Size and Proportions of Slow-Twitch and Fast-Twitch Muscle Fibers in Human Costal Diaphragm

Figure 2

Variability between subjects with regard to fiber diameters and fiber cross-sectional areas. CSA = cross-sectional area. Slow-twitch fibers (a, b) of costal diaphragm were smaller with regard to diameters and fiber cross-sectional areas than those of vastus lateralis muscle in all subjects. Fast-twitch fibers of costal diaphragm (c, d) were in 13/16 subjects smaller and in 3/16 subjects of similar size compared to those of vastus lateralis. Hybrid fibers (e, f) of costal diaphragm were in 12/16 subjects smaller, in 1/16 of similar size, and in 1/16 bigger than those of vastus lateralis. In 2/16 comparison was not possible, since hybrid fibers were absent in vastus lateralis muscle.

(a)

(b)

(c)

(d)

(e)

(f)