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

Figure 3

Variability between subjects with regard to the numerical proportions of fiber types. Numerical proportion of slow-twitch fibers of costal diaphragm (a) was in all subjects around 50%, while in vastus lateralis muscle (b) this was the case only in 4/16 subjects and in the majority (11/16) slow-twitch fibers constitute about one-third of muscle fibers of vastus lateralis. In 1/16 subjects the proportion of slow-twitch fibers was around 70%. The proportion of hybrid fibers was small but varied considerably in both muscles; in costal diaphragm minimum was 0.1% and maximum 13.4% and in vastus lateralis minimum was 0.0% and maximum 14%.

(a)

(b)