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).
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.
It's great that you are creating a better balance by focusing on the
slow-twitch fibers that increase your aerobic capacity.
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.
This would have resulted in an increase in the number of type I
slow-twitch fibers at the expense of type II fast-twitch fibers.
Others that contract slowly are known as
slow-twitch fibers.
Slow-twitch fibers (also called "Type 1 muscle fibers") activate and deactivate slowly, but when activated they are also very slow to fatigue.
Cross-sectional area of fast-twitch fibers was almost twice the size of
slow-twitch fibers (6,721 and 3,713 ^m2, respectively).
Although fast-twitch muscle fibers are usually larger in size than slow-twitch,
slow-twitch fibers can become up to 22% larger than fast-twitch fibers with effective endurance training.
