Sport%20Biomechanics

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Sport Biomechanics

• Understanding how a skill is performed
  mechanically is an important stepping stone to
  understanding how it can be learned.

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Basic Laws of Biomechanics

• Sir Isaac Newton developed three laws to explain
  the relationship between forces acting on a body
  and the motion of the body.

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What is a Force?

• A force is a push or a pull. Forces are measured
  in Newtons. Did you know that forces only exist
  when objects interact!

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What is a Force?

• A force gives energy to an object. Whenever two
  objects touch, forces are involved.

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What is a Force?

• A force can cause acceleration, a change in
  direction or deceleration. A force is NOT
  required to keep an object in motion
• Examples
• -Drag, Friction, Thrust, Gravity, Weight,
  Magnestism

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Law 1 Law of Inertia

• An object at rest will remand at rest unless
  acted upon by some external force.
• The greater the inertia an object has the greater
  the force needed to move it.

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Objects at rest remain at rest unless acted on by a net force. Objects at rest remain at rest unless acted on by a net force.

A lot of inertia! Very little inertia.
Since the train is so huge, it is difficult to change its speed. In fact, a large net force is required to change its speed. Since the baby carriage is so small, it is very easy to change its speed. A small net force is required to change its speed.
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Objects in motion remain in motion in a straight line (unless acted upon by an outside force). Objects in motion remain in motion in a straight line (unless acted upon by an outside force).

A lot of inertia! Very little inertia.
Since the train is so huge, it is difficult to stop it once it is moving. It is difficult to change its speed. In fact, a large net force is required to change its speed. Since the soccer ball is so small, it is very easy to stop it once it is moving. A small force is required to change its speed.
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Law 1 Law of Inertia

• In what sports would a lot of inertia be to the
  athletes advantage?
• -Sumo, Scrumming
• In what sports would a lot of inertia be to the
  athletes disadvantage?
• Sports requiring quick
• change of direction

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Inertia the Golf Swing

• How does inertia affect the golf swing?

Club Head
Golf Ball
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Law 2 Law of Acceleration

• When a force acts upon a mass, the result is
  acceleration of that mass.
• The greater the force, the great the
  acceleration.
• The smaller the mass, the greater the
  acceleration.
• The mass will accelerate in the direction the
  force is applied.

F m x a
(force) (mass) (acceleration)
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Big masses are hard to accelerate. Big masses require big forces to change speed.
Small masses are easy to accelerate. Small masses require small forces to change speed
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Assume that both steam engines below apply the
same amount of force.
A heavy train has a difficult time accelerating. Big masses require big forces to change speed.
When the same force is applied to a less massive train its acceleration is greater. Small masses require small forces to change speed.
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Law 2 Law of Acceleration

• How can we apply this law of acceleration to the
  golf swing?
• - The greater the initial force (contracting
  muscles), the greater the acceleration of the
  club head and the greater acceleration on the
  golf ball on contact.
• - The greater the force, the further the golf
  ball will travel.

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Law 3 Action - Reaction Law

• For every action, there is an equal and opposite
  reaction.
• When we apply a force this is known as an action
  force.
• The object we apply the force to, applies a force
  back, this is a reaction force.

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Law 3 Action - Reaction Law

• These two forces always work in pairs, and are
  opposite in direction and equal in size.

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The forces here are equal and opposite. Neither
the dog nor its owner pulls with greater force.
They pull with the same force in opposite
directions
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The forces will be equal when the truck crashes
into the car. Since the car is smaller, the car
will have a greater acceleration.
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If forces are always equal and opposite, how can
anything move?
Here is a famous problem A horse is pulling on a
cart, and the cart pulls back with the same
amount of force. If all forces are equal, how can
the horse and cart move?
Answer The horse moves because the force he
exerts with his hooves is greater than the force
of the wagon pulling him back.
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If forces are always equal and opposite, how can
anything move?

• What forces act on the cart? The horse pulls it
  forward, and there is a backward force from the
  ground friction. If the horses' pull exceeds the
  friction of the cart, it will accelerate.

Acceleration will occur if one force pair (push
of ground/push of horse) is greater than another
force pair (friction/pull of cart).
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If forces are always equal and opposite, how can
anything move?

