Biomechanics of Walking
D. Gordon E. Robertson, PhD, FCSB
Biomechanics, Laboratory,
School of Human Kinetics,
University of Ottawa, Ottawa, Canada
Quantitative Domains
• Temporal
– phases (stance/swing) and events (footstrike, toe-off), stride rate
• Electromyography
– muscle activation patterns
• Kinematic (motion description)
– stride length, velocity, ranges of motion,
acceleration
• Kinetic (causes of motion)
– ground reaction forces, pressure patterns,
joint forces, moments of force, work, energy
and power
Temporal Analysis
•
•
•
•
Stride time (s)
Stride rate = 1/time (/s)
Stride cadence = 120 x rate (b/min)
Instrumentation
– Photocells and timers
– Videography (1 frame =
1/30 second)
– Metronome
Donovan Bailey sets
world record (9.835)
despite slowest
reaction time (0.174)
of finalists
Electromyography
Bortec system
Delsys electrodes
Noraxon system
Mega system
EMG of normal walking
rectus femoris
vastus lateralis
gait
initiation
strides
tibialis anterior
gastrocnemius
biceps femoris
heel switch
EMG of normal walking
rectus femoris
vastus lateralis
rectus femoris
contracts twice per
cycle, oncetibialis
in earlyanterior
stance and once in
late stance
gastrocnemius
biceps femoris
heel switch
EMG of normal walking
rectus femoris
vastus lateralis
biceps femoris has one
longer contraction in
late swing and early
stance, synchronous
with one burst of
rectus femoris
tibialis anterior
gastrocnemius
biceps femoris
heel switch
EMG of normal walking
tibialis anterior has
two bursts of activity
one in mid-swing
and one during early
stance. It is very
active at initiation.
rectus femoris
vastus lateralis
tibialis anterior
gastrocnemius
biceps femoris
heel switch
EMG of normal walking
gastrocnemius has one
long contraction
throughout stance.
rectus femoris
It is asynchronous
with tibialis anterior.
vastus lateralis
tibialis anterior
gastrocnemius
biceps femoris
heel switch
Kinematic Analysis
• Linear position
3D digitizer
– Ruler, tape measure, optical,
potentiometric
• Linear velocity
– radar gun, photo-optical timer
• Linear acceleration
– Accelerometry, videography
miniature
accelerometers
radar gun
Gait Characteristics Walking
a
walking
step width
stride length
b
stance phase,
left foot
swing phase,
left foot
step length
one gait cycle
left foot
right foot
double-support
left foot-strike
right toe-off
left toe-off
right foot-strike
single-support
time
Gait Characteristics –
Running/Sprinting
a
running/sprinting
stride length
b
stance phase,
left foot
swing phase,
left foot
step length
one gait cycle
left foot
right foot
flight phase
right foot-strike
left foot-strike
right toe-off
left toe-off
time
Motion Capture
• Cinefilm, video or
infrared video
• Subject is filmed and
locations of joint
centres are digitized
Basler charge-coupled
device (CCD) camera
Panasonic
videocamera
Vicon
infra-red
camera
Video
data
Video Motion Capture
(e.g., SIMI or APAS)
EMG data
Force platform
data
F-Scan
data
3D motion
data
Passive Infrared
Motion Capture
(e.g., M.A.C.)
Infrared
video
cameras
M.A.C.
system
Kistler force platforms
Active Infrared
Motion Capture
• NDI’s Optotrak
Infrared
Infrared
video
emitting
cameras
diodes
Computerized Digitizing
(Vicon, SIMI, etc.)
