why we walk the way we do (ug)
TRANSCRIPT
Most of the material in this lecture is available on my blog site www.wwRichard.net
The interactive tools I use in this lecture cannot easily be embedded in this presentation. Instead use the drop down menus on the blogsie to go to “Verne”. (Note that these are written with Flash so will not work on Apple products such as i-pads and i-phones.)
Go to “videos” to see a series of screencasts that cover the same material as my lecture. They are entitled “Why we walk the way we do” and the most relevant material is from screencast 4 onwards.
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Why we walk the way we do
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Richard BakerProfessor of Clinical Gait Analysis
www.wwRichard.net , http://www.youtube.com/user/WalkingWithRichard
Introduction
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4
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-15°
0°
15°
30°
45°
60°
75°
-20 0 20 40 60 80 100 120
Kn
ee f
lexi
on
(d
egr
ees)
% gait cycle
Knee
Left
Right
1DS 2DSESS MSS LSS ESw MSw LSw
Challenge
• Can I describe the shape of the gait
graphs in a way that all of you can
understand?
• Start off with simple pattern.
• Introduce small steps that we understand
• End up with full gait pattern.
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Warning
• I’ve prepared this material primarily
because I don’t know of any text book that
describes walking easily and rigorously.
• Several popular theories are simply wrong
(e.g. Determinants of Gait).
• Some of it will be different to what many
practicing physiotherapists understand.
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Based on ideas from:
Verne Inman
Howard Eberhart
Jacqueline Perry
David Winter
James Gage (Prerequisites of normal walking)
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Attributes of walking
Energy conservation
Clearance in swing
Appropriate step length
Support of bodyweight
Smooth transitions
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Attributes of walking
Energy conservation
Clearance in swing
Appropriate step length
Support of bodyweight
Smooth transitions
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Walking is amazingly efficient
Walking for a kilometre at comfortable speed
(4km/h) uses up the energy in two
teaspoons of sugar.
A healthy child has to walk for over an hour
to work off the energy contained in a can of
coke.
You could walk for 154km on the equivalent
of 1 litre of petrol (3 x as far as Toyota Prius)
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Simple Pendulum1
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-2.5
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2.5
5.0
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-10
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0
5
10
15
0.0 1.0 2.0
Ener
gy (
J)
Time (sec)
Total energy
Kinetic energy
Ho
rizo
nta
l vel
oci
ty (
m/s
)
Horizontal velocity
Potential energy
• Mass below pivot
• Conserves energy
• Periodic oscillation
• Natural frequency
• Doesn’t go anywhere
Inverted Pendulum1
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• Mass above pivot
• Conserves energy
• No oscillation
• Moves forward
0.0
0.5
1.0
1.5
2.0
0
50
100
150
0.0 0.1 0.2 0.3 0.4 0.5
Ho
rizo
nta
l vel
oci
ty (
m/s
)
Ener
gy (
J)
Time (sec)
Total energy
Kinetic energy
Horizontal velocity
Potential energy
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Fierljeppen 15.55m
http://www.youtube.com/watch?feature=endscreen&NR=1&v=QeMAMv6GaJQ
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60
0
70
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75
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30
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Compass gaita
b
c d
Hip flexion
Pelvic tilt
Knee flexion
Dorsiflexion
Foot angle
e
a) No double support so stance and swing both 50% of gait cycle.
b) Pelvis tilt fixed at 14° (because PSIS above ASIS)
c) Hip extends throughout stance
d) Hip flexes throughout swing
e) Femur movements offset from zero because of pelvic tilt.
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60
0
70
-20
75
-15
30
-30
-30
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Compass gaita
b
c d
f
g
h
Hip flexion
Pelvic tilt
Knee flexion
Dorsiflexion
Foot angle
e
f) No knee movement
g) Ankles mirror hips exactly
h) Feet are horizontal as they scrape along floor.
Energy conservation2
3
0.0
0.5
1.0
1.5
2.0
0
50
100
150
0.0 0.1 0.2 0.3 0.4 0.5
Ho
rizo
nta
l vel
oci
ty (
m/s
)
Ener
gy (
J)
Time (sec)
Total energy
Kinetic energy
Horizontal velocity
Potential energy
The energy that has been preserved through
one step must be passed on to the next step
as kinetic energy
Clinical implications
• Walking is a dynamic activity requiring
preservation of kinetic energy from step to
step.
• It can’t be taught (re-taught) as a
sequence of static postures.
• Cadence and step length (and hence
speed) are all determined by quality of hip
movement.
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Energy conservation
Clearance in swing
Appropriate step length
Support of bodyweight
Smooth transitions
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Clearance2
6
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60
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75
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Clearancei) Minimum toe clearance occurs about half way
through swing
j) Knee flexes to at least 50° by mid swing
k) Hip must be flexed early in swing
l) Ankle must be at least neutral
m) Foot will follow knee (moderated by hip flexion)
l
Hip flexion
Pelvic tilt
Knee flexion
Dorsiflexion
Foot angle
i
j
k
m
Clinical implications
• Plantarflexion and mild amounts of knee
flexion both make clearance difficult.
