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Biomechanics of Walking
D. Gordon E. Robertson, PhD, FCSB Biomechanics, Laboratory, School of Human Kinetics, University of Ottawa, Ottawa, Canada
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Quantitative Domains Temporal Kinematic (motion description)
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
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Temporal Analysis Stride time Stride rate = 1/rate
Stride cadence = 120 x rate (b/min) Instrumentation Photocells and timers Videography (1 frame = /30 second) Metronome
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Motion Analysis Tools EMG Cine or Video camera Force platform
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Electromyography Bortec system Noraxon system Delsys electrodes
Mega system
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Kinematic Analysis Study of motion without consideration of its causes
Motion description Based on Calculus developed by Newton and Leibnitz Isaac Newton,
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Kinematic Analysis Linear position Angular position
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
High-speed cine-camera Cinefilm, video or infrared video Subject is filmed and locations of joint centres are digitized Videocamera Infra-red camera
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Computerized Digitizing (APAS)
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Stick Figure Animation
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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 Newton’s 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
0.0 0.2 0.4 0.6 0.8 1.0 1.2 Time (s) -200 -100 100 -10 10 Power (W) Moment (N.m) Ang. Vel. (rad/s) Dorsiflexion Plantar flexion Trial: 2SFN3 Ang. velocity Moment Dorsiflexors produce dorsiflexion during swing Power Dorsiflexors Plantar flexors Plantiflexors control dorsiflexion Concentric Large burst of power by plantiflexors for push-off Eccentric CFS ITO IFS CTO CFS ITO
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Knee angular velocity, moment of force and power
0.0 0.2 0.4 0.6 0.8 1.0 1.2 Time (s) -200 -100 100 -10 10 Power (W) Moment (N.m) Ang. Vel. (rad/s) Extension Flexion Trial: 2SFN3 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 CFS ITO IFS CTO CFS ITO
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Hip angular velocity, moment of force and power
10 Flexion -10 Extension Trial: 2SFN3 Ang. velocity Moment Positive work by flexors to swing leg Power 100 Flexors Power (W) Moment (N.m) A ng. Vel. (rad/s) Positive work by extensors to extend thigh Extensors -100 Concentric 100 Negative work by flexors to control extension Eccentric -100 -200 CFS ITO IFS CTO CFS ITO 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Time (s)
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Solid-Ankle, Cushioned Heel (SACH) Prostheses
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Power dissipation during weight acceptance and push-off
Ankle angular velocity, moment of force and power of SACH foot prosthesis 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Time (s) -200. -100. 0. 100. -10. 10. Power (W) Moment (N.m) Angular vel. (/s) Dorsiflexing Trial: WB24MH-S Plantar flexing Ang. velocity Net moment Dorsiflexor Power Power dissipation during weight acceptance and push-off Plantar flexor Concentric No power produced during push-off Eccentric ITO IFS CTO CFS ITO
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FlexFoot Prostheses (Energy Storing)
Original model FlexFoot Prostheses (Energy Storing) Recent models
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Power returned during push-off
Ankle angular velocity, moment of force and power of FlexFoot prosthesis -100. 0. 100. -10. 10. Power (W) Moment (N.m) Angular vel. (/s) Dorsiflexing Trial: WB13MH-F Plantar flexing Ang. velocity Net moment Dorsiflexor Power Power returned during push-off Plantar flexor Concentric 250. 0. -250. Eccentric ITO IFS CTO CFS ITO -500. 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Time (s)
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Power at push-off is increased to compensate for other side
Ankle angular velocity, moment of force and power of person with hemiplegia (normal side) 10. Dorsiflexing 0. -10. Trial: WPN03EG Plantar flexing Ang. vel. Net moment 100. Dorsiflexor Power 0. Power at push-off is increased to compensate for other side Power (W) Moment (N.m) Angular vel. (/s) -100. Plantar flexor 100. Concentric 0. -100. Eccentric IFS CTO CFS ITO IFS -200. 0.0 0.2 0.4 0.6 0.8 Time (s)
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Reduced power during push-off due to muscle weakness
Ankle angular velocity, moment of force and power of person with hemiplegia (stroke side) 0.0 0.2 0.4 0.6 0.8 Time (s) -200. -100. 0. 100. -10. 10. Power (W) Moment (N.m) Angular vel. (/s) Dorsiflexing Trial: WPP14EG Plantar flexing Ang. vel. Net moment Dorsiflexor Power Reduced power during push-off due to muscle weakness Plantar flexor Concentric Increased amount of negative work during stance Eccentric IFS CTO CFS ITO IFS
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Questions? Answers? Comments?
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