Biomechanics

• “Describe how functional anatomy and biomechanical principals relate to performing a physical activity”

• Coaching movement• Understanding movement• Optimising movement• Russian Gynastics

Biomechanics

Section 1: Forces and Levers

1.2 What is a force?

A force is defined as a push or a pull

Movement Term

Description Example

Translation Moves from A → B

A golf shot. It starts on the tee and finishes on

the fairway

Rotation If the force applied is not

through the COG the object will

rotate

Putting spin on a volleyball

serve

Deformation The object loses shape on impact

A squash ball being hit

1.3 Centre of GravityThe main force acting on all parts of the body

is gravity.

We can define the COG as follows:The point in the body at which all parts of the

body are in balance OR the point at which gravity is centred.

When we stand in the anatomical position, our COG is located around the hip region.

Why is COG lower in women than men?More mass is concentrated around the hips

and below in women. This gives advantages ion sports requiring balance e.g. beam work in gymnastics.

The Axes of Rotation

Axes of Rotation Sporting Examples

Longitudinal Pirouette in danceTwist in diving

Spinning in ice-skating

Transverse Forward/backward somersault

Forward/backward roll

Sagittal CartwheelCricket delivery

Barani or free cartwheel

1.4 LeversA lever consists of three parts1. Resistance2. Effort3. Fulcrum or pivot

Levers perform two main functions:1. To increase the resistance that can

be moved with a given effort, e.g. a crowbar.

2. To increase the velocity at which an object will move with a given force. Golf club

Class Illustration Definition Examples

First The fulcrum lies between the effort and

the resistance

See sawCrowbarHammer

pulling out a nail

Second

The resistance lies between the fulcrum and the point of effort

WheelbarrowOpening a

door by the handle

Rowing a boat

Third The effort lies between

the resistance

and the fulcrum

Biceps curlMost limbs of the body

Revision

Sporting Movement Axis of rotation

One handed cart wheel Sagital

Backward somersault Transverse

Rotation phase in discus Logitudinal

A twist in a dive Longitudinal

Backward roll Transverse

• The human body consists of mainly 3rd class leavers. Why?

• So that we can increase the velocity at which an object can move with given amount of effort. This is why golf clubs, tennis racquets allow us to hit the ball hard.

• Define the C.O.G • The point at which gravity is centred

• An oar in a rowing boat is a First class leaver

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Biomechanics

Section 2: Motion

3.2 Newton’s Laws of Motion

[A] Law 1An object at rest tends to remain at rest unless acted

upon by some external forceThis is known as inertia

Which has more inertia? Why?The 175kg weights have more inertia because it has a

greater mass

Having a great deal of inertia can be advantageous in some sporting situations. How?

If you have a lot of inertia you can be difficult to move e.g. in a rugby scrum, wrestling, judo

Of course having a lot of inertia has disadvantages as well in sporting situations. How?

If you have a lot of inertia, you require a lot of force or effort to get you moving. It can also mean a decrease in agility.

[B] Law 2If a table tennis ball, tennis ball and bowling ball are each hit

or bowled with the same amount of force, which one accelerates the most? Why?

The table tennis ball because it is lighter.

If the tennis ball is hit with gradually increasing force, what happens to its acceleration?

The acceleration will increase with increasing force.In summary, we can say:A. The greater the force, the greater the accelerationB. The smaller the mass, the greater the acceleration when a

constant force is applied.C. The mass will accelerate in the direction the force is

applied.

These statements can be summarised by an equation:Force = mass X acceleration

F = ma

How could you apply Newton’s 2nd Law to sporting situations?The harder you hit the ball, the faster and possibly further it

will travel. For example, swinging a golf club slowly with force gives the golf ball less force hence acceleration than if you swung the golf club forcefully.

[C] Law 3When we apply a force to something it is known as action

forceThe object we apply a force to, applies a force back, a

reaction force

What other example can you think of? When a ball is bounced, it bounces back in a direction

opposite to that in which it was dropped.If these forces are equal, why is earth not pushed backward

when we drive out of the starting blocks in a 100 metre race?

The earth has a huge mass and therefore huge inertia. We cannot generate enough force to overcome this inertia.

Action

Reaction

Action

Reaction

Action

Reaction

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3.5 MomentumWe can rewrite Newton’s First Law to include

momentum: An object that is moving will continue to move

in the direction the force was applied until another force is applied.

