Biomechanics of Walking D. Gordon E. Robertson, PhD, FCSB Biomechanics, Laboratory, School of Human Kinetics, University of Ottawa, Ottawa, Canada

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

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

Motion Analysis Tools EMG Cine or Video camera Force platform

Electromyography Bortec system 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 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

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

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 (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

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 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

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

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)

Solid-Ankle, Cushioned Heel (SACH) Prostheses

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

FlexFoot Prostheses (Energy Storing) Original model FlexFoot Prostheses (Energy Storing) Recent models

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)

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)

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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