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 .
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).