Biomechanics and Stair and Ramp Ascent and Descent D. Gordon E. Robertson, Ph.D. Edward Lemaire, Ph.D. François D. Beaulieu, B.Sc. Leslie-Ann Stewart, B.Sc. Jon Singer, B.Sc. Biomechanics, Laboratory, School of Human Kinetics, University of Ottawa, Ottawa, CANADA Motion Analysis Tools EMG Force platform Cine or Video camera Kinetic Analysis Causes of motion • Inverse Dynamics derives forces and moments from kinematics and body segment parameters • Support Moment shows effects of all moments of lower extremity • Joint Power Analysis determines contributions of each joint’s moment of force Divide Body into Segments and Make Free-Body Diagrams • Make freebody diagrams of each segment Apply Newton’s Laws of Motion to Terminal Segment • Start analysis with terminal segment(s), e.g., foot 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 Repeat with Next segment in Chain or Begin with Another Limb • Repeat until all segments have been considered, e.g., thigh Joint Power Analysis An Example from Sprinting • compute the angular velocity of the joint • compute the net moment of force at the joint 20. Extending 0. -20. Flexing SR11BJ 300. Extensor • multiply angular velocity and moment of force to obtain the “moment power” 0. -300. Flexor 2000. Concentric • this is the power produced by the net moment of force acting across the joint • it is mainly caused by muscle forces 0. -2000. Eccentric ITO CFS CTO -4000. 0.0 0.1 0.2 Time (s) IFS 0.3 0.4 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 Ankle angular velocity, moment of force and power 10 Dorsiflexion 0 -10 • Dorsiflexors produce dorsiflexion during swing 100 Trial: 2SFN3 Ang. velocity Moment Power Dorsiflexors 0 -100 • Plantar flexors control dorsiflexion Plantar flexion 100 Plantar flexors Concentric 0 • Large burst of power by plantar flexors for push-off -100 Eccentric -200CFS ITO 0.0 0.2 IFS CTO 0.4 0.6 Time (s) CFS ITO 0.8 1.0 1.2 Knee angular velocity, moment of force and power 10 Extension 0 -10 Flexion • Negative work by flexors to control extension prior to foot-strike • Burst of power to cushion landing • Negative work by extensors to control flexion at push-off 100 Trial: 2SFN3 Ang. velocity Moment Power Extensors 0 -100 100 Flexors Concentric 0 -100 Eccentric -200CFS ITO 0.0 0.2 IFS CTO 0.4 0.6 Time (s) CFS ITO 0.8 1.0 1.2 Hip angular velocity, moment of force and power 10 Flexion 0 -10 • Positive work by flexors to swing leg • Positive work by extensors to extend thigh • Negative work by flexors to control extension 100 Extension Trial: 2SFN3 Ang. velocity Moment Power Flexors 0 -100 Extensors Concentric 100 0 -100 Eccentric -200CFS ITO 0.0 0.2 IFS CTO 0.4 0.6 Time (s) CFS ITO 0.8 1.0 1.2 Support Moment • Used to quantify stability during stance of gait • Sum of ankle, knee and hip moments • Extensors moments are made positive Msupport = (-Mankle) + Mknee (-Mhip) • 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 (D.A. Winter, J Biomech, 13:923-927, 1980) Support Moment during Walking • Support moment is positive throughout stance • Typically has two peaks one after IFS and one before ITO 200. Support moment 100. Trial: CJWK 0. -100. Hip extensor 100. 0. -100. 100. Knee extensor 0. • Ankle plantar flexors are the most important from midstance to toe-off -100. 100. Ankle extensor 0. -100. IFS -200. 0.0 0.2 CTO CFS ITO 0.4 0.6 0.8 Time (seconds) 1.0 1.2 Stick Figure Animation Up One Stair Step from Landing Up One Step from Landing • Support moment similar to walking 200. Support moment Trial: STLUP7RH 100. 