1. 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

2. 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

3. Solution use two force platforms Gerber & Stuessi (1987) developed equations to combine multiple force plates (available at www.health.uottawa.ca/ biomech/csb/archives/ kistler.pdf) arrange plates end-to- end

4. 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

5. 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

6. Free-body diagram of one-segment foot

7. Free-body diagrams of two-segment foot

8. 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

9. Results (subject 1) pause to show animation

10. Ang. velocity, moment and power of the ankle joint (WN01GR) 0.00.10.20.30.40.50.60.70.8 Time (s) -500. -250. 0. 250. -100. 0. 100. -10. 0. 10. 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

11. Ang. velocity, moment and power of the ankle joint (WN01GR2) 0.00.10.20.30.40.50.60.70.8 Time (s) -500. -250. 0. 250. -100. 0. 100. -10. 0. 10. 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

12. Ang. velocity, moment and power of the MP joint (WN01GR2) 0.00.10.20.30.40.50.60.70.8 Time (s) -500. -250. 0. 250. -100. 0. 100. -10. 0. 10. 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

13. Foot powers (WN01GR) 0.000.100.200.300.400.500.600.70 Time (seconds) -2000. -1500. -1000. -500. 0. 500. 1000. 1500. 2000. Power (W) Trial: WN01GR Floor power Force power Moment power Total power Energy rate Power imbalance IFS IHO ITO

14. 0.000.100.200.300.400.500.600.70 Time (seconds) -2000. -1500. -1000. -500. 0. 500. 1000. 1500. 2000. 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)

15. Rearfoot powers (WN01GR2) 0.000.100.200.300.400.500.600.70 Time (seconds) -2000. -1500. -1000. -500. 0. 500. 1000. 1500. 2000. 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

16. Results (subject 2) pause to show animation

17. Ang. velocity, moment and power of the ankle joint (WN01JS) 0.00.10.20.30.40.50.60.70.80.91.0 Time (s) -500. -250. 0. 250. -100. 0. 100. -10. 0. 10. 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

18. Ang. velocity, moment and power of the MP joint (WN01JS2) 0.00.10.20.30.40.50.60.70.80.91.0 Time (s) -500. -250. 0. 250. -100. 0. 100. -10. 0. 10. 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

19. Ang. velocity, moment and power of the ankle joint (WN01JS2) 0.00.10.20.30.40.50.60.70.80.91.0 Time (s) -500. -250. 0. 250. -100. 0. 100. -10. 0. 10. 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

20. Foot powers (WN01JS) 0.000.100.200.300.400.500.600.700.800.90 Time (seconds) -2000. -1500. -1000. -500. 0. 500. 1000. 1500. 2000. Power (W) Trial: WN01JS Floor power Force power Moment power Total power Energy rate Power imbalance IFS IHO ITO

21. Forefoot powers (WN01JS2) 0.000.100.200.300.400.500.600.700.800.90 Time (seconds) -2000. -1500. -1000. -500. 0. 500. 1000. 1500. 2000. Power (W) Trial: WN01JS2 Floor power MP force power MP moment power Ff total power Ff energy rate Ff power imbalance IFS IHO ITO

22. Rearfoot powers (WN01JS2) 0.000.100.200.300.400.500.600.700.800.90 Time (seconds) -2000. -1500. -1000. -500. 0. 500. 1000. 1500. 2000. 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

23. 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

24. Questions? Answers! Where to go next?

25. Thank you