1. Biomechanics of Walking and Stair Ascent and Descent D. Gordon E. Robertson, Ph.D. Biomechanics, Laboratory, School of Human Kinetics, University of Ottawa, Ottawa, CANADA

2. Quantitative Domains Temporal –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

3. 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

4. Motion Analysis Tools EMG Force platform Cine or Video camera

5. Electromyography Delsys system Mega system Noraxon systemBortec system

6. Kinematic Analysis Study of motion without consideration of its causes Motion description Based on Calculus developed by Newton and Leibnitz Isaac Newton, 1642-1727

7. Kinematic Analysis Linear position –Ruler, tape measure, optical Angular position –Protractor, inclinometer, goniometer Linear acceleration –Accelerometry, videography Angular acceleration –Videography Miniature accelerometers Manual goniometer

8. Motion Analysis Cinefilm, video or infrared video Subject is filmed and locations of joint centres are digitized High-speed cinecamera Videocamera Infrared camera

9. Computerized Digitizing (APAS)

10. Computerized Digitizing (Simi)

11. Stick Figure Animation Walking

12. 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)

13. Force Platforms 2 Kistler force platforms Ground reaction force

14. Steps for Inverse Dynamics Space diagram of the lower extremity

15. Divide Body into Segments and Make Free-Body Diagrams Make free- body diagrams of each segment

16. Add all Known Forces to FBD Weight (W) Ground reaction force (F g )

17. Apply Newton’s Laws of Motion to Terminal Segment Start analysis with terminal segment(s), e.g., foot or hand

18. 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

19. Repeat with Next segment in Chain or Begin with Another Limb Repeat until all segments have been considered, e.g., thigh or arm

20. Joint Power Analysis compute the net moment of force at the joint multiply angular velocity and moment of force to obtain the “moment power” this is the power produced by the net moment of force acting across the joint it is mainly caused by muscle forces compute the angular velocity of the joint

21. Normal Walking Example Female subject Laboratory walkway Speed was 1.77 m/s IFS = ipsilateral foot-strike ITO = ipsilateral toe-off CFS = contralateral foot-strike CTO = contralateral toe-off

22. Ankle angular velocity, moment of force and power Dorsiflexors produce dorsiflexion during swing Plantar flexors control dorsiflexion Large burst of power by plantar flexors for push-off Trial: 2SFN3 Ang. velocity Moment Power CFS ITO IFS CTO CFS ITO Dorsiflexion Plantar flexion Dorsiflexors Plantar flexors Concentric Eccentric

23. Knee angular velocity, moment of force and power Negative work by extensors to control flexion at push-off Burst of power to cushion landing Negative work by flexors to control extension prior to foot-strike Trial: 2SFN3 Ang. velocity Moment Power CFS ITO IFS CTO CFS ITO Extension Flexion Extensors Flexors Concentric Eccentric

24. Hip angular velocity, moment of force and power 0.00.20.40.60.81.01.2 Time (s) -200 -100 0 100 -100 0 100 -10 0 10 Power (W) Moment (N.m) A ng. Vel. (rad/s) Trial: 2SFN3 Ang. velocity Moment Power CFS ITO IFS CTO CFS ITO Flexion Extension Flexors Extensors Concentric Eccentric Positive work by flexors to swing leg Positive work by extensors to extend thigh Negative work by flexors to control extension

25. Solid-Ankle, Cushioned Heel (SACH) Prostheses

26. Stick Figure Animation Walking with SACH foot

27. Ankle angular velocity, moment of force and power of SACH foot prosthesis No power produced during push-off Trial: WB24MH-S Ang. velocity Net moment Power ITO IFS CTO CFS ITO Dorsiflexing Plantar flexing Dorsiflexor Plantar flexor Concentric Eccentric Power dissipation during weight acceptance and push-off

