Biomechanics of Walking D. Gordon E. Robertson, PhD, FCSB Biomechanics, Laboratory, School of Human...

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

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Answers?

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