0. -100. • Larger than normal knee extensor moment in early stance 100. 0. -100. 100. Knee extensor 0. -100. 100. • Smaller ankle plantar flexor moment Hip extensor Ankle extensor 0. -100. IFS ITO -200. ITO 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3 Time (seconds) Similarities to Walking • Double support periods • Ground reaction forces have double peak • Cadence similar • Support moment is similar (always positive with two peaks) Differences with Walking • Peak forces slightly higher • Centre of pressure is concentrated under metatarsals, rarely near heel • Step height and tread vary from stairway to stairway • Railings may be present Stick Figure Animation A/K Amputee Walking Up One Stair Introduction • Investigate mechanics of descending stairs in forwards and backwards directions compared with level walking. • Why? Descending stairs is more difficult and dangerous than ascending stairs. • Falls from stair descent especially in the elderly can be fatal (Simoneau, et al., 1991; Winter, 1995) • Macleans: 236 Canadians died in 2000 from stair falls vs. 404 pedestrian deaths. Research Questions • How does stair descent differ from level walking? • Will peak moment and forces about the ankle, knee and hip be reduced in the backward stair descent versus forward descent? Laboratory Stairs • • • • Step height = 20 cm Step tread = 30 cm Railings = 91 cm Height and tread are adjustable Force platforms Study Design Forces & moments of force Ankle, Knee & Hip 10 healthy subjects (4 F + 6 M) •Warm up period •Descent Forward •Descent Backward •Descent Forward No previous at same speed as lower extremities backward injuries 5 trials each type of descent Support moment computed by adding 3 moments Msupport= -Mankle+ Mknee- Mhip (Winter, 1980) Work done by moments Leg closest to camera Moment powers Moment of force times joint angular velocity Stick Figure Animation Down Two Stairs to Landing Results • Stance phase was 65-70% of cycle (versus 60% for walking) • Differences in average cycle duration: forward (1.13 s) vs. backward (1.35 s) or 20% longer • Ground reaction forces were larger than walking • Forces were farther from stair edge with backwards Moments of Force (Support) Support moments larger with similar double peaks as walking 6 6 Support moment 3 3 0 0 -3 -3 Hip extensor 3 3 0 0 -3 -3 Knee extensor 3 3 0 0 -3 Ankle extensor 3 0 0 20 40 60 80 Percentage of Cycle Forwards Hip extensor Knee extensor -3 Ankle extensor 3 -3 0 Support moment 100 -3 0 20 40 60 Percentage of Cycle 80 Backwards 100 Show Animation Here Down Two Stairs Backwards to Landing Moments of Force (Ankle) Ankle plantar flexor reduced (means +/- 95th% CI) 6 6 Support moment 3 3 0 0 -3 -3 Hip extensor 3 3 0 0 -3 -3 Knee extensor 3 3 0 0 -3 Ankle extensor 3 0 0 20 40 60 80 Percentage of Cycle Forwards Hip extensor Knee extensor -3 Ankle extensor 3 -3 0 Support moment 100 -3 0 20 40 60 Percentage of Cycle 80 Backwards 100 Moments of Force (Knee) Knee extensor moment increased 6 6 Support moment 3 3 0 0 -3 -3 Hip extensor 3 3 0 0 -3 -3 Knee extensor 3 3 0 0 -3 Ankle extensor 3 0 0 20 40 60 80 Percentage of Cycle Forwards Hip extensor Knee extensor -3 Ankle extensor 3 -3 0 Support moment 100 -3 0 20 40 60 Percentage of Cycle 80 Backwards 100 Moments of Force (Hip) Hip moments small and highly variable with little power 6 6 Support moment 3 3 0 0 -3 -3 Hip extensor 3 3 0 0 -3 -3 Knee extensor 3 3 0 0 -3 Ankle extensor 3 0 0 20 40 60 Percentage of Cycle Forwards Hip extensor