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
(foot-strike, toe-off), stride rate
•
Kinematic (motion description)
– stride length, velocity, ranges of motion, acceleration
•
Kinetic (causes of motion)
– ground reaction forces, joint forces, moments of force, work, energy and power

Temporal Analysis
•
Stride time
•
Stride rate = 1/rate
•
Stride cadence = 120 x rate (b/min)
•
Instrumentation
– Photocells and timers
– Videography (1 frame =
1/30 second)
– Metronome

EMG
Motion Analysis Tools
Cine or
Video camera
Force platform

Bortec system
Electromyography
Noraxon system
Delsys electrodes Mega system

Kinematic Analysis
•
Study of motion without consideration of its causes
•
Motion description
•
Based on Calculus developed by Newton and Leibnitz
Isaac Newton, 1642-1727

Kinematic Analysis
Manual goniometer
• Linear position
– Ruler, tape measure, optical
•
Angular position
– Protractor, inclinometer, goniometer
•
Linear acceleration
– Accelerometry, videography
•
Angular acceleration
– Videography
Miniature accelerometers

Motion Analysis
High-speed cine-camera
•
Cinefilm, video or infrared video
•
Subject is filmed and locations of joint centres are digitized
Videocamera
Infra-red camera

Computerized Digitizing
(APAS)

Stick Figure Animation

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)

Force Platforms
Kistler force platforms

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 (F g
)

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

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
• Plantiflexors control dorsiflexion
• Large burst of power by plantiflexors for push-off
10
Dorsiflexion
0
-10
Plantar flexion
100
Dorsiflexors
0
-100
Plantar flexors
Trial: 2SFN3
Ang. velocity
Moment
Power
100
Concentric
0
-100
Eccentric
-200
CFS ITO
0.0
0.2
IFS CTO
0.4
0.6
Time (s)
0.8
CFS ITO
1.0
1.2

Knee angular velocity, moment of force and power
• 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
10
Extension
0
-10
Flexion
100
Extensors
0
-100
Flexors
Trial: 2SFN3
Ang. velocity
Moment
Power
100
Concentric
0
-100
Eccentric
-200
CFS ITO
0.0
0.2
IFS CTO
0.4
0.6
Time (s)
0.8
CFS ITO
1.0
1.2

Hip angular velocity, moment of force and power
• Positive work by flexors to swing leg
• Positive work by extensors to extend thigh
• Negative work by flexors to control extension
10
Flexion
0
-10
Extension
100
Flexors
0
-100
Extensors
100
Concentric
Trial: 2SFN3
Ang. velocity
Moment
Power
0
-100
Eccentric
-200
CFS ITO
0.0
0.2
IFS CTO
0.4
0.6
Time (s)
0.8
CFS ITO
1.0
1.2

Solid-Ankle, Cushioned Heel
(SACH) Prostheses

Ankle angular velocity, moment of force and power of SACH foot prosthesis
• Power dissipation during weight acceptance and push-off
• No power produced during push-off
10.
Dorsiflexing
0.
-10.
100.
Plantar flexing
Dorsiflexor
0.
-100.
100.
Plantar flexor
Concentric
Trial: WB24MH-S
Ang. velocity
Net moment
Power
0.
-100.
Eccentric
-200.
ITO IFS CTO CFS ITO
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Time (s)

FlexFoot Prostheses
(Energy Storing)
Original model
Recent models

Ankle angular velocity, moment of force and power of FlexFoot prosthesis
• Power returned during push-off
10.
Dorsiflexing
0.
-10.
100.
Plantar flexing
Dorsiflexor
Trial: WB13MH-F
Ang. velocity
Net moment
Power
0.
-100.
250.
Plantar flexor
Concentric
0.
-250.
Eccentric
-500.
0.0
ITO
0.2
IFS CTO
0.4
0.6
Time (s)
0.8
CFSITO
1.0
1.2

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
10.
Dorsiflexing
0.
-10.
100.
Plantar flexing
Dorsiflexor
0.
Trial: WPN03EG
Ang. vel.
Net moment
Power
-100.
100.
Plantar flexor
Concentric
0.
-100.
-200.
0.0
Eccentric
IFS CTO
0.2
CFS ITO
0.4
Time (s)
0.6
IFS
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)
0.6
IFS
0.8

Answers?
Questions?
Comments?