In contrast, the soleus muscle has oxidative fibers predominance and a
slow-twitch fibers majority (Table 1).
Endurance of the muscle is determined by
slow-twitch fibers and while power is determined by fast-twitch fibers.
However, the soleus is comprised primarily of
slow-twitch fibers (80 to 100%), which have lower hypertrophic potential in comparison to type II fibers (50).
The fast twitch fibers hydrolyze ATP faster than slow twitch and have greater reactivity in the presence of a basic pH, contrary to acidic pre-incubations in which
slow-twitch fibers present a more intensity of reaction (Kalmar et al., 2012; Latorre et al., 1993).
Although the mechanisms underlying such differences between fast- and
slow-twitch fibers are unclear, one potential explanation is that the different expression pattern of NOS isoforms between fiber types is associated with the different results of metabolic changes following L-NAME treatment.
PRT specifically works to strengthen both fast-twitch and
slow-twitch fibers in muscles, says Wilson.
In contrast, dancers who have more lean
slow-twitch fibers, which are responsible for endurance, can work for longer periods but often lack tone and require weight-lifting exercises to build muscle mass.
What's the difference between light meat and dark meat, or
slow-twitch fibers and fast-twitch fibers?
This finding was particularly interesting because it is exactly opposite of what would be expected from conventional fiber type-based explanations of EMG frequency, where fast-twitch fibers would have higher frequency EMG spectra than
slow-twitch fibers. It was hypothesized, however, that perhaps the strength-trained athletes had improved the ability to synchronize motor unit firings, which would increase the relative power in the low-frequency portion of the EMG spectrum [8].
Others that contract slowly are known as
slow-twitch fibers. Although a motor unit consists of only one kind of fiber type, most muscles have both fast- and
slow-twitch fibers.
Muscle fibers are categorized into "
slow-twitch fibers" and "fast-twitch fibers" (Squire, McConnell, & Zigmund, 2003).
Cross-sectional area of fast-twitch fibers was almost twice the size of
slow-twitch fibers (6,721 and 3,713 ^m2, respectively).