wk 6- kinetics and joint movements

Question 1

Define the study of kinetics

Answer 1

study of forces, moments, masses and accelerations, but without looking at position or orientation of the objects involved (kinematics)

Question 2

first, second and third newtons law

Answer 2

1. velocity of a body remains constant unless the body is acted upon by an external force
2. the acceleration of a body is parallel and directly proportional to the net force and inversley proportional to mass
3. the mutual forces of action and reaction between two bodies are equal, opposite and colinear

Question 3

force platform does what

Answer 3

gives total force applied by the foot to the ground, does not show the distribution of different parts of this force on the walking surface

Question 4

what does force plate measure

Answer 4

the electrical output signals produce
1. 3 componens of force vetocr, (vertical, lateral and fore aft)
2. two coordinates of the centre of pressure
3. moments about the vertical axis

Question 5

why does ground reaction force magnitude increase/decrease during the gait cycle

Question 6

why is it important to consider the direction (not just magnitude) of GRF vectors?

Question 7

Discuss the magnitude and direction of ground reaction force vectors with respect to key events and periods in the gait cycle

Answer 7

during walking gait, the centre of mass rises during single support and falls during double support

since force = mass x acceleration, acceleration of centre of mass has an impact on the magnitude of forces exerted on the foot

Question 8

why does vertical GRF look like an M

Answer 8

result of an upward acceleration of the centre f gravity during early stance, a reduction in downward force as the body flies over the leg in mid stance and a secon peak due to the deceleration as the downward motion is checked in late stance

Question 9

vertical GRF during the gait periods IC, early stance, mid stance, late stance and terminal

Answer 9

A. At IC, force quickly rises as ipsilateral limb
accepts weight from contralateral limb
B. Forces rise above RESTING body weight during
early stance
C. Force falls below resting body weight during
midstance
D. Body weight rises above RESTING body weight
in late stance
E. During terminal double support, weight quickly
drops as body weight is transferred to the
contralateral limb

Question 10

area under the curve

Answer 10

force time integral, force over time

Question 11

Describe the clinical importance of moment data in gait analysis

Question 12

Discuss internal and external joint moments with respect to key events and periods in the gait cycle

Question 13

initial contact GRF- direction and magnitude

Answer 13

changes from upwards to upwards and back

Question 14

loading response

Answer 14

increases rapidly in magnitude, its direction being upwards and backwards

Question 15

opposite toe off

Answer 15

increase in vertical GRF magnotude, as now weight is being taken full on the stance limb

Question 16

mid stance

Answer 16

Centre of pressure forward along the foot from foot flat onwards, moving into forefoot prior to heel rise

Question 17

heel rise

Answer 17

cente of pressure forward due to ankle plantarflexion. now at forefoot and vector passes in front of knee joint

Question 18

opposite initial contact

Answer 18

second peak of GRF, just prior to opposite initial contact

Question 19

toe off

Answer 19

knee and hip flexion aided by backward position of vector. magnitude of the grf declines, alling to zero as the foot leaves the ground

Question 20

GRF vector throughout gait

Answer 20

butterfly curve looking

Question 21

moment is

Answer 21

A moment of force is multiplying magnitude of force by its perpendicular
distance from the fulcrum or pivot point
* Also referred to as “torque” or “turning moment

Question 22

moment of force is generated around joints by 3

Answer 22

1. ground reaction forces
2. muscle activity
3. tension of soft tissues (ligaments)

Question 23

moment =

Answer 23

force x distance

Question 24

types of joint moments

Answer 24

internal
1. active - muscle contraction
2. passive - tension of ligaments

external
-due to gravitational forces (GRF)

Question 25

initial contact joint moments at the hip, knee and ankle

Answer 25

hip
internal extensor joint moment from contraction of hip extensors (external flexion moment -GRF)

knee
internal flexor moment, from contracture of hamstrings
external extensor moment (GRF)
then becomes external flexor moment once knee flexion has occurred

ankle
internal dorsiflexor moment from eccentric contraction of dorsiflexors
small external plantar flexor moment (GRF)

Question 26

midstance joint moments at the hip, knee, ankle

Answer 26

hip
internal extensor moment dissipates and is replaced by an internal flexor moment
external moment moves from flexion to extension

knee
internal extensor moment- quads contract
force vector remains behind the joint causing external flexor moment
becomes external extensor moment due to forward progression of centre of mass (quads turn off)

ankle
increasing internal plantarflexion moment as the GRF vector moves from forefoot
external dorsiflexion moment (GRF)

Question 27

terminal stance joint moments at the hip, knee, ankle

Answer 27

hip
peak hip internal flexor moment around opposite intital contact
decreasing external extension moment

knee
flexion of the knee in terminal stance leaves the knee joint in front of the force vector and changing the internal moment from flexor to extensor
therefore external moment is extension which changes to flexion just before contralateral initial contact

ankle
large internal plantar flexor moment created by a concentric contraction
force vector is anterior to ankle, creating large external dorsiflexor moment