Comparison of

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Comparison of Forefoot and Shoe Stiffness in
Running
USRP/Markin-Flanagan Presentation by
Daniel Adler Supervisor Dr. Peter Goldsmith
Mechanical Engineering
January 16, 2004
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Purpose

• Quantify human forefoot stiffness
• in running
• Measure running shoe stiffness in
• dynamic experiments
• Compare bending stiffness of
• forefoot with that of shoes

A B C
Running shoe design
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Definitions
MP joint metatarsophalangeal joint forefoot
ground reaction moment stiffness angular
deflection of MP shoe applied bending
moment stiffness angular deflection of shoe
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The Foot and the MP Joint

• Many models exist (rigid body, stiffness
  elements)
• Muscles near MP provide great relative power
• Range of motion highly subject-dependent
• More range in dorsiflexion than in plantar
  flexion
• MP joint is an energy absorber

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Dynamic Foot Stiffness Experiments

• 8 diverse subjects with markers on a right foot
• 6 high speed cameras (240 Hz) at various
  locations to capture position, rotation of foot
• force plate with 4 x-y-z load cells
• each subjects runs at 4 m/s 10 trials

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Subjects Tested
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Marker Locations
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Coordinate System
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Raw Data
Forces along Y axis (upward )
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Raw Data
Forces along X axis (forward )
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Raw Data
Moments about Z axis
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Errors
Weight bearing on sesamoid
Z-axis
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Computations
Angle about Z axis Angle vs. Moment
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Results
Stiffness vs. Deflection Angle
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Results

• During push-off stiffness rises sharply, then
• decreases steadily
• Forefoot behaves as an active, time-dependent
  mechanism
• Forefoot stiffness f(angle, time)
• Simple stiffness model is inadequate

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Shoe Bending Stiffness
Assumption Shoe stiffness acts in parallel with
foot stiffness
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Dynamic Experiments

• 4 different kinds of running shoes selected
• last fixed to shoe to restrict bending behind MP
  joint
• MTS machine applies downwards force at various
  rates
• (distance driven)

Sole length
A
B
Steel plate
Edge of plate
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Measurements
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Results shoe vs. foot stiffness
2.5 mm/s (static loading)
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Results shoe vs. foot stiffness
100 mm/s
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Results shoe vs. foot stiffness
250 mm/s (dynamic loading)
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Results

• Stiffness of each shoe relatively constant at
• lower speeds
• Stiffness varies considerably among shoes
• For bending range, human MP joint is much
• stiffer than shoe
• Combined stiffness dominated by foot
• Variations in shoe stiffness may not be critical
• to running (except in toe-off)

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Acknowledgements

• Mark Oleson
• Craig Sutherland
• (U of C Medical Research Centre)
• Dr. Goldsmith
• Dr. Stefanyshyn
• Markin-Flanagan Fund