Knee extensor -3 Ankle extensor 3 -3 0 Support moment 80 100 -3 0 20 40 60 Percentage of Cycle 80 Backwards 100 Comparison with Walking Ankle Power: No initial dorsiflexor phase 5.0 Plantar Flexor 2.5 0.0 Plantar flexor eccentric phase was earlier and larger Plantar flexor concentric phase much smaller (just to clear step) Large variability during swing phase possibly due to uncertainty of landing -2.5 -5.0 Dorsiflexor 5.0 Concentric 2.5 0.0 -2.5 Eccentric -5.0 0 10 20 30 40 50 60 70 80 90 100 Percent cycle Forwards Comparison with Walking Knee Power: 5.0 Extensor 2.5 Little or no concentric extensor phase 0.0 -2.5 -5.0 Larger eccentric extensor phase at midstance Flexor 5.0 Concentric 2.5 0.0 Eccentric flexor power throughout swing same as walking -2.5 Eccentric -5.0 0 10 20 30 40 50 60 70 80 90 100 Percent cycle Forwards Ankle Moment and Power Larger peak eccentric power (5%) during weight acceptance Smaller peak plantar flexor push-off power 5.0 5.0 Plantar Flexor Plantar Flexor 2.5 2.5 0.0 0.0 -2.5 -2.5 -5.0 Dorsiflexor -5.0 Dorsiflexor 5.0 Concentric 5.0 Concentric 2.5 2.5 0.0 0.0 -2.5 -5.0 0 Eccentric 10 20 30 40 50 60 70 80 90 100 Percent cycle Forwards -2.5 -5.0 0 Eccentric 10 20 30 40 50 60 70 80 90 100 Percent cycle Backwards Knee Moment and Power Slightly more extensor concentric work Significantly reduced peak extensor eccentric power 5.0 5.0 Extensor Extensor 2.5 2.5 0.0 0.0 -2.5 -2.5 -5.0 Flexor -5.0 Flexor 5.0 Concentric 5.0 Concentric 2.5 2.5 0.0 0.0 -2.5 -5.0 0 Eccentric 10 20 30 40 50 60 70 80 90 100 Percent cycle Forwards -2.5 -5.0 0 Eccentric 10 20 30 40 50 60 70 80 90 100 Percent cycle Backwards Discussion Benefits of Backwards Stair Descent • 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 more inclined to use handrails • Moments and powers were smaller than forwards but larger than walking • No concentric ankle power needed (e.g., B-K amputees) Discussion Concerns with Backwards Stair Descent • Problems with seeing next step and landing • Unconventional therefore may affect compliance • Does require railings for most people • Irregular stairs may be problematic Stick Figure Animation A-K C-Leg Down Two Stairs to Landing A-K amputee Down Stairs Moment Powers: 4 Little or ankle power 2 Trial: C-Leg Hip 0 Large eccentric knee extensor phase at end of stance -2 -4 2 Knee 0 -2 Concentric hip flexor power at end of stance and into swing same as walking -4 2 0 -2 -4 0 Ankle 10 20 30 40 50 60 Percentage of Stride 70 80 90 100 Laboratory Ramp • • • • 10-degree incline one step before ramp opposite leg on ramp 2nd step on ramp Force platforms Stick Figure Animation Walking Up 10-degree Ramp Up a 10-Degree Ramp Moments: 3 Larger knee extensor moment at beginning of stance Ankle plantarflexor moment similar to walking Trial: RUAP03 1 0 Net moments of force (N.m/kg) Support moment similar to walking but smaller 2nd peak before ramp Support moment 2 Hip extensor -1 1 0 -1 Knee extensor 1 0 -1 Ankle extensor 1 0 -1 TO FS -2 0.0 0.2 0.4 0.6 0.8 FS 1.0 1.2 Time (seconds) TO 1.4 1.6 1.8 2.0 Up a 10-Degree Ramp Moment Powers: Larger concentric knee extensor phase at midstance Trial: RUAP03 250. H1 Hip powers H3 H1 H3 0. H2 H2 - 250. Knee powers 250. Power (watts) Concentric hip flexor power at end of stance and into swing same as walking 500. K2 0. K4 K3 - 250. K1 K3 500. A2 A2 Ankle powers 250. 0. Ankle power similar to walking A1 A1 - 250. FS - 500. 0.0 TO 0.2 0.4 0.6 0 .8 FS 1.0 1.2 Time (seconds) TO 1.4 1.6 1.8 2.0 Questions? Answers? Comments?