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

29. Stick Figure Animation Walking with FlexFoot prosthesis

30. Ankle angular velocity, moment of force and power of FlexFoot prosthesis Power returned during push-off Trial: WB13MH-F Ang. velocity Net moment Power ITO IFS CTO CFS ITO Dorsiflexing Plantar flexing Dorsiflexor Plantar flexor Concentric Eccentric

31. Ankle angular velocity, moment of force and power of person with hemiplegia (stroke side) No power during push-off

32. Ankle angular velocity, moment of force and power of person with hemiplegia (normal side) Power at push-off is reduced due to slower gait Trial: WPN03EG Ang. vel. Net moment Power IFS CTO CFS ITO IFS Dorsiflexing Plantar flexing Dorsiflexor Plantar flexor Concentric Eccentric Negative power is also reduced

33. Other Gait Patterns Above-knee Prostheses

34. Stick Figure Animation Walking with Terry Fox prosthesis

35. Support Moment Used to quantify stability during stance of gait Sum of ankle, knee and hip moments Extensors moments are made positive M support = M ankle + M knee + M hip Should remain positive throughout stance despite loss of function at one or more joints Studies have shown that even people with artificial joints produce a positive support moment throughout stance (Winter, J. Biomech, 13, 923-927, 1980)

36. Support Moment during Walking Support moment is positive throughout stance Typically has two peaks one after IFS and one before ITO Ankle plantar flexors are the most important from midstance to toe-off

37. Laboratory Stairs Step height = 24 cm Step tread = 30 cm Railings = 36 in. Height and tread are adjustable Force platforms

38. Stick Figure Animation Up One Step from Landing

39. Smaller ankle plantar flexor moment Larger than normal knee extensor moment 0.70.91.11.31.51.71.92.12.3 Time (seconds) -200. -100. 0. 100. -100. 0. 100. -100. 0. 100. -100. 0. 100. 200. Net moments of force (N.m) Trial: STLUP7RH ITO IFS ITO Support moment Hip extensor Knee extensor Ankle extensor Support moment similar to walking

40. Similarities to Walking Double support periods Ground reaction forces have double peak Cadence similar Support moment is similar (always positive with two peaks)

41. Differences with Walking Peak forces slightly higher Centre of pressure is concentrated under metatarsals, rarely near heel Several types of steps –ascent versus descent –single step up and down –double step up and down –start from or end at a landing Step height and tread vary from stairway to stairway Railings may be present

42. Ascent versus Descent Descent is more dangerous because if tripping occurs person will fall farther Descent is more likely to cause fall since centre of pressure and centre of gravity is closer to edge of stair

43. Factors Influencing Stability Weight Size of base of support (hand rails) Friction Distance from tipping edge Height of centre of gravity Visual field Vestibular system Inebriation/drugs

44. Stick Figure Animation Down Two Stairs to Landing

45. Down Two Stairs Forwards Larger than normal negative power by ankle plantar flexors after foot-strike (IFS) 0.70.91.11.31.51.71.92.1 Time (seconds) -500. -250. 0. 250. 500. -250. 0. 250. -250. 0. 250. 500. Power (watts) Trial: CJRFD ITO IFS ITO Hip powers Knee powers Ankle powers Positive work done after IFS by knee flexors

46. Possibly Safer Descent Descend backwards Centre of pressure and centre of gravity are farther from edge of stairs If tripping occurs person falls into stairs not down stairs Person will be “forced” to use railing Problem with seeing next step Some people may have problem with neck

47. Stick Figure Animation Down Two Steps Backwards

48. Down Two Stairs Backwards No concentric knee power required after IFS Larger than normal negative power by ankle plantar flexors after foot-strike (IFS) No push-off power needed from ankle

49. What’s Next Modify rise and tread At-risk subjects –Elderly –Infants –Disabled –Distracted –Prostheses –Robots Ramps versus stairs –Angle of ramp –Surface friction Cambered surfaces

50. Questions? Answers? Comments?