Fig. 4. Sample recordings from the slack test measurements of
V0, the unloaded velocity of shortening from a red muscle
preparation. (A) Three superimposed recordings of tetanic force before and
after the length steps (
L) shown in B. The fibre bundle was
released by different distances from the same starting length. (C) Recordings
of force from A shown on expanded scales and with regression lines fitted to
the early part of the force redevelopment. The broken vertical lines marks the
time of the release. The horizontal arrow marks t, the time
from the release to the regression intercept for the largest step. This is the
time required to take up the slack following the length step. (D) Relationship
between step size, L, and t. The slope of the
regression line, 1.503±0.002 L0 s-1
(mean ± S.E.M., N=3), is V0 for this fibre
bundle. The intercept on the L axis,
0.053±0.0001L0 (mean ± S.E.M. N=3),
is an estimate of the compliance of the series elastic component (SEC) of this
fibre bundle. L0, the fibre length at which maximum
isometric force was produced, was 8.7 mm.
