muscle length result in large changes in the distance travelled by the load. • The thigh muscles are a very strong group of muscles. A third order lever gives no mechanical advantage and therefore strong muscles are needed to generate significant forces resulting in leg movement.

30. Human Leversexercises • The picture on the right shows the bone structure of the hand. • Identify the types of levers present and label the fulcrum, load and effort. • What do these levers multiply?

31. Human Leversexercises • The picture on the left shows the bone structure of the foot.What muscle controls the movement of the foot as we jump off the ground?Where is the Achilles' tendon attached? • Identify the type of lever present and label the fulcrum, load and effort. • What does this lever multiply?

32. Human Leversexercises • Look at the ball and socket joint of the femur and hip on the right. Look at the attachment of the muscle to the femur. • What type of lever is this? • What advantage does this lever offer?

33. The footSecond order lever in action. • By now it should be obvious that most of the levers found in the body are third order levers. Nature sacrifices mechanical advantage for an increase in distance travelled. Since the effort is placed so close to the fulcrum a great deal of force is needed to lift any significant load. • The foot however is an example of a second order.The foot is used to spring the body off the ground. Upon landing the foot is gently placed on the ground by the contraction of muscles at the front of the lower leg.

34. Human Leversexercises • Look at the animation above.During stage "A" the foot springs the body off the ground.What type of lever does the foot represent during stage "A"?Does this lever give a mechanical advantage or is it a distance multiplier? Explain.Label the load, fulcrum and effort.During stage "B" the foot lands on the ground.What type of lever does the foot represent during stage "B"? Does this lever give a mechanical advantage or is it a distance multiplier? Explain. • The gastrocnemius is a very powerful muscle, one of the strongest muscles in the body. Why does this muscle need to be so powerful?

35. First class levers in the Human Body • A lever that has its fulcrum (point of support or axis of rotation) between the point of resistance (load) and the point of effort (applied force). • In the human body, a first class lever is used when the head is raised off the chest.

36. Summary Classes of levers. (a) In a first-class lever, the fulcrum (F) is set up between the resistance (R) and the effort (M). (b) In a second-class lever, the resistance is between the fulcrum and the effort. (c) In a third-class lever, the effort is between the fulcrum and the resistance.

37. Summary

38. Forces in Your Body • When you walk, there is 2 to 3 times your body weight transmitted through each foot. • When you run, this is 7 to 8 times • The foot has 26 bones – everything must be functioning correctly to avoid injury • E.g. flat feet

39. Forces in Your Body

40. Forces in Your Body • When you sit with bad posture, there is a 200% increase pressure in your spine. • Reaching for your toes is a 300% increase • Human movement is very complex. There may be dozens of joints and muscles working to achieve a desired movement.