Biomedical Engineering Reference
In-Depth Information
d
3
d
1
x
3
q
1
Lever
x
1
M
Muscle
FIGURE 13.20
Drawing of the classical isotonic experiment with inertial load and muscle attached to the lever.
The muscle is stretched to its optimal length according to experimental conditions and attached to the ground.
was that if mass was not reduced enough by the lever ratio (enough to be ignored), then
taking measurements at maximum velocity provided a measurement at a time when accel-
eration is zero, and, therefore, inertial force equals zero. If these two assumptions are valid,
then the experiment would provide data free of the effect of inertial force as the gravity
force is varied.
According to the experimental conditions, the muscle is stretched to its optimal length at
the start of the isotonic experiment. The isotonic experiment begins by attaching a load
,
stimulating the muscle, and recording position. The two curves in Figure 13.21 depict the
time course for the isotonic experiment for a small and large load. Notice that the durations
of both responses are approximately equal regardless of the load, in spite of the apparent
much longer time delay associated with the large load. Next, notice that the heavier the
load, the less the total shortening. Maximum velocity is calculated numerically from the
position data. To estimate muscle viscosity, this experiment is repeated with many loads
at the same stimulation level, and maximum velocity is calculated. Figure 13.22 illustrates
the typical relationship between load ratio (
M
P/P
o
) and maximum velocity, where
P
¼
Mg
0.01
0.008
Small Load
0.006
0.004
0.002
Large Load
0
−
0.002
−
0.004
0
0.04
0.08
0.12
0.16
0.2
Time (s)
FIGURE 13.21
The typical response of a muscle stimulated with a large and small load.
