Ch 14

Question 1

Center of gravity

Answer 1

The balance point of the body
- linear force sum to zero
- torques sum to zero
The point which a body would balance without a tendency to rotate

Question 2

Line of gravity

Answer 2

Imaginary line outside of the body that is in line with the COG

Question 3

Center of pressure

Answer 3

Point at which the vector for ground reaction force is applied
Ex: quiet standing- COP is almost directly over COG
Ex: postural sway- when standing as we sway the COP moves along with the foot placement taking the force

Question 4

Equilibrium

Ex:

Answer 4

Object at rest, balanced forces
Sum of forces and torques equals zero
Ex: balancing a pencil on your finger

Question 5

Stability

Answer 5

After slight alteration in objects position it returns to original position
Ex: someone pushing you and you being able to return to normal position

Question 6

Are all objects in equilibrium also stable?

Answer 6

No, standing on one leg we are not able to maintain balance after a heavy push

Question 7

Three types of Equilibrium

Answer 7

Stable Eq
Unstable Eq
Neutral Eq

Question 8

Stable Equilibrium

Ex and human ex

Answer 8

Disturbing the object raises its COG
Ex: lifting a box up on one side just Highers it’s COG
Human ex: raises our COG in the air through a yoga mvmt

Question 9

Unstable Equilibrium

Ex and human ex

Answer 9

Disturbing the object lowers its COG
Ex: triangle pushed down lowers its COG and will not be stable
Human ex: handstand

Question 10

Neutral Equilibrium

Ex and human ex

Answer 10

Disturbing the object doesn’t change the COG
Ex: ball rolling it’s moving but the COG is not going to change
Human ex: laying flat

Question 11

Three factors that affect stability

Answer 11

1. ) size of the base of support
2. ) relation of the line of gravity to the base of support
3. ) height of the center of gravity

Question 12

1.) size of the base of support

Answer 12

COG must remain within base of support in order to maintain equilibrium
- easier to do with larger base of support

Question 13

How does shape of base of support helps to resist forces? Explain.

Answer 13

-One foot forward one foot back prepares for anterior or posterior forces
Ex: car coming to hit you or you’re about to be tackled

• wiser lateral stance prepares for lateral forces
  Ex: someone pushing you from the side

Question 14

2.) Line of gravity in relation to base of support

Answer 14

LOG has to be in line with base of support

- if this isn’t met stability and equilibrium is not possible

Question 15

3.) height of the center of gravity

Answer 15

Lower COG most stable, higher COG much harder to stabilize compared to a low COG

Question 16

Other factors affecting stability

Answer 16

Body’s inertia (mass) 
Friction of the ground
Segmental alignment
Physiological factors 
- vision 
- proprioception 
- vestibular system

Question 17

Mass and moment of inertia

Answer 17

Greater inertia and mass more stability

- the amount of force needed to effect a change in motion is proportional to the inertia

Question 18

Friction

Answer 18

Inadequate friction makes it harder to maintain stability

Question 19

Segmental alignment

Answer 19

When segments are all aligned it’s easy to be stability but when a segment is out of line another segment has to be used to stabilize it making overall stability harder

Question 20

Physiological factors

Answer 20

Vision
Proprioception
Vestibular

Question 21

Mobility

Answer 21

Mvmt of an object

Question 22

Inverse relationship of mobility and stability

Examples?

Answer 22

More mobile less stable
Ex: running or changing direction in football
More stable less mobile
Ex: standing or sitting in place

Question 23

Mobility quick start

Answer 23

Line of gravity close to the edge of the base of support

Ex: track runner on the blocks

Question 24

Mobility quick stop

Answer 24

Move line of gravity away from edge of base of support

Ex: baseball pitch stopping himself after the throw

Question 25

Posture

Answer 25

Shape or configuration of the body

Question 26

Static posture

Answer 26

During quiet sitting or standing

Question 27

Dynamic posture

Answer 27

During movement

Question 28

Postural sway in static posture and what is it an indicator of?

Answer 28

Slight pendulum like motion of the body | - it can help to be an indicator of stability within a person

Question 29

Postural sway Sagittal plane Frontal plane

Answer 29

Sagittal- 2-3cm | Frontal- 1-2cm

Question 30

Conditions associated with increased postural sway (5)

Answer 30

``` Closing eyes Raising hand above head One legged stance (compared to two) Increased age Neurological impairments - Parkinson’s - bipolar disorder ```

Question 31

Three postural adaptations

Answer 31

- Ankle strategy- relying on ankles to maintain or regain stability - hip strategy- bending over we use our hips to remain stable and hold it - Stepping strategy- line of gravity goes away from base of support to move forward

Question 32

Explain how a body would make postural adaptations during a bus ride?

Answer 32

- Foot placement towards the direction the bus is moving - leaning toward the turn the car is making to fight the centrifugal force - core activation to keep body more stable

Question 33

Newtons law of reaction in relation to dynamic posture

Answer 33

When one body’s segments flow through the kinetic chain other parts will have to follow along with it

Question 34

What is key for dynamic posture?

Answer 34

The relationship between center of gravity, center of pressure, and momentum

Question 35

Two types of postural adjustments what are they and give a definition and example.

Answer 35

- Anticipatory (feed forward) Ex: preparing to lift a heavy box, something you’re about to lift in the gym - proprioceptive (feedback): make corrections to ensure the stability is achieved at the end of the mvmt Ex: squatting down you need to focus on maintaining proper posture to not hurt your back

Question 36

Role of instability in strength training

Answer 36

- will train the smaller more postural focused muscles - could also cause pain because movement is difficult and primary movers are no longer activated from insufficient movement