Two-segment Model of the Foot for Gait Analysis D. Gordon E. Robertson, Ph.D. Alison Cronin Biomechanics Laboratory, School of Human Kinetics, University of Ottawa, Ottawa, CANADA
Introduction Stephanyshn & Nigg (1997) showed negative work done by MP plantar flexors for running used EMED insole pressure system to partition floor reactions into two components pressure systems have no ability to distinguish components of a force only the magnitude of the resultant a single force platform cannot distinguish among several applied forces force plates computes a single resultant force--its components and centre of pressure
Solution use two force platforms Gerber & Stuessi (1987) developed equations to combine multiple force plates (available at biomech/csb/archives/ kistler.pdf) arrange plates end-to- end
Solution subject lands foot across both plates in most cases little or no force occurs midstance can evaluate the subject using one or two ground reaction forces
Methods two male subjects video taped at 60 fields/second five trials of stance phase of walking at self- selected speed ground reaction forces sampled at 250 Hz from two Kistler force plates two conditions: –one segment foot –two segment foot
Free-body diagram of one-segment foot
Free-body diagrams of two-segment foot
Methods mechanical energy and rate of change of energy computed ( E/ t) inverse dynamics to calculate net forces (F) and moments of force (M) force powers:P f = F. v moment powers:P m = M total power:Pt = Pf + Pm power imbalance:Pi = E/ t - Pt
Results (subject 1) pause to show animation
Ang. velocity, moment and power of the ankle joint (WN01GR) Time (s) Power (W) Moment (N.m) Angular vel. (/s) Trial: WN01GR Ang. vel. Net moment Power IFS IHO ITO Dorsiflexing Plantar flexing Dorsiflexor Plantar flexor Concentric Eccentric
Ang. velocity, moment and power of the ankle joint (WN01GR2) Time (s) Power (W) Moment (N.m) Angular vel. (/s) Trial: WN01GR2 Ang. vel. Net moment Power IFS IHO ITO Dorsiflexing Plantar flexing Dorsiflexor Plantar flexor Concentric Eccentric
Ang. velocity, moment and power of the MP joint (WN01GR2) Time (s) Power (W) Moment (N.m) Angular vel. (/s) Trial: WN01GR2 Ang. vel. Net moment Power IFS IHO ITO Dorsiflexing Plantar flexing Dorsiflexor Plantar flexor Concentric Eccentric
Foot powers (WN01GR) Time (seconds) Power (W) Trial: WN01GR Floor power Force power Moment power Total power Energy rate Power imbalance IFS IHO ITO
Time (seconds) Power (W) Trial: WN01GR2 Floor power MP force power MP moment power Ff total power Ff energy rate Ff power imbalance IFS IHO ITO Forefoot powers (WN01GR2)
Rearfoot powers (WN01GR2) Time (seconds) Power (W) Trial: WN01GR2 MP force power MP moment power Ankle force power Ankle moment power Rf total power Rf energy rate Rf power imbalance IFS IHO ITO
Results (subject 2) pause to show animation
Ang. velocity, moment and power of the ankle joint (WN01JS) Time (s) Power (W) Moment (N.m) Angular vel. (/s) Trial: WN01JS Ang. vel. Net moment Power IFS IHO ITO Dorsiflexing Plantar flexing Dorsiflexor Plantar flexor Concentric Eccentric
Ang. velocity, moment and power of the MP joint (WN01JS2) Time (s) Power (W) Moment (N.m) Angular vel. (/s) Trial: WN01JS2 Ang. vel. Net moment Power IFS IHO ITO Dorsiflexing Plantar flexing Dorsiflexor Plantar flexor Concentric Eccentric
Ang. velocity, moment and power of the ankle joint (WN01JS2) Time (s) Power (W) Moment (N.m) Angular vel. (/s) Trial: WN01JS2 Ang. vel. Net moment Power IFS IHO ITO Dorsiflexing Plantar flexing Dorsiflexor Plantar flexor Concentric Eccentric
Foot powers (WN01JS) Time (seconds) Power (W) Trial: WN01JS Floor power Force power Moment power Total power Energy rate Power imbalance IFS IHO ITO
Forefoot powers (WN01JS2) Time (seconds) Power (W) Trial: WN01JS2 Floor power MP force power MP moment power Ff total power Ff energy rate Ff power imbalance IFS IHO ITO
Rearfoot powers (WN01JS2) Time (seconds) Power (W) Trial: WN01JS2 MP force power MP moment power Ankle force power Ankle moment power Rf total power Rf energy rate Rf power imbalance IFS IHO ITO
Conclusions adding MP joint reduces error at foot- strike and toe-off plantar flexor moment at MP joint does both negative and positive work, but mainly negative
Questions? Answers! Where to go next?
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