Biology Reference
In-Depth Information
5.1. Early manual methods for quantifying CSA
Early methods for measuring fiber size and CSA were reviewed in 1968 by
Aherne (1968)
. Such methods included projection of images of muscle tissue
on grid paper and counting the squares enclosed by each fiber outline
(
Sissons, 1965
), or alternatively, cutting out and weighing fragments of
the paper representing each fiber to calculate the cross-sectional areas
(
Bell and Conen, 1967
). Similar manual methods were still used by certain
investigators well
into the 1980s
(
Edman et al., 1988b; Glore and
Layman, 1987
).
The manual methods commonly utilized 40-50 years ago were
extremely time consuming and consequently, usually only a small number
of muscle fibers for each experimental group were analyzed. In addition,
certain measurements made using these early techniques were likely some-
what inaccurate. For example, CSAs of approximately 7000 and 4000
m
2
were reported for rat soleus and EDL muscles, respectively, derived using
projection methods (
Lieber et al., 1986
). Such high CSA values are repre-
sentative of human muscle, whereas rat muscle fibers are actually consider-
ably smaller (e.g., recent estimates of CSA for rat EDL were 2790 and
3137
m
m
2
for
Dow et al., 2004
and
Toth et al., 2008
, respectively).
m
5.1.1 Manual planimeters
In 1979-1984, polar planimeters were used to measure CSAs of muscle
fibers (
Maxwell et al., 1979, 1980; Staron et al., 1984
). Planimeters featured
a tracer arm containing a wheel and a counter with a scale, and were used by
moving the tracer point around the boundary of each muscle fiber. This
mechanical device significantly simplified the CSAmeasurements and allowed
measurements of dozens to hundreds of muscle fibers for each experimental
group. For example, human skeletal muscle in control subjects, weight lifters,
and distance runners were compared by analyzing CSAs of at least 25 fibers per
fiber type per muscle sample using a polar planimeter (
Staron et al., 1984
); for
Type IIA fibers of the vastus lateralis muscle, weight lifters featured muscle
fibers with higher CSAs than control subjects or runners. While useful, this
method was extremely time consuming and needed much improvement.
5.1.2 Interfacing of planimeters to computers
The planimetry was significantly improved with the emergence of personal
computers. The first systems for digitized planimetry were not very sophis-
ticated, but they significantly simplified and sped up muscle fiber CSA
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