Gait and Movement
Analysis Lab (e.g., Vicon)
• Vicon Nexus or
Workstation
• Vicon MX cameras
• Kistler and AMTI
force platforms
• Bortec EMGs ( 8channels) or Delsys
Trigo (16 EMGs + 24
accelerometers)
• Tekscan or Pedar inshoe pressure
mapping systems
Full-body 3D Marker Set
3D Geometric Model
(Visual3D)
from markers to
joint centres and
stick-figure of
body
from stick-figures to
geometrical solids
of revolution with
known inertial
properties
Kinetic Analysis
Causes of motion
• Forces and moments of force
• Work, energy and power
• Impulse and momentum
• Inverse Dynamics derives forces and
moments from kinematics and body
segment parameters (mass, centre of
gravity, and moment of inertia)
Steps for Inverse Dynamics
• Space diagram
of the lower
extremity
Divide Body into Segments and
Make Free-Body Diagrams
Make free-body
diagrams of
each segment
Add all Known Forces to FBD
• Weight (W)
• Ground
reaction
force (Fg)
Apply Newton’s Laws of
Motion to Terminal Segment
Start analysis
with terminal
segment(s),
e.g., foot or
hand
Apply Reactions of Terminal
Segment to Distal End of Next
Segment in Kinematic Chain
Continue to
next link in
the kinematic
chain, e.g.,
leg or
forearm
Repeat with Next segment in
Chain or Begin with Another Limb
Repeat until
all segments
have been
considered,
e.g., thigh or
arm
Compute Net Force and
Moment Powers
• Powers provided by the net moments of force
can be positive (increasing mechanical energy)
or negative (dissipation of mechanical energy),
or can show transfer of energy across joint
usually by muscles
Pmoment = M w
• Powers provided by net forces show rates of
transfer of energy from one segment to another
through joint connective tissues (ligaments) and
bone-on-bone (cartilage) contact
Pmoment = F  v
Normal Walking Example
•
•
•
•
•
•
•
Female subject
Laboratory walkway
Speed was 1.77 m/s (fast)
IFS = ipsilateral foot-strike
ITO = ipsilateral toe-off
CFS = contralateral foot-strike
CTO = contralateral toe-off
Ankle angular
velocity, moment
of force and
power
10
Dorsiflexion
0
-10
• Dorsiflexors
produce dorsiflexion
during swing
100
Trial: 2SFN3
Ang. velocity
Moment
Power
Dorsiflexors
0
-100
• Plantar flexors
control dorsiflexion
Plantar flexion
100
Plantar flexors
Concentric
0
• Large burst of
power by plantar
flexors for push-off
-100
Eccentric
-200CFS ITO
0.0
0.2
IFS CTO
0.4
0.6
Time (s)
CFS ITO
0.8
1.0
1.2
Knee angular
velocity, moment
of force and
power
10
Extension
0
-10 Flexion
• Negative work by
flexors to control
extension prior to
foot-strike
• Burst of power to
cushion landing
• Negative work by
extensors to control
flexion at push-off
100
Trial: 2SFN3
Ang. velocity
Moment
Power
Extensors
0
-100
100
Flexors
Concentric
0
-100
Eccentric
-200CFS ITO
0.0
0.2
IFS CTO
0.4
0.6
Time (s)
CFS ITO
0.8
1.0
1.2
Hip angular
velocity, moment
of force and
power
10
Flexion
0
-10
• Positive work by
flexors to swing leg
• Positive work by
extensors to extend
thigh
• Negative work by
flexors to control
extension
100
Extension
Trial: 2SFN3
Ang. velocity
Moment
Power
Flexors
0
-100
Extensors
Concentric
100
0
-100
Eccentric
-200CFS ITO
0.0
0.2
IFS CTO
0.4
0.6
Time (s)
CFS ITO
0.8
1.0
1.2
Solid-Ankle, Cushioned Heel
(SACH) Prostheses
Ankle angular
velocity, moment
of force and
power of SACH
foot prosthesis
10.
Dorsiflexing
0.
-10.
Plantar flexing
100.
• Power dissipation
during weight
acceptance and
push-off
• No power
produced during
push-off
Dorsiflexor
Trial: WB24MH-S
Ang. velocity
Net moment
Power
0.
-100.
100.
Plantar flexor
Concentric
0.
-100.
Eccentric
-200.
ITO
0.0
IFS CTO
0.2
0.4
0.6
0.8
Time (s)
CFS ITO
1.0
1.2
1.4
FlexFoot Prostheses
(Energy Storing)
Recent models
Original model
Ankle angular
velocity, moment
of force and
power of FlexFoot
prosthesis
10.
Dorsiflexing
0.
-10.
Plantar flexing
100.
Dorsiflexor
Trial: WB13MH-F
Ang. velocity
Net moment
Power
0.
• Power returned
during push-off
-100.
250.
Plantar flexor
Concentric
0.
-250.
Eccentric
-500.
ITO
0.0
IFS CTO
0.2
0.4
0.6
Time (s)
CFSITO
0.8
1.0
1.2
Ankle angular
velocity, moment
of force and
power of person
with hemiplegia
(normal side)
10.
Dorsiflexing
0.
-10.
Plantar flexing
100.
Dorsiflexor
Trial: WPN03EG
Ang. vel.
Net moment
Power
0.
• Power at push-off
is increased to
compensate for
other side
-100.
Plantar flexor
100.
Concentric
0.
-100.
-200.
Eccentric
IFS CTO
0.0
0.2
CFS
0.4
Time (s)
ITO
IFS
0.6
0.8
Ankle angular
velocity, moment
of force and
power of person
with hemiplegia
(stroke side)
• Reduced power
during push-off due
to muscle weakness
• Increased amount
of negative work
during stance
10.
Dorsiflexing
0.
-10.
Plantar flexing
100. Dorsiflexor
Trial: WPP14EG
Ang. vel.
Net moment
Power
0.
-100.
Plantar flexor
100. Concentric
0.
-100.
Eccentric
-200. IFS CTO
0.0
0.2
CFS ITO
0.4
Time (s)
IFS
0.6
0.8
Above-knee Prostheses
Questions?
Answers?
Comments?