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

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.

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!

What is a Force?  A force gives energy to an object. Whenever two objects touch, forces are involved.

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

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.

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.

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.

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

Inertia & the Golf Swing  How does inertia affect the golf swing? Golf Ball Club Head

Law 2: Law of Acceleration  When a force acts upon a mass, the result is acceleration of that mass. a. The greater the force, the great the acceleration. b. The smaller the mass, the greater the acceleration. c. The mass will accelerate in the direction the force is applied. F = m x a (force) (mass) (acceleration)

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

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.

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.

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.

Law 3: Action - Reaction Law  These two forces always work in pairs, and are opposite in direction and equal in size.

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

The forces will be equal when the truck crashes into the car. Since the car is smaller, the car will have a greater acceleration.

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.

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).

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

Motion

Types of Motion General Motion Curvilinear Motion Angular Motion 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

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

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

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

Projectile Motion Any object released into the air is termed a projectile.

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

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.

Gravity

Gravity

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

Angle of Release The angle of release of a projectile determines the flight path. a.If the angle of release is high, the projectile has a longer flight time but decreased distance. a.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.

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

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

Height of Release The greater the height of release the greater the distance gained

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

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.

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

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).

Stability & Balance

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

Centre of Gravity 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 RUNNING EXAMPLE 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

Increasing Stability Stability is increased when Centre of Gravity is lowered

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

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

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

Biomechanics of Torque (Rotational Force)

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)

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

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

Parts of a Lever Levers consist of 3 parts; a)Resistance b)Force c)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)

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

First Class Levers

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

Second Class Levers

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

Third Class Levers

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

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!

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

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

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.

Handball

Shot Put

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

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. to allow muscles to be contracted with max force.

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

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 If timing is out of order movement will lack co-ordination and force generation is lessened or lost

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