12 Seven Principles of Biomechanics PDF

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12.1 Static and Dynamic Systems ● The 7 principles of biomechanics are set forth by the Coaching Association of Canada's National Coaching Certification Program (NCCP) ● 7 principles can be grouped into 4 broad categories: Biomechanical Concept Principles Stability

1. Stability

Maximum effort

2. Production of Maximum Force 3. Production of Maximum Velocity

Linear motion

4. Impulse 5. Direction of Application of the Applied Force

Angular motion

6. Production of Angular Motion (Torque) 7. Conservation of Angular Momentum

● The principles can be understood in the context of 2 systems 1. Static 2. Dynamic ● The 7 principles involve interactions of static and dynamic systems ○ Help to explain how and why certain body characteristics are more desirable ○ Provides professionals feedback to students, athletes, patients or clients

Nature of Static Systems ● Statics: The branch of mechanics that studies objects or bodies in a state of constant, unchanging motion ● The study of statics is related to Newton’s first law of motion (inertia)

Nature of Dynamic Systems ● Dynamics: The branch of mechanics that studies changes in motion of objects or bodies as result of forces applied to it

12.2 Stability (Principle 1) ● Principle 1: The greater the mass, the lower the centre of mass to the base of support, the larger the base of support, and the closer the centre of mass, the more stability increases

● Stability: The quality, state, or degree of being stable and capable of resisting change in motion

Mass ● Mass: Quantity of matter contained within an object or body ● When the force of gravity acts on mass, the resulting quantity is weight ● The greater the mass, the greater the resistance to going from a state of rest to a state of motion and vice versa ● As well, as inertia increases, the effort required to move a body or an object increases

Centre of Mass ● Centre of mass: Imaginary middle point around which the mass of an object is balanced ● Concept of centre of mass is important in the context of resisting rotation

Base of Support ● Base of support: The supporting area beneath an object or body; defined by the points of contact with the support surface ● A broader base of support increases stability ○ E.g. 3-point stance: Crouching and putting one hand on the ground ● The most stable stance is when both hands and feet are in contact with the ground (4-point stance)

Position of the Centre of Mass ● Position of the centre of mass: A position relative to the base of support as defined by the line of gravity ● Line of gravity: An imaginary vertical line that passes through the centre of mass to the ground ● If the position of the centre of mass moves outside the base of support stability will greatly decrease

12.3 Maximum Effort (Principles 2 & 3) ● Many activities require 100% effort to be exerted ● Proper technique is required to avoid injury

Principle 2: Production of Maximum force ● Principle 2: The production of maximum force requires the use of all possible joint movement that contribute to the task’s objective ○ E.g. A 4 year old T-ball player might plant their feet and only use their arms while a professional baseball player bends their knees and twists their body

Principle 3: Production of Maximum Velocity ● Principle 3: The production of maximum velocity requires the use of joints in order — from largest to smallest

12.4 Linear Motion (Principles 4 & 5) Principle 4: Impulse Momentum Relationship ● Principle 4: The greater the applied impulse, the greater the increase in velocity ● Velocity: The rate and direction of motion of an object or body; the change in displacement over time

● Momentum: The quantity of motion contained within an object or body; equal to the product of the object’s mass and its velocity

● Impulse: The application of a force over a period of time; the change in momentum; force multiplied by time

● Impulse-momentum relationship: In the absence of external forces, the total momentum of a given system remains constant (Newton’s 1st Law); any change in momentum is equal to the impulse that it produces

Applications of Principle 4 Fosbury Flop ● High jumpers use a technique called the Fosbury Flop to generate greater impulse off the ground

● While in flight, jumpers can arch their backs and necks to keep as much of their body under the bar at all times, and therefore their centre of gravity

Jump Serve ● The forward running motion of a volleyball server’s body transfers momentum to the ball, giving it much higher velocity

Bobsled ● Bobsledders must apply as much impulse as possible to the sled before they jump in

Principle 5: Direction in Which Movement Usually Occurs ● Principle 5: Movement usually occurs in the direction opposite that of the applied force ● Related to Newton’s 3rd law of motion, which states that for every action there is an equal and opposite reaction

12.5 Angular Motion (Principles 6 & 7) Principle 6: Effect of a Force Acting at some Distance from an Axis ● Principle 6: Angular motion is produced by the application of a force acting at some distance from an axis; that is, by torque

Applications of Principle 6 ● The amount of torque generated depends on 3 factors 1. The magnitude of the applied force 2. The length of the lever arm (the distance from the point of application of the force and the axis) 3. The angle at which the force is applied to the lever arm ● Angle of insertion: The angle at which a tendon (representing the force vector) attaches to the movable bone (the lever arm) ● Tendons typically do not insert on the movable bone at 90 degrees, instead the magnitude of torque generated changes at each stage of movement ● If torque generated at any stage of movement is too high, excessive strain will be placed on the tendon (typically where it inserts)

Principle 7: Conservation of Angular Momentum ● Principle 7: Angular momentum is constant when an individual or object is free in the air

● Angular momentum: The quantity of angular motion contained within an object or body; angular velocity multiplied by moment of inertia

● Angular velocity (rotational velocity): Quantitative expression of the amount of rotation that a spinning object undergoes per unit of time

● Moment of inertia: An object’s or body’s resistance to a change in its rate of angular rotation; the greater the distance of an object or body’s distribution of mass from the axis of rotation, the greater its moment of inertia

Applications of Principle 7 ● Law of conservation of angular momentum: The total angular momentum of a rotation body remains constant if the net torque acting on it is zero ○ E.g. A skater will rotate at a higher velocity if her arms are closer to her rotational axis; her moment of inertia decreases; her angular momentum needs to remain constant...