Biomedical Engineering Reference
In-Depth Information
reaction shear force is such as to cause the talus to move posteriorly under the
tibia. However, the line of pull of the major plantarflexors (soleus and gas-
trocnemius) is such as to pull the foot in an anterior direction. Thus, the total
shear force is drastically reduced from 800 N to about 300 N, and the muscle
action has been classified as an antishear mechanism.
5.4
PROBLEMS BASED ON KINETIC AND KINEMATIC DATA
1. (a)
Plot the vertical ground reaction force (Table A.5
a
in the Appendix
A) over the stance period (frames 28 - 69) and draw a line indicating
the body weight. Discuss the reasons why this force exceeds the body
weight during early stance and again during late stance. During the
period in midstance, when this force is less than the body weight, what
can we say about the acceleration of the center of mass of the body?
(b)
At heel contact right (HCR), the horizontal ground reaction force is
positive. What does this tell you about the way the heel made contact
with the ground?
(c)
If this subject were walking at a perfectly constant speed, how would
this be indicated in the horizontal ground reaction force curve? Was
this subject speeding up, slowing down, or at a constant speed?
2. (a)
Calculate the reaction forces at the ankle in the
x
and
y
directions
for frames 20 and 60, and compare your answers with those listed in
Table A.5
a
.
(b)
Calculate the ankle moment of force for frame 72 using appropriate
kinematic data plus data listed in Table A.5
a
. Discuss your answer in
terms of ankle function during early swing.
(c)
Repeat Problem 2
b
for frame 60. Discuss your answer in terms of the
role of the ankle muscles during late stance.
3. (a)
Given the calculated ankle reaction forces, calculate the reaction forces
at the knee in the
x
and
y
directions for frames 20 and 60 and compare
your answers with those listed in Table A.5
a
.
(b)
Given the calculated ankle reaction forces and moments of force,
calculate the knee moment of force for frame 90 using appropriate
kinematic data plus data listed in Table A.5
a
. Discuss your answer in
terms of the role of knee muscles during late swing.
(c)
Repeat Problem 3
b
for frame 35. Discuss your answer in terms of the
role of knee muscles during the weight acceptance phase of stance.
4. (a)
Given the calculated knee reaction forces, calculate the reaction forces
at the hip in the
x
and
y
directions for frames 20 and 60 and compare
your answers with those listed in Table A.5
b
.
(b)
Given the calculated knee reaction forces and moment of force, cal-
culate the hip moment of force from frame 90 using appropriate
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