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This involves muscle atrophy, reduction in number of muscle fibers and a shift towards "slow twitch" or type I skeletal muscle fibers over "fast twitch" or type II fibers. [3] The rate of muscle loss is dependent on exercise level, co-morbidities, nutrition and other factors.
Type I fibers are slow oxidative with a slow rise in force and an overall low force production. The type I fibers have a smaller fiber diameter and exhibit a slow contraction. Type IIa fibers are fast oxidative which exhibit fast contraction and a fast rise in force. These fibers have fast contraction times and maintain some, though not a great ...
“The proportion of slow-twitch to fast-twitch muscle fibers in a particular muscle varies depending on the function of the muscle and the type of training in which an individual participates.
Turtles, such as Trachemys scripta elegans, have complementary muscles within the neck that show a potential inverse trend of fiber type percentages (one muscle has high percentage of fast twitch, while the complementary muscle will have a higher percentage of slow twitch fibers). The complementary muscles of turtles had similar percentages of ...
In sarcopenic muscle the distribution of the types of muscle fibers changes with a decrease in type II muscle fibers, or "fast twitch," with little to no decrease in type I muscle fibers, or "slow-twitch" muscle fibers. Deinervated type II fibers are often converted to type I fibers by reinnervation by slow type I fiber motor nerves. [15]
The gastrocnemius muscle is heterogeneous, composed of both "red" and "pale" muscle, and thus containing fast-twitch high force fibers. Henneman's and colleagues took advantage of the differences between the soleus and gastrocnemius muscles to show that the neurons innervating the soleus muscle:
The properties used for distinguishing fast, intermediate, and slow muscle fibers can be different for invertebrate flight and jump muscle. [34] To further complicate this classification scheme, the mitochondrial content, and other morphological properties within a muscle fiber, can change in a tsetse fly with exercise and age.
The muscle fibers belonging to one motor unit can be spread throughout part, or most of the entire muscle, depending on the number of fibers and size of the muscle. [2] [3] When a motor neuron is activated, all of the muscle fibers innervated by the motor neuron are stimulated and contract. The activation of one motor neuron will result in a ...