Biomechanics of Walking

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Biomechanics of Walking

• D. Gordon E. Robertson, Ph.D.
• Biomechanics, Laboratory,
• School of Human Kinetics,
• University of Ottawa, Ottawa, CANADA

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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

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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

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Stride Analysis

• Stride characteristics
• stride vs. step length
• stride velocity stride (length/rate)
• stride width
• single/double support
• swing/stance ratio

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Electromyography
Noraxon system
Bortec system
Delsys electrodes
Mega system
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Stride Analysis
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Kinematic Analysis
Manual goniometer

• Linear position
• Ruler, tape measure, optical
• Angular position
• Protractor, inclinometer, goniometer
• Linear acceleration
• Accelerometry, videography
• Angular acceleration
• Videography

Miniature accelerometers
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Motion Analysis

• Cinefilm, video or infrared video
• Subject is filmed and locations of joint centres
  are digitized

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Computerized Digitizing Video (APAS)
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Stick Figure Animation
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Computerized Digitizing CCD (SIMI)
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Real-time Digitizing CCD (Vicon or Motion
Analysis)
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Full-body 3D Marker Set
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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)

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Force Platforms
Kistler force platforms
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Steps for Inverse Dynamics

• Space diagram of the lower extremity

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Divide Body into Segments and Make Free-Body
Diagrams

• Make free-body diagrams of each segment

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Add all Known Forces to FBD

• Weight (W)
• Ground reaction force (Fg)

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Apply Newtons Laws of Motion to Terminal Segment

• Start analysis with terminal segment(s), e.g.,
  foot or hand

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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

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Repeat with Next segment in Chain or Begin with
Another Limb

• Repeat until all segments have been considered,
  e.g., thigh or arm

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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

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Ankle angular velocity, moment of force and power
Dorsiflexion
Trial 2SFN3
Plantar flexion
Ang. velocity
Moment

• Dorsiflexors produce dorsiflexion during swing

Power
Dorsiflexors
Plantar flexors

• Plantar flexors control dorsiflexion

Concentric

• Large burst of power by plantar flexors for
  push-off

Eccentric
IFS
CTO
CFS
ITO
CFS
ITO
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Knee angular velocity, moment of force and power
Extension
Trial 2SFN3
Flexion
Ang. velocity

• Negative work by flexors to control extension
  prior to foot-strike

Moment
Power
Extensors
Flexors

• Burst of power to cushion landing

Concentric

• Negative work by extensors to control flexion at
  push-off

Eccentric
IFS
CTO
CFS
ITO
CFS
ITO
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Hip angular velocity, moment of force and power
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Flexion
0
Trial 2SFN3
Extension
-10
Ang. velocity
Moment

• Positive work by flexors to swing leg

Power
100
Flexors
0
Power (W) Moment (N.m)
A ng. Vel. (rad/s)
Extensors

• Positive work by extensors to extend thigh

-100
Concentric
100
0

• Negative work by flexors to control extension

Eccentric
-100
IFS
CTO
CFS
ITO
CFS
ITO
-200
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Time (s)
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Motion Analysis

• Cinefilm, video or infrared video
• Athlete is filmed and locations of joint centres
  are digitized
• body is modeled as a system of connected segments

high-speed cine-camera
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Stick Figure of Sprinter
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Start Phase

• No motion permitted when gun sounds
• No force on blocks 0.10 seconds before gun sounds
• Gun fires and there is a delay before sprinter
  hears gun (unless blocks have speakers)
• Delay between when gun fires and force is applied
  to blocks (time for message to reach muscles at 6
  m/s)
• Taller sprinters take longer to start

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Acceleration Phase

• Each athlete has his/her own rate of acceleration
• The whole race takes between 43 and 48 steps
• At maximum speed, stride length (1 stride 2
  steps) is over 4.5 metres long!
• Can last to 70 metres

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Last 60 Metres of Race
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Constant Velocity Phase

• athletes achieve maximum, constant velocity
  between 50 and 70 metres
• speed
• 9 12 metres / second
• 32 43 kilometres / hour
• foot achieves twice this velocity (86 km/h!)

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Fastest Sprinter (in 1996)Johnson or Bailey?

• Johnsons 200 m record 19.32 s
• Each half 9.66 s?
• Baileys 100 m record 9.84 s
• US reporters claimed Johnson was faster?
• Johnson had running start for last 100 m
• At 12 m/s Bailey runs 100 m in 8.33 s, 200 m
  time could be 18.17 (new WR)!
• race in Toronto confirmed Bailey was Fastest Man
  in the World

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Stride Analysis

• swing phase of one leg
• world-class male sprinter
• 50 m into 100 m competitive race (t 10.06 s)
• analysis of hip and knee only (ankle forces not
  significant during swing)

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• Hip angular velocity power
• initial burst of power to create swing
• 3000-4000 W peak power by iliopsoas and rectus
  femoris
• latter burst to drive leg down
• 2800-3600 W peak power by gluteals

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• Knee angular velocity power
• initial burst of power to stop flexion by muscle
  block not by knee muscles
• small burst for extension
• final burst to stop extension by eccentric
  contraction of hamstrings

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Questions?

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Questions?

• Answers?
• Comments?

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