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

Quantitative Domains Temporal Electromyography 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

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

Donovan Bailey sets world record (9 Donovan Bailey sets world record (9.835) despite slowest reaction time (0.174) of finalists

Electromyography Bortec system Noraxon system Delsys electrodes Mega system

EMG of normal walking gait initiation strides rectus femoris vastus lateralis tibialis anterior gastrocnemius biceps femoris heel switch

EMG of normal walking rectus femoris vastus lateralis rectus femoris contracts twice per cycle, once in early stance and once in late stance rectus femoris vastus lateralis tibialis anterior gastrocnemius biceps femoris heel switch

EMG of normal walking rectus femoris vastus lateralis biceps femoris has one longer contraction in late swing and early stance, synchronous with one burst of rectus femoris tibialis anterior gastrocnemius biceps femoris heel switch

EMG of normal walking tibialis anterior has two bursts of activity one in mid-swing and one during early stance. It is very active at initiation. rectus femoris vastus lateralis tibialis anterior gastrocnemius biceps femoris heel switch

EMG of normal walking gastrocnemius has one long contraction throughout stance. It is asynchronous with tibialis anterior. rectus femoris vastus lateralis tibialis anterior gastrocnemius biceps femoris heel switch

Kinematic Analysis Linear position Linear velocity Linear acceleration Ruler, tape measure, optical, potentiometric Linear velocity radar gun, photo-optical timer Linear acceleration Accelerometry, videography 3D digitizer radar gun miniature accelerometers

Gait Characteristics - Walking

Gait Characteristics – Running/Sprinting

Motion Capture Cinefilm, video or infrared video Basler charge-coupled device (CCD) camera Cinefilm, video or infrared video Subject is filmed and locations of joint centres are digitized Panasonic videocamera Vicon infra-red camera

Video Motion Capture (e.g., SIMI or APAS) data F-Scan data EMG data 3D motion data Force platform data

Passive Infrared Motion Capture (e.g., M.A.C.) Infrared video cameras M.A.C. system Kistler force platforms

Active Infrared Motion Capture NDI’s Optotrak Infrared video cameras Infrared emitting diodes

Computerized Digitizing (Vicon, SIMI, etc.)

Gait and Movement Analysis Lab (e.g., Vicon) Vicon Nexus or Workstation Vicon MX cameras Kistler and AMTI force platforms Bortec EMGs ( 8-channels) or Delsys Trigo (16 EMGs + 24 accelerometers) Tekscan or Pedar in-shoe pressure mapping systems

Full-body 3D Marker Set

3D Geometric Model (Visual3D) from stick-figures to geometrical solids of revolution with known inertial properties from markers to joint centres and stick-figure of body

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)

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

Compute Net Force and Moment Powers Powers provided by the net moments of force can be positive (increasing mechanical energy) or negative (dissipation of mechanical energy), or can show transfer of energy across joint usually by muscles Pmoment = M w Powers provided by net forces show rates of transfer of energy from one segment to another through joint connective tissues (ligaments) and bone-on-bone (cartilage) contact Pmoment = F  v

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 Plantar flexors control dorsiflexion Concentric Large burst of power by plantar flexors 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

Above-knee Prostheses

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