BIOMECHANICS PSE4U1

Grinding the Crack – Jeb Corliss What is biomechanics? Grinding the Crack – Jeb Corliss https://www.youtube.com/watch?v=TWfph3iNC-k Biomechanics is the science of human movement. It is the study of internal forces produced by muscles and tendons working against external forces such as gravity, air resistance, water resistance and friction. Biomechanics helps coaches, trainers, and technologists to evaluate and improve the performance of athletes by modifying technique and equipment.

Biomechanical principles include… Forces Stability Newton’s Laws Impulse Collisions Momentum Acceleration Leverage Linear Motion Curvilinear Motion Angular Motion Projectile Motion Drag Force Lift Force Spin Axes and Planes

Biomechanical Terms Mass Force Pressure Energy Torque Amount of matter in an object Force Any action that changes the motion of an object or deforms it. Pressure Ratio of force to the area over which the force is applied Energy Capacity of the body to perform work Kinetic energy Potential energy Torque A twisting, turning, or rotary force that causes angular acceleration

Biomechanical Terms (cont.) Speed Change in distance over time (d/t) Velocity Speed and direction of the body (displacement/time) Acceleration Change in velocity (Vf-Vi/time) Angular velocity Degrees of rotation/time Angular acceleration Change of angular velocity

Biomechanical Terms (cont.) Gravity The force that pulls all objects toward the centre of the earth. The acceleration of an object due to gravity is 9.8m/s2 Friction The drag force that occurs when in two surfaces contact with or slide over each other. Power Amount of work accomplished in one unit of time (Force/time)

Movement Axes There are three axes around which movement can occur. 1.Vertical 2.Horizontal 3.Antero-posterior When standing: The vertical axis runs from head to foot through the body’s centre of gravity. The horizontal axis runs from side to side through the body’s centre of gravity. The antero-posterior axis runs from front to back through the body’s centre of gravity.

Forces “something that causes an object to be deformed or moved.” (Roberts & Falkenburg, 1992) Force can: Get objects moving Stop objects moving Change the direction of a moving object Change the speed of a moving object Balance another force to keep an object still

External Forces & Internal Forces Internal forces are generated by muscular contractions or motors. External forces include: Gravity Friction Air resistance Ground reaction force Point of application Direction Resultant action Get objects moving Stop objects moving Change the direction of a moving object Change the speed of a moving object Balance another force to keep an object still

Forces Production of Force The actions of muscles. The stronger the muscles, the more force the body can produce. Application of Force The force of an object is most effective when it is applied in the direction that the object is intended to travel. Absorption of Force The impact of a force should be gradually reduced (“give with the force”) and spread over a large surface.

Impulse Impulse = Ft N/Sec When a force is applied to an object, the magnitude of the force (F) multiplied by the time (t) that the force is applied, is called the impulse. Impulse = Ft N/Sec The greater the applied impulse, the greater the increase in velocity a.k.a. acceleration. Impulse depends on: The time that the force acts on the target, and the size of the force applied

Momentum Momentum = Mass x Velocity

TYPES OF MOTION 1. Linear Motion The progression of a body in a straight line with all parts moving in the same distance, direction, and speed

2. Angular Motion Angular motion is produced by the application of a force acting at some distance from an axis, that is, by torque. Angular motion is far more common than linear motion in sport because angular motion is occurs whenever levers (bones) rotate around axes (joints).

Moment of Inertia Following a series of rapid somersaults in a tight position, a gymnast does a forward flip with her body extended. By opening up, the gymnast has increased the moment of inertia , resulting in a decrease in angular velocity. Moment of inertia describes the distance a part of an object or body is away from its axis and influences an objects speed of rotation.

3. Curvilinear Motion An object exhibiting curvilinear motion travels in a parabolic trajectory. All projectiles, which are objects that have a flight phase, have parabolic trajectories.

4. General Motion General motion is a combination of linear, angular, and curvilinear motion .

Inertia - Newton’s First Law “a body will continue in a state of rest or in a straight line of uniform motion unless acted on by an external force.” Inertia is the resistance of an object to change. An object in motion tends to stay in motion. An object at rest will remain at rest, unless acted upon by a outside force.

