Transcript Mechanics of pushing a loaded cart up an incline

Mechanics of Pushing a
Loaded Cart up an Incline
D. Gordon E. Robertson, Ph.D.
Dianne Ellwood, B.Sc.
Paul Johnson, B.Sc.
Dany Lafontaine, B.Sc.
School of Human Kinetics,
University of Ottawa, Ottawa, CANADA
Supported in part by Canada Post Corporation
Purpose
• to determine the functional role of the
three leg moments of force while
subjects push a heavily loaded cart up
a 10 deg incline
• to test whether resultant forces at
L5/S1 exceed 3400 N (NIOSH action
limit)
Methods
•
•
•
•
10 female subjects
cart loaded to 100 kg
five steps to 10 deg inclined ramp
force plates for last two footfalls before
ramp
• cinefilm at 50 fps, forces at 200 Hz
• inverse dynamics to obtain moments of
force at three leg joints for both legs
• computed work and power produced by
moments of force
Stick-figures of subject pushing loaded cart
up incline. Force vectors are shown under
two of the feet.
Results
• average velocity before ramp
was 1.75 m/s
• peak powers were similar in
magnitude to those of walking
but differed in pattern
Force signatures of last two steps
before ramp. Direction of motion is
left to right. Note, second force is
concentrated under ball of foot.
Ankle powers
• 8/10 subjects produced two or
more bursts of work by the
plantar flexors during second
last step before ramp
• 9/10 subjects produced two or
more bursts of work by the
plantar flexors during the last
step before ramp
Powers of the ankle, knee and hip moments
1000
Hip powers
500
0
-500
Knee powers
500
Trial: CP02CH
I Ankle
I Knee
I Hip
C Ankle
C Knee
C Hip
0
-500
Ankle powers
500
0
-500 IFS
0.0
CTO
0.1
0.2
CFS
0.3
0.4
ITO
0.5
0.6
Time (seconds)
0.7
IFS
CTO
0.8
0.9
1.0
Knee powers
• 5/10 subjects produced bursts
of positive work by the knee
extensors during second last
step
• 9/10 subjects produced bursts
of positive work by the knee
extensors during last step
Powers of the ankle, knee and hip moments
1000
Hip powers
500
0
Trial: CP06AU
I Ankle
I Knee
I Hip
C Ankle
C Knee
C Hip
-500
Knee powers
500
0
-500
Ankle powers
500
0
-500 IFS
0.0
CTO
0.1
0.2
0.3
0.4
CFS
0.5
ITO
0.6
0.7
Time (seconds)
IFS
0.8
0.9
CTO
1.0
Hip powers
• hip extensors performed
positive work during early part
of stance
• hip flexors performed negative
work during latter part of
stance
• 6/10 subjects performed as
described for second last step
• 8/10 subjects performed as
described for last step
Powers of the ankle, knee and hip moments
1000
Hip powers
500
0
-500
Knee powers
500
Trial: CP01TR
I Ankle
I Knee
I Hip
C Ankle
C Knee
C Hip
0
-500
Ankle powers
500
0
-500
IFS CTO
0.0
0.1
0.2
0.3
CFS
0.4
ITO
0.5
0.6
Time (seconds)
0.7
0.8
IFS CTO
0.9
1.0
Conclusions
• patterns of power production
differed from those of walking
• peak powers were similar in
magnitude to those of walking
• compressive forces at L5/S1 did
NOT exceed NIOSH action limit
(3400 N)
• standard lifting model is not
applicable to pushing