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Biomechanics of WalkingBiomechanics of Walking
D. Gordon E. Robertson, PhD, FCSB
Biomechanics, Laboratory,
School of Human Kinetics,
University of Ottawa, Ottawa, Canada
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 (foot-
strike, 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
Delsys electrodes Mega system
Noraxon systemBortec system
EMG of normal walking
gait initiation
rectus femoris
vastus lateralis
tibialis anterior
gastrocnemius
biceps femoris
heel switch
strides
EMG of normal walking
rectus femoris
vastus lateralis
tibialis anterior
gastrocnemius
biceps femoris
heel switch
rectus femoris contracts twice per cycle, once in early stance and once in late stance
EMG of normal walking
rectus femoris
vastus lateralis
tibialis anterior
gastrocnemius
biceps femoris
heel switch
biceps femoris has one longer contraction in late swing and early stance, synchronous with one burst of rectus femoris
EMG of normal walking
rectus femoris
vastus lateralis
tibialis anterior
gastrocnemius
biceps femoris
heel switch
tibialis anterior has two bursts of activity one in mid-swing and one during early stance. It is very active at initiation.
EMG of normal walking
rectus femoris
vastus lateralis
tibialis anterior
gastrocnemius
biceps femoris
heel switch
gastrocnemius has one long contraction throughout stance.
It is asynchronous with tibialis anterior.
Kinematic Analysis
• Linear position– Ruler, tape measure, optical,
potentiometric
• Linear velocity– radar gun, photo-optical timer
• Linear acceleration– Accelerometry, videography
miniature accelerometers
3D digitizer
radar gun
Gait Characteristics - Walking
stride length step length
left foot
swing phase,left foot
right foot
stance phase,left foot
single-support
left toe-off
one gait cycle
time
double-supportleft foot-strike
right foot-strikeright toe-off
a
b
walking
step width
Gait Characteristics – Running/Sprinting
stride length step length
left foot
swing phase,left foot
right foot
stance phase,left foot
left toe-off
one gait cycle
timeleft foot-strike right foot-strikeright toe-off
a
b
running/sprinting
flight phase
Motion Capture
• Cinefilm, video or infrared video
• Subject is filmed and locations of joint centres are digitized
Panasonic videocamera
Basler charge-coupled device (CCD) camera
Vicon infra-red camera
Video Motion Capture(e.g., SIMI or APAS)
3D motiondata
EMG data
F-Scandata
Force platformdata
Videodata
Passive InfraredMotion Capture
(e.g., M.A.C.)
Infrared video cameras
Kistler force platforms
M.A.C.system
Active InfraredMotion Capture
• NDI’s Optotrak
Infrared video cameras
Infrared emitting 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 ( 8-channels) or Delsys Trigo (16 EMGs + 24 accelerometers)
• Tekscan or Pedar in-shoe pressure mapping systems
Full-body 3D Marker Set
3D Geometric Model(Visual3D)
from stick-figures to geometrical solids of revolution with known inertial properties
from markers to joint centres and stick-figure of body
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 • 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
• Dorsiflexors produce dorsiflexion during swing
• Plantar flexors control dorsiflexion
• Large burst of power by plantar flexors for push-off 0.0 0.2 0.4 0.6 0.8 1.0 1.2
Time (s)
-200
-100
0
100
-100
0
100
-10
0
10
P
ow
er
(W)
Mo
me
nt
(N.m
)
A
ng
. V
el.
(ra
d/s
)
Trial: 2SFN3Ang. velocityMomentPower
CFS ITO IFS CTO CFS ITO
Dorsiflexion
Plantar flexion
Dorsiflexors
Plantar flexors
Concentric
Eccentric
Knee angular velocity, moment of force and power
• Negative work by extensors to control flexion at push-off
• Burst of power to cushion landing
• Negative work by flexors to control extension prior to foot-strike
0.0 0.2 0.4 0.6 0.8 1.0 1.2Time (s)
-200
-100
0
100
-100
0
100
-10
0
10
P
ow
er
(W)
M
om
en
t (N
.m)
A
ng
. V
el.
(ra
d/s
)
Trial: 2SFN3Ang. velocityMomentPower
CFS ITO IFS CTO CFS ITO
Extension
Flexion
Extensors
Flexors
Concentric
Eccentric
Hip angular velocity, moment of force and power
0.0 0.2 0.4 0.6 0.8 1.0 1.2Time (s)
-200
-100
0
100
-100
0
100
-10
0
10
P
ow
er
(W)
Mo
me
nt
(N.m
)
A
ng
. V
el.
(ra
d/s
)
Trial: 2SFN3Ang. velocityMomentPower
CFS ITO IFS CTO CFS ITO
Flexion
Extension
Flexors
Extensors
Concentric
Eccentric
• Positive work by flexors to swing leg
• Positive work by extensors to extend thigh
• Negative work by flexors to control extension
Solid-Ankle, Cushioned Heel (SACH) Prostheses
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Time (s)
-200.
-100.
0.
100.
-100.
0.
100.
-10.
0.
10.
Po
we
r (W
)
Mo
me
nt
(N.m
)
An
gu
lar
ve
l. (
/s)
Ankle angular velocity, moment of force and power of SACH foot prosthesis
• No power produced during push-off
Trial: WB24MH-SAng. velocityNet momentPower
ITO IFS CTO CFS ITO
Dorsiflexing
Plantar flexing
Dorsiflexor
Plantar flexor
Concentric
Eccentric
• Power dissipation during weight acceptance and push-off
FlexFoot Prostheses(Energy Storing)
Recent models
Original model
Ankle angular velocity, moment of force and power of FlexFoot prosthesis
• Power returned during push-off
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Time (s)
-500.
-250.
0.
250.
-100.
0.
100.
-10.
0.
10.
Po
we
r (W
)
M
om
en
t (N
.m)
A
ng
ula
r v
el.
(/s
)
Trial: WB13MH-FAng. velocityNet momentPower
ITO IFS CTO CFS ITO
Dorsiflexing
Plantar flexing
Dorsiflexor
Plantar flexor
Concentric
Eccentric
Ankle angular velocity, moment of force and power of person with hemiplegia (normal side)
• Power at push-off is increased to compensate for other side
0.0 0.2 0.4 0.6 0.8Time (s)
-200.
-100.
0.
100.
-100.
0.
100.
-10.
0.
10.
Po
we
r (W
)
M
om
en
t (N
.m)
A
ng
ula
r v
el.
(/s
)
Trial: WPN03EGAng. vel.Net momentPower
IFS CTO CFS ITO IFS
Dorsiflexing
Plantar flexing
Dorsiflexor
Plantar flexor
Concentric
Eccentric
Ankle angular velocity, moment of force and power of person with hemiplegia (stroke side)
• Reduced power during push-off due to muscle weakness
0.0 0.2 0.4 0.6 0.8Time (s)
-200.
-100.
0.
100.
-100.
0.
100.
-10.
0.
10.
Po
we
r (W
)
M
om
en
t (N
.m)
A
ng
ula
r v
el.
(/s
)
Trial: WPP14EGAng. vel.Net momentPower
IFS CTO CFS ITO IFS
Dorsiflexing
Plantar flexing
Dorsiflexor
Plantar flexor
Concentric
Eccentric
• Increased amount of negative work during stance
Above-knee Prostheses
Questions?
Answers?
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