[A] Linear MomentumMomentum can be calculated via an equation:

Momentum = mass x velocity(kgms-1) (kg) (ms-1)

Use this equation to calculate which athlete has the greatest momentum. Mo (A)= 75 kg x 6.5 ms-1 Mo (B) = 80 kg x 5.5 ms-1

= 487.5 kgms-1 = 440 kgms-1 Player A has the greatest momentum.

[B] Angular MomentumConsider the situation of teaching young

children how to swing a softball bat. Is it easier for them to swing using a normal grip or a choke grip? Why?

The choke grip is easier because the COG of the mass is now closer to the axis of rotation (the hands).

Consider an ice skater spinning. How so they speed themselves up in the spin? How do they slow themselves down?

To speed up, they bring their body parts closer to the axis of rotation. Then move them out again to slow down.

Delete the incorrect option in each case.

When the mass is moved closer to the axis of rotation, inertia increases / decreases, and angular velocity increases / decreases. As a consequence the body spins faster.

When the mass is moved further away from the axis of rotation, inertia increases / decreases, and angular velocity increases / decreases. As a consequence the body spins slower.

Other sporting examples of this principle in action include:

1. Pirouettes in ballet2. Somersaults in tumbling3. Springboard diving moves

Plot the change in inertia and angular velocity as the gymnast performs a headstand to forward roll

An

gula

r V

eloc

ity

Iner

tia

High

Low

A B C D E

Key: = INERTIA

= ANGULAR VELOCITY

Explain in biochemical terms the relationship that occurs between moment of inertia and angular velocity as the gymnast performs the headstand to forward roll.As the gymnast tucks A – C, the mass is brought closer to the axis of rotation. AS a consequence inertia decreases and angular velocity (speed of roll) increases. As the gymnast opens out from C - E, the mass is moved further from the axis of rotation. Inertia increases, angular velocity decreases.

Let us assume that the gymnast is unable to stand at the end of performing the skill, instead they fall backwards. Explain in biomechanical detail what may have happened for this to occur.They opened out too early (inertia increases, angular velocity decreases,) i.e. they don’t have enough speed of rotation to get to the standing position.

3.6 Conservation of Momentum

The Law of Conservation of Momentum states:

When objects collide, momentum is conserved throughout.

The total momentum before impact (before the ball is hit) is:

Equal to the momentum of the bat AND the momentum of the ball

Basically:Momentum before impact = momentum

after impact

Using this concept, explain why:a. The white ball in pool slows down

after impacting the black.Some of the momentum of the white ball is passed on to the black ball.

b. When suddenly braking in a car, your body moves forward (thankfully you are wearing a seatbelt).The momentum of the car is transferred to your body. This is why objects in a car are propelled forward on braking.

Remember, the total momentum of the club and ball before impact must equal…

The total momentum of the club and ball AFTER impact

3.7 Generating MomentumForce Summation

[A] Generating Linear Momentum Consider the hockey player. How do

they give maximum momentum to the ball when it is flicked? What are they doing?Get down low, step into the shot, strong grip on lever (stick), use whole body in shot, follow through, good range of motion.

[1] Using body SegmentsWe should look to se as many body segments as possible when trying to give an object maximum momentum. Why?

Because we can maximise the muscular force that each muscle group associated with each segment can generate.

In the hockey illustration, what body segments are being used?

Legs, hip, trunk, shoulder, arms and wrist.

[2] Stretch OutBefore we begin the sequence of movements, such as the throwing action, we should stretch muscles out to their optimal length. Why?It allows the muscle to be contracted with optimum force.

In the hockey illustration, how do we see this principle being applied?Large step forward. Extension of arms around the stick.

[3] Sequencing of Body SegmentsIn effect we use the body like a giant whip. What are the benefits of this?The momentum generated by larger segments is passed onto smaller ones until we male contact/release etc.

In the hockey illustration, how do we see this principle being applied?Legs – trunk – arms – wrist – stick - ball

[4] Timing of Body SegmentsWhat could happen if the timing of body segments is “out of order”?Not only does the movement lack co-ordination but maximum force generated can be lessened.

How does correct timing ensure maximum momentum?It means we use those larger muscle groups first and the smaller muscle groups last.