• You need a lot of knee flexion for it to be
useful for clearance.
• People who have difficulty with clearance
can “vault” to make the other leg longe
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Clearance2
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Energy conservation
Clearance in swing
Appropriate step length
Support of bodyweight
Smooth transitions
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Step length3
1
Adequate step length
A 10° change in joint angle will increase step
length by:
Femur-femur angle +21%
Leading knee flexion -13%
Trailing knee flexion +13%
Trailing heel rise +5%
Pelvic rotation +5%
Trailing dorsiflexion 0%
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60
0
70
-20
75
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30
-30
-30
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Step lengthn) Step length primarily determined by difference
in hip flexion-extension between opposite foot contact and foot contact.
o) Require good knee extension at foot contact.
p) Require some knee flexion before opposite foot off.
Hip flexion
Pelvic tilt
Knee flexion
Dorsiflexion
Foot angle
n
p
o
Clinical implications
• Step length is driven by hip movement.
• Obtaining hip extension on the trailing leg
is just as important as obtaining hip flexion
on the leading leg.
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Energy conservation
Clearance in swing
Appropriate step length
Support of bodyweight
Smooth transitions
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Upward velocity
• Upward velocity reduces throughout
• There is a downward acceleration
• Downward forces are bigger than upwards forces
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Bodyweight
Energy conservation
Clearance in swing
Appropriate step length
Support of bodyweight
Smooth transitions
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40
41
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60
0
70
-20
75
-15
30
-30
-30
30
Support of Bodyweight
Hip flexion
Pelvic tilt
Knee flexion
Dorsiflexion
Foot angle
The inverted pendulum motion requires a double support phase.
r. Stance must thus be longer than swing.
s. Opposite foot contact and opposite foot off become meaningful.
Energy conservation
Clearance in swing
Appropriate step length
Support of bodyweight
Smooth transitions
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Two transitions
1. Stance to swing at foot off
2. Swing to stance at foot contact
“It’s a lot easier to fall off a log than onto one”Richard Baker – August 2009
The swing to stance transition is by far the
more difficult
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Heel strike
Foot strike
Foot contact
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David Winter
“The trajectory velocity of the heel
immediately prior to [foot contact] is virtually
zero vertically and low in the horizontal
direction; such findings raise the question as
to why many researchers refer to this initial
contact as "heel-strike."
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Winter, D. A. (1992). Foot trajectory in human gait: a precise and multifactorial motor control task. Phys Ther, 72(1), 45-53; discussion 54-46.
David Winter
“Primary tasks of walking:
3) control of the foot trajectory to achieve
safe ground clearance and a gentle heel
or toe landing."
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Winter DA. Biomechanics and motor control of human movement.Third Edition, John Wiley and Sons, Hoboken, New Jersey, 2004
Smooth Transitions –
Foot
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Smooth transition - Foot4
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Heel speed is less than 5% of maximum at foot contact
Horizontal- late swing5
0
Horizontal – late swing
Achieved through swing limb mechanisms:
1. Knee flexion before foot contact
2. Plantarflexion before foot contact
You don’t read this in the text books!
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Horizontal- early stance5
2
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60
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Smooth transitions - Foot
t) Knee flexes before initial contact and continues into early stance.
u) Ankle has to be approximately neutral and plantarflexing prior to foot contact and this continues in early stance.
v) Foot angle is modified by changes in knee and ankle in early stance and comes down to horizontal in early stance.
Hip flexion
Pelvic tilt
Knee flexion
Dorsiflexion
Foot angle
t
u
v
Smooth Transitions –
Centre of Mass
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Smooth transitions – Centre of mass5
5
Centre of Mass moving at maximum speed
1.5 m/s.
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40%Start of late stance/swing
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40%Start of late stance/swing
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50%Left foot contact
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60%Right foot off
Trailing limb must get longer during late
stance and 2nd double support
1. Plantarflexion resulting in heel rise
2. Control knee flexion (reduces leg length)
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Smooth transitions – Centre of mass
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50%Left foot contact
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60%Right foot off
Leading limb must get shorter during 1st
double support
1. Stance phase knee flexion
2. Some contribution from ankle
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Smooth transitions – Centre of mass
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60
0
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75
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30
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Smooth transitions -
vertical
w. Heel rise through double support
x. Driven by plantarflexion through double support
Hip flexion
Pelvic tilt
Knee flexion
Dorsiflexion
Foot angle
w
x
Clinical implications
• Most of us avoid shock rather than
absorbing it.
• Achieving smooth transition from swing to
stance requires a number of co-ordinated
mechanisms. It is no wonder that people
with disabilities find this so difficult
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Summary
• We have succeeded in explaining all the
significant features of the sagittal plane
gait pattern in terms of five attributes of
walking.
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Coronal plane
• Not going to start again!
• Not very much happens in the coronal plane during healthy walking other than small movements at the pelvis and a mild movement of the centre of mass from side to side.
• The importance of both of these is greatly exaggerated in the literature and by clinicians
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Energy conservation
Clearance in swing
Appropriate step length
Support of bodyweight
Smooth transitions
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Attributes of walking
Thanks for listening
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