• Example 2 If the person's friction forces
  against the floor are greater than the
  refrigerator's friction forces, the fridge will
  accelerate.

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Motion
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General Motion
Angular Motion
Types of Motion
Curvilinear Motion
Linear Motion
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Linear Motion

• When all parts of the body move in a straight
  parallel lines (same distance in same time).
• Examples
• -Dropping a ball
• -Sliding in to first base
• -Tobogganing down a hill

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Curvilinear motion

• When all parts of the body move in a curved path
  along parallel lines.
• Examples
• -free fall sky diving
• -path of a tennis serve
• -flight of golf ball

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Angular Motion

• Rotation about an axis that can be either
  internal or external.
• Examples
• -swinging around a high bar
• -a bicep curl
• -a golf swing

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General Motion

• Linear motion of the body as a result of angular
  motion of other parts of the body.
• Examples
• Cycling
• Swimming
• Kayaking

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Projectile Motion

• Any object released into the air is termed a
  projectile.

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All projectiles have a flight path and flight
time depending on how they affected by the
variables below.

• Gravity
• Air Resistance
• Angle of Release
• Speed of Release
• Height of Release
• Spin

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Gravity

• Gravity acts on a body to give it mass.
• The greater the mass of an object the greater the
  influence of gravity upon it.
• What is the effect of gravity on a projectile?
• - It decreases the height a projectile can
  attain.

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Gravity
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Gravity
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Air Resistance

• Air resistance acts on the horizontal component
  of a projectiles path.

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Angle of Release

• The angle of release of a projectile determines
  the flight path.
• If the angle of release is high, the projectile
  has a longer flight time but decreased distance.
• If the angle of release is low, the projectile
  has less flight time but increased distance
• However if the angle is too low, distance is
  poor.

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Angle of Release

• How is distance and height manipulated in golf
  for the best shot?
• - Angle of club head.

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Speed of Release

• Velocity (speed of motion) of release will
  determine the size of the flight path.

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Height of Release

• The greater the height of release the greater the
  distance gained

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Spin

• There are two main types of spin
• 1. Top spin- distance is decreased with
  topspin.
• 2. Back spin- distance is increased with
  backspin.

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Back Spin

• A backspin shot creates a region of low pressure
  on top of the ball and a region of high pressure
  below. As a consequence, the ball floats suddenly
  thereby increasing the distance attained.

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Topspin

• Q. So how does Topspin work?
• A. A topspin shot creates a region of high
  pressure on top of the ball and a region of low
  pressure below. As a consequence, the ball dips
  suddenly thereby decreasing the distance attained

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A golf ball acquires spin when it is hit.
Backspin is imparted for almost every shot due to
the golf club's loft (i.e., angle between the
clubface and a vertical plane). A spinning ball
deforms the flow of air around it similar to an
airplane wing a back-spinning ball therefore
experiences an upward force which makes it fly
higher and longer than a ball without spin. The
amount of backspin also influences the behavior
of a ball when it impacts the ground. A ball with
little backspin will usually roll out for a few
yards/meters while a ball with more backspin may
not roll at all, even backwards. Sidespin occurs
when the clubface is not aligned perpendicularly
to the plane of swing. Sidespin makes the ball
curve left or right a curve to the left is a
draw, and to the right a fade (for right-handed
players). Accomplished golfers purposely use
sidespin to steer their ball around obstacles or
towards the safe side of fairways and greens. But
because it's sometimes difficult to control or
predict the amount of sidespin, balls may take an
undesirable trajectory, such as hook to the left,
or slice to the right (for right-handed players).
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Stability Balance
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Centre of Gravity

• The point in the body about which all parts of
  the body are in balance or the point at which
  gravity is centred
• COG is not confined to one location, as the body
  moves so the COG moves with it in the direction
  the movement occurs

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Centre of Gravity
RUNNING EXAMPLE

• This runner has an upright trunk
• Level pelvis
• Centre of gravity is well behind the contact
  point of the leading foot
• This allow progressive loading of the leading leg

• With a trunk leaning forwards
• The centre of gravity is almost directly over
• the foot as it lands
• The loading on the foot, ankle, knee,
• pelvis rises steeply