[5] Full Range of MotionWhat are the benefits of this?The greater the range of motion, the higher the speed of the extremities on release/contact. OR By moving through a greater range of motion we give the lever a longer path through wich to travel, generating more force.

Using your knowledge of generating momentum, explain how the athlete generates maximum momentum to the javelin upon release.

1. They use the large muscle groups of the leg and trunk to generate force initially. This is then passed to the shoulder, arm and finally hand upon release of the javelin.

2. They fully extend the arm (at shoulder) prior to the throwing action.

3. The timing is legs – trunk – shoulder – arm – hand – javelin

4. The arm moves through its full range of motion to maximise lever length and force summation.

[B] Generating Angular MomentumAn eccentric force is…A force applied to one side of the

COGDraw in the position of the force

that needs to be applied in order to generate topspin and backspin on the balls below.

TOP SPIN

FORCE FORCE

BACK SPIN

Draw in the body position of the athlete in order to initiate a dive roll in gymnastics. Explain this position.The COG is in front of the feet (where the force will be applied). This causes a turning force.

How can an athlete generate more angular momentum to the body, or object?Apply greater initial force or move the COG further away from the point of force application.

force

COG

4.2 Factors Affecting Projectile Motion

What is the effect on the projectile of the vertical component?To give it height

What is the effect on the projectile of the horizontal component?To give it distance

The factors affecting the flight path of a projectile are:

1. Gravity2. Air resistance3. Speed of release4. Angle of release5. Height of release6. Spin

[A] GravityWhat is the effect of gravity on a projectile?

It decreases the height the projectile can attain

[B] Air ResistanceDraw the typical flight path of a badminton shuttle.

There are several key factors that bring air resistance into play:1. The larger the surface to volume ratio, the more air resistance

will affect the object, e.g. a badminton shuttle compared to a golf ball.

2. The surface of the object. If the surface is rough then air resistance will be greater.

3. Speed. As speed increases, so does air resistance, e.g. a space shuttle (friction).

4. Mass. The smaller the mass (lighter the object), the more air resistance will affect it.

How can we make sure we still get good distance from our projectile?Have a lower angle of release. Rugby players will kick the ball low.

[C] Speed of ReleaseGenerally the greater the speed of release,

the greater the distance gained

What are the advantages of having a high initial vertical velocity?

It will result in a longer flight caused by more height.What are the advantages of having a high initial horizontal

velocity? It will result in a longer flight time and good distance.

In which sports would a high initial vertical velocity be of advantage?

Gymnastics tumbling, high jump, ski jump (tricks).In which sports would a high initial horizontal velocity be of

advantage? Long jump, ski jump (distance), vaults in gymnastics.

Initial Horizontal velocity

Initial Vertical velocity

Direction of flight

[D] Angle of ReleaseIn sporting situations the angle of release is usually always lower,

around 35˚ to 45˚. Why?Air resistance of the body. The take-off point is usually higher than the landing point, e.g. long jump

What would happen if the angle of release were too high for a given activity?Poor distance gained.

What would happen if the angle of resistance were too low for a given activity?Poor flight time and possibly poor distance.

1. Sports in which distance is important have a lower angle of release 2. Sports in which height or flight time is important have a higher

angle of release

ACTIVITY ANGLE RANK

EXPLANATION

Triple Jump 2 Going for distance

High Jump 4 You need time, but also a little distance to clear bar

Standing Back Somersault

5 You need time to somersault

Javelin Throw 3 You need distance, but also flight time

Racing Dive in Swimming

1 You dive down

[E] Height of ReleaseWhy might this be?

Time in the air will be greater.Would this mean that a golfer hitting a ball off

the top of a hill would hit it further than a golfer at the bottom of the hill? Why?YES – the ball will stay in the air longer so will have a greater chance to fly further. This assumes the same club and force is used.

In what other sports is application of this principle important?Javelin. Hold the javelin up high to gain a greater height of release.

The reason behind this can be summarised as follows:

1. As the height of release increases, the angle of release decreases.

2. As the height of release decreases, the angle of release increases.

[F] SpinWhat happens to the distance achieved with a topspin

shot compared to one with backspin?A topspin shot gives poorer distance compared to backspin.

1. Range is decreased with topspin 2. Range is increased with backspinWhat will happen with a backspin shot?

A region of high pressure (H) is created under the ball and low pressure (L) above the ball. Air moves from H-L. As a consequence the ball tends to ‘stay up’ longer.