Acceleration - Newton’s Second Law “When a force acts on an object, the object accelerates in the direction in which the force is acting.” Acceleration = The final velocity minus the initial velocity divided by time. A = (v f– vi ) t A force applied to a body causes an acceleration of that body of a magnitude proportional to the force, in the direction of the force, and inversely proportional to the body’s mass.

Reaction - Newton’s Third Law “for every action there is an equal and opposite reaction.”

Stability & Balance Stability is optimized when: The centre of gravity is low The base of support is large The centre of gravity is located over the base The mass is large Headstand Handstand Elbowstand?

Leverage A lever is a rigid bar that rotates around an axis. Lever components Fulcrum - centre or axis of rotation Force arm - distance from the fulcrum to the point of application of the force Resistance arm - distance from the fulcrum to the weight on which the force is acting

Levers First class – the fulcrum is between the resistance and the force. E.g. Teeter-totter Second class – the resistance is between the fulcrum and the force E.g. Wheel-barrow Third class – the force is between the fulcrum and the resistance E.g. Shovelling

Levers in the human body Every moveable bone in the human body, acting alone or in concert with others, is part of a lever system that facilitates movement. The distance between a muscle’s insertion and it’s proximal joint is the force arm, and the distance between the joint and the weight to be overcome acts as the resistance arm. Most levers in the human body are 3rd class.

The Principle of Summation of Force Sequential Summation of Force When the maximum force is required: All body segments that can contribute to an action should be involved. The action should start with the largest body segments first. Each body segment should be sequentially stabilized in order to transfer momentum to progressively smaller body segments.

The Principle of Summation of Force Simultaneous Summation of Force When a strong, precise action is required, all body segments around the target segment should be simultaneously stabilized to produce the most focused action possible.

Types of Collisions Perfectly elastic: neither object loses its shape Partially elastic: an object loses its shape and then regains it. Inelastic: both objects are permanently deformed.

Projectile Motion A projectile is any body or object that has a flight phase. Projectiles travel in a parabolic trajectory. The trajectory of a projectile is determined by: The angle of release Drag force Lift force Type of spin Coefficient of Restitution Fluid forces such as turbulence and flow

Drag Force Drag is resistance - a force that slows the motion of a body through a fluid (air or water). Athletes can reduce drag by using techniques (such as skiing in a ‘tuck’), equipment (tear-drop helmets and boot spoilers) and/or clothing (rubber suits) . Streamlining reduces form drag.

Direction of fluid flow Lift Lift is a force that acts perpendicular to fluid flow. Direction of fluid flow Lift force

Spin Spin is the rotation of a body or object. Torque is the force which creates spin. The type and amount of spin depends on how much torque is applied and where it is applied. TOPSPIN SIDESPIN BACKSPIN

Spin & Bounce Spin influences the angle of reflection following a bounce. How does topspin affect the angles of incidence and reflection? What about backspin and sidespin?

Coefficient of Restitution (C 0f R) Coefficient of restitution is a measure of an objects “bounciness” or elasticity. Bounce is influenced by: Type of material Heat of material Type of implement/surface Impulse of implement C of R = height of bounce height of drop

Analysis of Movement Biomechanical analysis of technique requires breaking down all of the movements into phases

Phases of Movement Most sport skills involve a preparatory phase, a movement phase and a follow through phase. Many begin with a stance phase and end with a recovery phase.

Movement Phases (cont.) 1. Stance Allows the athlete to assume a comfortable and balanced body position from which to initiate the sport skill. 2. Preparatory Phase Often called the cocking, or wind up phase, is used to lengthen the appropriate muscles so that they concentrically contract in the next phase

Movement Phases (cont.) Sometimes called the acceleration, motion or contact (is the action of the skill) 4. Follow Through Begins immediately after the climax of the movement phase in order to bring about negative acceleration of the involved limb 5. Recovery Used to regain balance and positioning to be ready for the next sport demand

The Tennis Serve D. C. B. A. A. Stance: Player stands behind baseline with his ball hand facing the net B. Preparatory Phase: Player’s racket arm and shoulder are cocked back C. Movement: The arm rotates forward for the racket to make contact; the racket arm continues to rotate and slows until … D. Recovery: …his arm changes direction; his weight shifts forward; and he lunges forward to prepare for the return. D. C. B. A.