Measurement Of Forces: Lecture Ii

Front 1

Force

Back 1

a push or pull that tends to cause motion

Front 2

Newton's Laws of Motion

Back 2

I - every object in a state of motion tends to stay in motion
II - F=ma
III - every action has an equal and opposite reaction

Front 3

Inertia
Mass
Weight

Back 3

I - resistance to movement
M - amount of matter in body
W - gravitational pull on body

Front 4

Main Determinant of Force

Back 4

F=ma
mass and acceleration

Front 5

How do we measure forces?

Back 5

measured using force plates = anterior/posterior and medial/lateral directions for vertical forces

Front 6

Newton's 3rd Law Applied to Gait

Back 6

III - every action has an equal and opposite reaction
Force placed into ground causes an equal and opposite reaction through the skeleton

Front 7

Ground Reaction Force

Back 7

how much force you are placing in the ground that is being transmitted back up through your spinous processes

Front 8

Ground Reaction Force Distributions During Gait

Back 8

Changing continuously during gait: heel contact, mid-stance, and pre-swing

Front 9

Piezoelectric Effect

Back 9

Measured through force plates - crystals are compressed/stressed/loaded and electricity is produced

Front 10

Pressure

Back 10

Measured by force plates:
P=F/A
Measured in N/m2 and lb/in2

Front 11

Definition of Center of Pressure

Back 11

pressure on the base of support where the pressure would be centered over one point - strike index

Front 12

Types of Strike Index

Back 12

rear foot striker
mid-foot striker
forefoot striker

Front 13

COP and Postural Stability: How does it vary throughout gait?

Back 13

It is a single measure
Oscillates throughout gait as you sway back and forth - more focused in the forefoot strike index

Front 14

Factors Measuring Sway

Back 14

range
mean
SD
COV

Front 15

Less sway doesn't mean _______ stability.

Back 15

more

Front 16

More coordination = _______ stability.

Back 16

more

Front 17

Definition of Center of Mass

Back 17

point equivalent to the total body mass in the global reference system: varies in relation to shape/orientation of object

Front 18

Factors that Affect COG/COM

Back 18

base of support
amount of mass
location of mass
- position of body segments and height of COM above base
- Added external mass

Front 19

Purpose of Balance Method

Back 19

used to determine COM

Front 20

How does COM cause you to fall?

Back 20

COG/COM can fall outside of based of support = fall

Front 21

What happens if you fall outside your base of support?

Back 21

corrective stumble

Front 22

Center of Gravity During Gait

Back 22

when one foot is on the ground and the other is in swing - your body falls out of its base of support - you are continually falling and catching yourself throughout the gait cycle

Front 23

Changes in COM & GRF When Walking at Different Speeds

Back 23

COM is higher with increasing speed
GRF is higher with increasing speed

Front 24

Postural Control of COP in Relation to Anterior & Lateral Sway

Back 24

Anterior - increase in anterior sway, increase in plantarflexor activity
Lateral - increase in lateral sway, increase in hip abductor/adductor activity

Front 25

COP Excursion

Back 25

located within base of support and can be achieved by regulating joint and muscle stiffness:
- intrinsic muscle stiffness that dependent on the viscoelastic properties
- neural component

Front 26

Static Posturography

Back 26

subjects stand quietly on a face plate which records COP excursions
- used in PD patients
- increase in displacement = increase in instability

Front 27

Dynamic Posturography

Back 27

subjects stand quietly on a movable support surface that suddenly rotates up and displaces the subject backwards
- Gastrocs are activated
- increase in COG displacement in PD pts
- increase in latency in PD pts

Front 28

Feedforward and Feedback Mechanisms

Back 28

Feedforward: anticipated postural instability
Feedback: unanticipated postural instability

Front 29

Feedforward Control

Back 29

Triggered centrally before voluntary movement
- around 100 msec
- faster than voluntary rxn time

Front 30

Muscles Activated by Backward and Forward Sway

Back 30

B - Abductors, Quads, Tibs
F - Para, Hams, Gastrocs

Front 31

Postural Threat

Back 31

Hydraulic platform lift used to manipulated the height which is set at 3 different levels:
- Low: 40 cm
- Med: 100 cm
- High: 160 cm

Front 32

Overall Effect of Amplitued & Frequency in Relation to Postural Threat

Back 32

As postural threat increases:
- decrease in amplitude of COP
- increase in frequency of COP

Front 33

LOG During Quiet Stance

Back 33

it falls between the knee and hip joint:
- passive tension around ankle joints oppose external forces with no force around knee and hips
- LOG falls anterior to foot causing DF

Front 34

COM Falls anterior to Ankle Causes:

Back 34

tendency to fall unless opposed by Soleus activity
if Soleus activity is not enough - then Gastrocs is activated

Front 35

Motion at Joints: Ankle and Hip

Back 35

- Ankle used in during quiet stance and when small pertubations applied to body
- dorsiflexors and plantarflexors help control the mechanism

Front 36

Hip Strategy is used for:

Back 36

used for anterior/posterior control if pertubations are too large for ankle strategy to support it

Front 37

Hip Strategy Occurs as a Consequence of:

Back 37

1. increased postrual sway
2. larger pertubations to body
3. inability to control motion at the ankle joint
4. perceived instabilities due to threat to postrure

Front 38

Control of Medial/Lateral Sway

Back 38

controlled by hip abductors/adductors - loading of one limb and unloading of the opposite limb (load/unload mechanism)

Front 39

Muscles used for:
- anterior/posterior
- medial/lateral

Back 39

AP - ankle muscles
ML - adductors/abductors
Both activated at the same time