Draw this on the two balls below:TOPSPIN BACKSPIN

L H

DIRECTION OF BALL

DIRECTION OF BALL

H L

6.2 Phases of Execution

Most complex skills can be broken down into three phases of execution:

1. Preparation phase2. Execution phase3. Post action/follow through phrase

Label each diagram accordingly.(From left to right) 1,2,3

How would you describe the key features of each phase? What is its purpose?

Phase 1: This is where the athlete sets themselves up to execute the skill. Mental preparation. Addressing the hockey ball (as in example above)

Phase 2: This is the force producing movements required to perform skill. In this phase the principles of force summation, timing etc are used.

Phase 3: This allows forces to be controlled or dissipate to prevent loss of control or injury.

The greater the force that can be applied to the ball, the greater the acceleration of the ball.By using correct force summation (timing, sequencing, body segments, stretch and range of motion), large forces can be generated that will be passed on to the ball.

Acceleration & Force

(2nd Law)

The muscles have to work hard now to decrease the forces generated during preparation and execution to maintain control. The greater the forces that were generated, the greater the forces required to slow down and control the movement in the follow through.

Body is positioned ready to overcome the inertia of the ball and change its direction.Body is being prepared to move.Greater forces will be required to overcome the inertia of the body compared to the ball because the player weighs more.

Inertia (1st

Law)

Newton’s Laws of Motion

Follow-through

Execution Phase

Preparation Phase

To be consider

ed

Key biomechanical principle

The sequence and timing of body segments is legs then hips then trunk then shoulders then arms and finally hands.The stick head will move quickly through the range of motion generating large forces on contact with ball.The extension of the arms and stepping forward means muscles will be at optimum force.This also allows for the greatest possible range of motion allowing for greater force to be generated.

The player may be going through the movements in their head to make sure the correct body part adds the movement at the correct time.Body is positioned to increase the chances of this happening.

Body segments Stretchin

g outSequenci

ng of segmentsTiming

Range of motion

The ball will travel in the direction that the force is applied, Therefore, if the stick follow through is toward s they target, that is the direction the ball will travel in.

For every action there is an equal and opposite reaction. If a lot of force is given to the ball it will react and travel a good distance.The ball will travel in the direction that the force is applied.

Action &

Reaction

(3rd Law)

Newton’s Laws of Motion

Generating

Momentum

(Force Summatio

n)

Follow-throughExecution PhasePreparation Phase

To be considered

Key biomechanical principle

The rear leg stays back as the stick travels in front of the body because, as one part of a body moves away from the centre of gravity, another body part must move in the opposite direction to ensure balance is maintained.

The large step towards the target increases the size of the abase of support meaning that as the player executes the shot, their centre of gravity remains within the base of support, keeping them stable and balanced throughout.

The stable body position ensures the body is balanced and controlled before executing the shot. The centre of gravity (COG) lies within the margins of the base of support (BOS)

Centre of gravity

Base of support

Line of gravity motion

The follow through is designed to reduce the momentum in the system so the player remains stable and ready to move on to the next skill.

As they move through the execution phase, momentum generated by the legs and hips moves to the trunk, then shoulder, arms and finally to the stick.Following contact, some of the momentum is transferred to the ball and it begins its flight path.Momentum is conserved throughout the movement (ball and body)

The player positions the body such that momentum can be transferred through the body to the ball.By ensuring correct sequencing and timing of body segments, they will enhance the transfer of momentum

Transfer &

Conservation of

momentum

Stability & Balance

Follow-throughExecution PhasePreparation Phase

To be considered

Key biomechanical principle

The follow through will help determine the final path. Of the player ‘hooks; the stick, the shot too will be hooked.

With force summation, the ball will be given a certain amount of speed upon release. The greater the force given to it, the greater the speed of release.

If the player drops the right shoulder and lowers their body behind the ball, it will be given more height rather than distance at take-off (increased angle)

The player positions the stick on the bottom half of the ball in order to get ‘under’ it.The angle at which the stick contacts the ball will help determine the angle of release and therefore how high and how far it will go.

Speed of release

Height of release

Angle of release

Spin

Projectile Motion

Follow-throughExecution PhasePreparation Phase

To be considered

Key biomechanical principle