Transcript IFS - Faculty of Health Sciences | University of Ottawa

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
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
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
Motion Analysis Tools
EMG
Force platform
Cine
or
Video
camera
Electromyography
Noraxon system
Delsys
system
Bortec system
Mega
system
Kinematic Analysis
• Study of motion without
consideration of its
causes
• Motion description
• Based on Calculus
developed by Newton
and Leibnitz
Isaac Newton, 1642-1727
Kinematic Analysis
• Linear position
Manual goniometer
– Ruler, tape measure, optical
• Angular position
– Protractor, inclinometer,
goniometer
• Linear acceleration
– Accelerometry, videography
• Angular acceleration
– Videography
Miniature accelerometers
Motion Analysis
High-speed cinecamera
• Cinefilm, video or
infrared video
• Subject is filmed and
locations of joint
centres are digitized
Videocamera
Infrared
camera
Computerized Digitizing
(APAS)
Computerized Digitizing
(Simi)
Stick Figure Animation
Walking
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)
Force Platforms
2 Kistler force platforms
Ground reaction force
Steps for Inverse Dynamics
• Space diagram
of the lower
extremity
Divide Body into Segments and
Make Free-Body Diagrams
• Make freebody 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
Joint Power Analysis
• 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
Solid-Ankle, Cushioned Heel
(SACH) Prostheses
Stick Figure Animation
Walking with SACH foot
Ankle angular
velocity, moment
of force and
power of SACH
foot prosthesis
• Power dissipation
during weight
acceptance and
push-off
• No power
produced during
push-off
10.
Dorsiflexing
0.
-10.
Plantar flexing
100.
Dorsiflexor
Trial: WB24MH-S
Ang. velocity
Net moment
Power
0.
-100.
100.
Plantar flexor
Concentric
0.
-100.
Eccentric
-200.
ITO
0.0
IFS CTO
0.2
0.4
0.6
0.8
Time (s)
CFS ITO
1.0
1.2
1.4
FlexFoot Prostheses
(Energy Storing)
Recent models
Original model
Stick Figure Animation
Walking with FlexFoot prosthesis
Ankle angular
velocity, moment
of force and
power of FlexFoot
prosthesis
10.
Dorsiflexing
0.
-10.
Plantar flexing
100.
Dorsiflexor
Trial: WB13MH-F
Ang. velocity
Net moment
Power
0.
• Power returned
during push-off
-100.
250.
Plantar flexor
Concentric
0.
-250.
Eccentric
-500.
ITO
0.0
IFS CTO
0.2
0.4
0.6
Time (s)
CFS ITO
0.8
1.0
1.2
Ankle angular
velocity, moment
of force and
power of person
with hemiplegia
(stroke side)
15.
Dorsiflexing
0.
-15.
Plantar flexing
200.
Dorsiflexor
0.
• No power during
push-off
-200.
Plantar flexor
1000.
Trial: WPP14EG
Ang. vel.
Net moment
Power
Concentric
0.
-1000.
Eccentric
-2000.
IFS CTO
0.0
CFS
0.2
ITO
0.4
Time (s)
IFS
0.6
0.8
Ankle angular
velocity, moment
of force and
power of person
with hemiplegia
(normal side)
• Power at push-off
is reduced due to
slower gait
15.
Dorsiflexing
0.
-15.
Plantar flexing
200.
Dorsiflexor
0.
-200.
1000.
Plantar flexor
Concentric
Trial: WPN03EG
Ang. vel.
Net moment
Power
0.
• Negative power is
also reduced
-1000.
Eccentric
-2000. IFS CTO
0.0
0.2
CFS
0.4
Time (s)
ITO
IFS
0.6
0.8
Other Gait Patterns
Above-knee Prostheses
Stick Figure Animation
Walking with Terry Fox prosthesis
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
(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
• Ankle plantar
flexors are the most
important from
midstance to toe-off
200.
Support moment
100.
Trial: CJWK
0.
-100.
Hip extensor
100.
0.
-100.
100. Knee extensor
0.
-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
Laboratory Stairs
•
•
•
•
Step height = 24 cm
Step tread = 30 cm
Railings = 36 in.
Height and tread are
adjustable
Force platforms
Stick Figure Animation
Up One Step from Landing
Up One Step from Landing
• Larger than normal
knee extensor
moment
200.
Support moment
0.
-100.
100.
• Smaller ankle
plantar flexor
moment
Trial: STLUP7RH
100.
Hip extensor
0.
-100.
100. Knee extensor
0.
-100.
• Support moment
similar to walking
100.
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
• 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
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
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
Stick Figure Animation
Down Two Stairs to Landing
Down Two Stairs Forwards
• Larger than normal
negative power by
ankle plantar flexors
after foot-strike
(IFS)
500.
250.
Trial: CJRFD
Hip powers
0.
-250.
Knee powers
250.
0.
• Positive work done
after IFS by knee
flexors
-250.
500.
Ankle powers
250.
0.
-250.
ITO
-500.
0.7
0.9
IFS
1.1 1.3 1.5
Time (seconds)
ITO
1.7
1.9
2.1
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
Stick Figure Animation
Down Two Steps Backwards
Down Two Stairs Backwards
• Larger than normal
negative power by
ankle plantar flexors
after foot-strike
(IFS)
• No push-off power
needed from ankle
• No concentric knee
power required after
IFS
500.
Trial: CJLBD
Hip powers
250.
0.
-250.
Knee powers
250.
0.
-250.
500.
Ankle powers
250.
0.
-250.
-500.
ITO
IFS
ITO
0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1
Time (seconds)
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
Questions?
Answers?
Comments?