Transcript biomechanics2008

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 Gravity
The 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 dance
Twist in diving
Spinning in ice-skating
Transverse
Forward/backward somersault
Forward/backward roll
Sagittal
Cartwheel
Cricket delivery
Barani or free cartwheel
1.4 Levers
A lever consists of three parts
1. Resistance
2. Effort
3. 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 saw
Crowbar
Hammer pulling
out a nail
Second
The resistance lies
between the
fulcrum and the
point of effort
Wheelbarrow
Opening a door
by the handle
Rowing a boat
Third
The effort lies
between the
resistance and
the fulcrum
Biceps curl
Most 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
Skip pages 123 -130
Biomechanics
Section 2: Motion
3.2 Newton’s Laws of Motion
[A] Law 1
An object at rest tends to remain at rest unless acted upon by some
external force
This 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 2
If 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 acceleration
B. 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 3
When we apply a force to something it is known as action force
The object we apply a force to, applies a force back, a reaction force
Reaction
Action
Reaction
Action
Action
Reaction
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.
Skip pages 133-136
3.5 Momentum
We 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 Momentum
Momentum 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 Momentum
Consider 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.
When the mass is moved closer to the
When the mass is moved further away
Delete
the incorrect
option
case.
axis of rotation,
inertia increases
/ in each
from
the axis of rotation, inertia
decreases, and angular velocity increases
increases / decreases, and angular
/ decreases. As a consequence the body
velocity increases / decreases. As a
consequence the body spins slower.
spins faster.
Other sporting examples of this principle in
action include:
1. Pirouettes in ballet
2. Somersaults in tumbling
3. Springboard diving moves
Plot the change in inertia and angular velocity as the
gymnast performs a headstand to forward roll
High
Key:
= INERTIA
Angular
Velocity
= ANGULAR
VELOCITY
Inertia
Low
A
B
C
D
E
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 Momentum
Force 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 Segments
We 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 Out
Before 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 Segments
In 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 Segments
What 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 Motion
What 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 Momentum
An eccentric force is…
A force applied to one side of the COG
Draw 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.
COG
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.
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. Gravity
2. Air resistance
3. Speed of release
4. Angle of release
5. Height of release
6. Spin
[A] Gravity
What is the effect of gravity on a projectile?
It decreases the height the projectile can attain
[B] Air Resistance
Draw 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 Release
Generally the greater the speed of release,
Initial
Vertical
velocity
the greater the distance gained
Direction of flight
Initial
Horizontal
velocity
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.
[D] Angle of Release
In 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.
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
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
[E] Height of Release
Why 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] Spin
What 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 backspin
What 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
H
DIRECTION
OF BALL
BACKSPIN
L
DIRECTION
OF BALL
L
H
6.2 Phases of Execution
Most complex skills can be broken down into three phases of execution:
1. Preparation phase
2. Execution phase
3. 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.
Key
biomechanical
principle
To be
considered
Inertia
(1st Law)
Newton’s
Laws of
Motion
Acceleration
& Force
(2nd Law)
Preparation Phase
Execution Phase
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.
Follow-through
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.
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.
Key biomechanical
principle
Newton’s
Laws of
Motion
Generating
Momentum
(Force
Summation)
To be considered
Preparation Phase
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)
Body
segments
Stretching
out
Sequencing
of
segments
Timing
Range of
motion
Execution Phase
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.
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.
Follow-through
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.
Key biomechanical
principle
To be considered
Transfer &
Conservation
of
momentum
Centre of
gravity
Stability &
Balance
Base of
support
Line of
gravity
motion
Preparation Phase
Execution Phase
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
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 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)
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.
Follow-through
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.
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.
Key biomechanical
principle
Projectile
Motion
To be considered
Speed of
release
Height of
release
Angle of
release
Spin
Preparation Phase
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.
Execution Phase
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)
Follow-through
The follow through
will help determine
the final path. Of
the player ‘hooks;
the stick, the shot
too will be hooked.