Maximum Force and Levers

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

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

Impulse, Impact, and Momentum Recall: Impulse, Impact, and Momentum Recall: Impulse, Impact, and Momentum Momentum is created by an impulse and is lost through impact 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 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 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 To increase impulse, a sprinter must increase the net external force per step

Manipulating Time of Contact: Gymnastics Flexing the joints in lower limbs (ankles, knees, and hips) increases the time over which external impact forces from the ground act on their bodies. This works to decrease the force!

Levers Simple machines that augment the amount of work done by an applied force 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) 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) and an applied force (AF or “effort”, i.e., muscle contraction). Acting on the lever is a resistive force (R, i.e weight of a limb segment) and an applied force (AF or “effort”, i.e., muscle contraction).

Levers What do levers have to do with human movement? 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 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 Forces (supplied by muscles) cause the movement to occur

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

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

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

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

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

Axis F L L F

Force Resistance/Load Examples of First Class Levers

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

Force Resist. Axis

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

Moment Moment of Force: The tendency of a force to twist or rotate an object. Dependent on the force applied and the Moment Arm.

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 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)

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