Transcript Kinetics versus kinematics for analyzing coordination

Descending Stairs:
Forwards and Backwards
François D.Beaulieu, MA
Lucie Pelland, PhD
D. Gordon E. Robertson, PhD
Biomechanics, Laboratory,
School of Human Kinetics,
University of Ottawa, Ottawa, CANADA
ISB –XIX New Zealand, 2003
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?
Methods
Use of 3 stair boxes with
30 cm tread
20 cm rise
Use of 3 Kistler force plates (last two steps + landing)
Use of 2 Panasonic Digital cameras
-left and right side
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
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
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
Chichen Itza – Il Castillo
Not the most dignified stair descent (5 point)
Thank you
Try it …
Its safer and
easier on the
knees and calf
muscles.
Questions?