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Maximum Force and Levers

Maximum Force and Levers. Principle 2 – Maximum Force. The production of maximum force requires the use of all possible joint movements that contribute to the task’s objective. Principle 3 – Maximum Force.

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Maximum Force and Levers

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  1. Maximum Force and Levers

  2. Principle 2 – Maximum Force The production of maximum force requires the use of all possible joint movements that contribute to the task’s objective.

  3. Principle 3 – Maximum Force The production of maximum velocity requires the use of joints in order – from largest to smallest.

  4. Impulse, Impact, and Momentum • Momentumis the amount of motion a body possesses • Impulseis the application of an external force over a short time period • Impactis the application of an external force • Momentum is created by an impulse and is lost through impact • Impulse and impact are both associated with bodies that are changing their state of motion by experiencing large accelerations over relative short time periods • Collision or impact skills can sometimes manipulate the time of contact and reduce the magnitude of the external force • To increase impulse, a sprinter must increase the net external force per step

  5. Applications of Maximum Force • What are points in sports you play that you use maximum force? • What are points in your day to day life that you use maximum force? • How does it relate to Stability?

  6. Levers • Simple machines that augment the amount of work done by an applied force • A rigid body (i.e., long bone) that rotates about a fixed point (i.e., joint) called a fulcrum (F) • Acting on the lever is a resistive force (R, i.e weight of a limb segment) an an applied force (AF, i.e., muscle contraction).

  7. Levers • What do levers have to do with human movement? • EVERYTHING! • Levers are rigid bars (in the body, bones) that move around an axis of rotation (a joint) or fulcrum • Forces (supplied by muscles) cause the movement to occur

  8. Lever Functions • Magnify a force • A simple crow bar • Increase speed and range-of-motion (ROM) • Small amount of muscular contraction proximally can produce lots of movement distally

  9. Lever Functions • Balance torques • A triple beam scale • Change direction of force • A seesaw or a pulley of a weight machine

  10. Lever Types • First, second, and third class • Arrangement of the applied force, the fulcrum, and the resistance determines the classification • Classification determines the lever’s strengths and weaknesses

  11. Three classes of levers: a. first class (teeter-totter) b. second class (wheelbarrow) c. third class (screen door with a spring closing)

  12. First Class • FAL • When the axis is closer to force than the load/resistance • Produces speed and ROM • Helps produce Power • About 25% of the muscles in your body operate as first class levers Force Resist. Axis

  13. L F Axis L F Axis

  14. Force Resist. Example: Neck extension Axis

  15. Second Class • ALF • Very few occurrences in the body • Gain resultant force (you can lift more), lose distance Force

  16. Force Resist. Axis

  17. Third Class • AFL • As much as 85% of the muscles in the body function as third class levers • Usually produce speed at the expense of force • Greater lever length = greater speed (ex.) Force

  18. D D Factors affecting the moment of force A. Balanced teeter-totter B. Increasing the moment arm by leaning backwards C. Increasing the applied force by adding a friend

  19. Calculating Moments of Force • Moment arm is the shortest (perpendicular) distance from the axis of rotation to the line of action of the force • Moment of force is influenced by the magnitude of moment arm and the magnitude of the force Moment of Force = Moment Arm x Force By grasping the wrench at the end (A) a greater torque is generated because the moment arm is greater than in (B)

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