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Increasing Stability

• Stability is increased when Centre of Gravity is
  lowered

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Increasing Stability

• Stability is increased when the line of gravity
  falls within the BOS (Base of Support

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Increasing Stability

• Stability is increased with increased mass
• Why?
• Greater inertia requires more force by an
  opponent to move the line of gravity
• Eg. Rugby a bigger forward pack has an
  advantage in scrums

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Increasing Stability

• Stability also is increased when BOS is extended
  in the direction of an oncoming force
• Stability is increased when the line of gravity
  is moved towards an oncoming force

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Biomechanics of Torque (Rotational Force)
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Biomechanics of Torque

• Rotational movements play an important part in
  all sports skills
• Rotation can involve
• -the whole body (diving, gymnastics) -objects
  (pitching or bowling a ball)
• -the body and equipment as levers (batting, golf)

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Axis of Rotation

• The axes of rotation of the body act through the
  COG
• There are 3 axes of rotation
• Longitudinal eg pirouette
• Transverse - eg forward roll
• Sagittal - eg cartwheel

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Levers

• Levers are designed to allow either a greater
  resistance to be moved with a given force
• Or to increase the velocity (speed) at which an
  object can be moved using a given force

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Parts of a Lever

• Levers consist of 3 parts
• Resistance
• Force
• Fulcrum
• The distance from where a force is applied to the
  fulcrum is called the force arm (FA)
• The distance from where a resistance acts to the
  fulcrum is called the resistance arm (RA)

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First Class Lever

• The fulcrum lies between the resistance and the
  force
• FA shorter than RA favours speed and range of
  movement
• FA longer than RA favours force output

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First Class Levers
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Second Class Lever

• The resistance lies between the pivot and the
  force
• The force arm and the resistance arm are on the
  same side of the lever
• The FA is always longer than the RA

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Second Class Levers
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Third Class Lever

• The force lies between the resistance and the
  fulcrum
• The FA is shorter than the RA
• In third class levers, the force applied is
  always greater than the resistance

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Third Class Levers
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Torque

• As all levers produce rotation about an axis,
  they also produce torque.
• Torque is defined as a turning force
• T F x D
• Torque Force x Distance
• The greater the force applied to a given force
  arm the greater the torque
• The longer the force arm with a given force
  applied the greater the torque

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Initiating Rotation

• In order to initiate rotation on any object, or
  human body an eccentric force must be applied
• An eccentric force is a force applied away from
  the COG
• Apply this principle to explain how a pitching
  wedge works!

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Angular Velocity and Speed of Rotation

• Angular Velocity is the rate of spin of an
  athlete or object as they move in a particular
  direction
• Speed of Rotation is how quickly parts of an
  object or athlete move in a rotational movement

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Angular Velocity and Speed of Rotation

• Speed of rotation of an object increases the
  further it is away from the axis of rotation
• Speed of rotation of an object increases the
  greater the angular velocity
• Speed of rotation of an object is a product of
  angular velocity and the radius of the object
  from the axis of rotation

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Force Summation

• As we know, in order to generate momentum a force
  must be applied to a body
• An athlete is able to achieve a maximum velocity
  or force by the transfer of momentum through
  successive body part movements.

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Handball
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Shot Put
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Force Summation

• Rule 1 Use All Body Segments
• To maximise muscular force we want to use as
  many body segments as possible.

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Force Summation

• Rule 2 Stretch Out
• Before we begin the sequence of body movements
  we should stretch muscles out to their optimal
  length
• to allow muscles to be contracted with max
  force.

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Force Summation

• Rule 3 Sequencing of Body Segments
• Generally we move larger muscle groups first and
  smaller muscle groups last
• Force generated by the larger muscle is groups
  passed on to the smaller ones

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Force Summation

• Rule 4 Timing of Body Segments
• To produce max force we need to ensure that the
  right body segment is adding to the overall force
  at the right time
• If timing is out of order movement will lack
  co-ordination and force generation is lessened or
  lost

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Force Summation

• Rule 5 Full Range of Motion
• We need to move body segments through the
  greatest range of motion that we can.
• Greater the range of motion, the higher the speed
  of the extremities on release/contact